Delayed-type Hypersensitivity

Cell-mediated immunity (CMI) is a T-cell–mediated defense mechanism against microbes that survive within phagocytes or infect nonphagocytic cells. CMI functions to enhance antimicrobial actions of phagocytes to eliminate microbes. CMI manifests as delayed type cellular immune responses as typically seen in Mantaux test. This T-cell–mediated activation of phagocytes depends on interferon gamma (IFN-γ), a major cytokine produced by type 1 T-helper (Th1) cells. However, anti-IFN-γ neutralizing antibodies (Abs) do not completely abrogate CMI. IFN-γ or IFN-γR knock out (KO) mice do reveal attenuated CMI. These results indicate that CMI cannot be solely attributed to IFN-γ – mediated Th1 responses.

The identification of Th17 cells, which produce interleukins (ILs) – 17A, IL-17F, IL-21, IL-22, granulocyte-macrophage colony-stimulating factor (GM-CSF), and many other factors shed a light on the previously observed CMI in the absence of IFN-)γ. IL-17 KO mice did display attenuated delayed-type hypersensitivity (DTH) against bovine serum albumin and bacille Calmette-Guérin (BCG).[1] The role of Th17 and Th1 cells in CMI may vary depending on stimulants.[2]

Phagocytic cell activation and inflammation induced by CMI can cause tissue injury, typically called delayed-type hypersensitivity. In experimental animal models, delayed-type hypersensitivity responses are characterized by a granulomatous response consisting of macrophages, monocytes, and T lymphocytes. In skin, keratinocytes are also thought to have a role.

DTH responses in the skin have been used to assess CMI in vivo. An antigen (Ag) is introduced intradermally (ID), and induration and erythema at 48-72 hours postinjection indicate a positive reaction. Positive responses require the subject's exposure to the Ag at least 4-6 weeks prior to skin testing. The lack of a DTH response to a recall Ag is often regarded as an evidence of anergy. In the absence of underlying diseases, anergy may indicate primary or secondary T-cell immunodeficiency. The prototype recall Ag is Mycobacterium tuberculosis; other commonly used Ags for DTH responses in humans include tetanus, Candida and Trichophyton species, and mumps. Several fungi and streptococci Ags are no longer available or not recommended for clinical use.

DTH responses in the skin can also occur as contact hypersensitivity (CH) to certain chemicals, including nickel, dinitrochlorobenzene (DNCB), and picryl chloride. DTH reaction can also occur with various medications, including sulfonamides, phenytoin, and carbamazepine. These small chemicals are believed to act as haptens or activate T cells by directly binding to T cell Ag receptor (TCRs)/major histocompatibility complex (MHC).[3]

Originally, CH was thought to be skin DTH reaction. However, recent studies indicate that CH can be caused by different immune mechanisms. That is, in CH, CD4+ T cells are major effector cells, with CD8+ cell playing a regulatory role at least in certain model systems. In rodents, chemically induced CH was reported by attenuated by recombinant IFN-γ.[2]

CH induced by chemicals is enhanced by IL-17A, which induces production of IL-6, IL-8, GM-CSF, and upregulated expression of intercellular adhesion molecule (ICAM)-1 in human keratinocytes.[1, 2] In addtion, IL-4 KO mice revealed attenuated CH responses.[4] Cytotoxic CD8+ T cells that produce IL-17A (Tc17 cells) are also implicated in induction of CH in rodent models.[5] Thus, at least in rodent models, Th17 and Th2 cytokines have a role in induction of CH; Th17 cells produce IL-17A, and Th2 cells are a major source of IL-4.

A DTH reaction in the skin is initiated when certain Ags are presented by Ag-presenting cells (APCs) (ie, Langerhans cells to sensitized memory T cells). The Ag presentation and subsequent T-cell activation via CD3 and T-cell Ag receptor (TCR)(CD3/TCR) complex elicit an influx of macrophages, monocyte, and lymphocytes at the site of Ag exposure. These cells then produce inflammatory cytokines including tumor necrosis factor-α (TNF-α), IL-17A, and IFN-γ. At the onset of the DTH reaction, vasopermeability is increased by serotonin and histamine, and adhesion molecules are up-regulated in the vascular endothelium, so that additional cellular components migrate into the local site of Ag presentation.

The APCs present Ags complex in the groove of major histocompatibility complex (MHC) molecules expressed on the cell surface of the APCs. For most proten antigens or haptens associated with DTH skin reaction, CD4+ T cells are presented with Ags bound to MHC class II alleles, human leukocyte antigen (HLA)-DR, -DP, and –DQ. Specific MHC class II alleles are associated with excessive immune activation to certain Ags. For example, abacavir, an antiviral drug, causes severe adverse drug reactions exclusively in subjects with HLA variant B*57:01.[6, 7] Abacavir reactions are driven by drug-specific activation of cytotoxic CD8+ cells and this is implicated with abacavir's binding to the F pocket of the peptide-binding groove of HLA-B*57:01, resulting in alloreactive T-cell responses.[8]

T cells recognize Ags through TCRs, which are composed of heterodimers containing constant and variable regions (TCR α/ß and TCR γ/δ) analogous to the constant and variable regions of immunoglobulin. Most delayed-type hypersensitivity responses are elicited through TCR α/β T cells. TCR γ/δ is commonly expressed on T cells in the epithelium boundaries with limited TCR diversities. The function of TCR γ/δ T cells are not well understood in humans.

Ag elicited TCR activation is mediated by CD3 composed of γ, δ, and ε proteins and intracellular ζ chains. This CD3/TCR complex activation requires additional signaling mediated by CD4 or CD8 molecules which are physically associated with the CD3/TCR complex. In addition, Ag-mediated TCR activation requires Ag-independent signaling via co-stimulatory molecules which are not physically associated with the CD3/TCR complex. Co-stimulatory molecules that mediate activation signals such as CD28 and ICOS are constitutively expressed on T cells while inhibitory co-stimulatory molecules such as CTLA-4 (CD152) and PD-1 are up-regulated following T cell activation to abrogate excessive inflammatory responses.

DTH responses to some organisms are predominantly mediated by CD8+ cytotoxic T cells and effector stage Th1 cells augment CD8+ T cell activation. CD8+ T cells activate macrophages via CD40-CD40L interactions and production of Th1 cytokines including IFN-γ. The differences in T cell immune responses to intracellular microbes determine disease outcomes in certain diseases. For example, ineffective CMI is observed in patients with lepromatous leprosy with high Mycobacteria leprae load in macrophages and destructive skin lesions. While, in tuberculoid leprosy, strong CMI induces granulomas with less M Leprae load but severe sensory nerve defects.

IFN-γ is the key cytokine that plays the dominant role in DTH and is a major activator of macrophage-monocyte lineage cells; it augments phagocytic function and production of reactive oxygen intermediates (ROIs). IFN-γ also up-regulate T cell activation markers (CD69, CD71, CD25, and HLA-DR) and MHC molecules on APCs, promotes differentiation of Th1 cells while suppressing Th2 cell differentiation, and promote isotype switching of antibody (Ab) to facilitate Ab-mediated phagocytic cell immune responses. Recent studies also revealed a role of Th17 cells that produce IL-17A, IL-17F, IL-21, and IL-22.[1, 2, 9, 10] IL-17A was reported to amplify human contact hypersensitivity (CH) by rendering keratinocytes to susceptible to ICAM-1 dependent, Ag-non-specific T cell killing.[11]

IFN-γ also exerts regulatory actions on CD4+ Th cells.[12] IFN-γ affects activation-induced cell death of Th cells, contributing to lymphocyte homeostasis. IFN-γ is also reported to covert CD4+ CD25- Th cells into inducible CD4+ CD25+ regulatory T (Treg) cells by inducing Foxp3 expression. Lack of such IFN-γ actions is likely associated with excessive DTH reactions in patients with defects of IL-12–IFN-γ signaling pathways, which results in lack of IFN-γ actions.

TNF-α is also essential for DTH responses. Major cellular sources of TNF-α include macrophages and Th1 cells but this cytokine is also produced by many other lineage cells. TNF-α induces chemokine production from macrophages and endothelial cells and it also up-regulates expression of adhesion molecules on vascular endothelial cells, resulting in massive influx of inflammatory cells. In DTH responses to poison ivy and nickel, mast cells are likely a major source of TNF-α, in addition to production of other inflammatory mediators including histamine. TNF-α also induces inflammatory cytokines including IL-1. In rodent models of DTH, IL-1 but not IL-33 was found to be crucial for IFN-γ induced DTH reactions.[13]

Another key cytokine associated with DTH responses is IL-12. IL-12 is mainly produced by APC and Th1 cells. IL-12 augments production of IFN-γ and promotes Th1 cell differentiation. It also enhances cytolytic actions of NK and CD8+ T cells. IL-18 was also shown to augment IFN-γ production in the presence of IL-12. Osteopontin (OPN), a phosphoglycoprotein produced in the tissue, has also a role for promoting Th1 and Th17 driven DTH by supporting APC migration and IL-12 expression.[14, 15]

A defect in DTH reaction is best illustrated in the gene mutations of IFN-γ and IL-12 pathways. Gene mutation of IFN-γ receptor 1 (IFNGR1) is characterized by ineffective granuloma formation and disseminated infection of atypical Mycobacterium species, BCG, and Salmonella species.

The IFNGR1 gene consists of 7 exons (50 kb) and is highly polymorphic. Mutations identified thus far include frameshift deletions, insertion, a splice mutation, and missense mutations at the up-stream end of the gene. These mutations generally lead to absence of IFN-γ receptor protein expression or nonfunctional binding sites of IFN-γR for IFN-γ. This leads to impaired macrophage activation and resultant decreased production of TNF-α and ROIs. The gene mutations of IFNGR2 also cause similar clinical pictures. In contrast, mutations in IFNGR1 at a downstream hotspot disrupt the intracytoplasmic domain and result in a dominantly expressed disorder with milder clinical features.[16]

TH17 and Tc17 cells are also implicated with DTH and CH responses. For example, nickel-specific Th clones established from patients with nickel CH was shown to produce IL-17A.

Down-regulation of CMI in the immunocompetent host is an active process and important for minimizing tissue injury caused by DTH. Counter-regulatory cytokines such as IL-10 down-regulate production of Th1/Th17 cytokines or counteracts to Th1/Th17 cytokines. Naturally occurring and inducible regulatory T (Treg) cells also play a crucial role in this process, partly via production of IL-10 and TGF-ß.

Drugs that block components of DTH responses include antihistamines, histamine 2 (H2) receptor antagonists, and prostaglandin antagonists such as indomethacin. As indicated before, IFN-γ can augment induction of inducible Treg cells that produce IL-10 and TGF-ß in the late stage of DTH–induced inflammation to self-limit DTH reactions.[12] . It should be noted that effector Th cells can change lineage-specific functions depending on the microenvironment. That is, Th17 cells can acquire the ability of secreting Th1 cytokines and Th17 cells can also switch to Treg phenotype.[9, 10] Such flexibility is thought to be helpful for maintaining immune homeostasis and minimizing tissue damage associated with DTH responses in addition to effective microbial clearance.

Frequency

United States

More than 80% of healthy children aged 12-36 months mount positive DTH skin test reactivity to a Candida antigen. In the absence of a skin DTH response, evaluating CMI with in vitro lymphocyte proliferative responses to the specific Ag is necessary to confirm the anergic state.

Anergy is observed in patients with malnutrition, severe atopic dermatitis, and severe infections caused by M tuberculosis, measles, mumps, HIV, influenza, mononucleosis, lepromatous leprosy, and certain fungi. Anergy is also observed in patients who have recently received the measles, mumps, and rubella (MMR) vaccine, patients with sarcoidosis, or patients with parasitic infestations. In addition, immunosuppressive drugs, such as cytotoxic medications and corticosteroids, lead to anergy. Malignancy, especially malignant lymphomas, also induces anergy.

It should be noted that DTH reactions in patients with impaired IFN-γ and IL-12/IL-23 pathways tend to reveal excessive DTH reactions. In contrast, in patients with autosomal dominant or autosomal recessive hyper immunoglobulin E (IgE) syndrome with STAT3 mutations or DOCK 8 deficiency, decreased DTH responses against Candida may be observed due to deficiency of Th17 cells.[17, 18]

International

DTH reactivity to tuberculin is elicited by BCG vaccination. BCG is the most commonly administered vaccine throughout the world; however, it is not used in the United States.

Mortality/Morbidity

DTH skin testing is almost never associated with mortality or morbidity. The major error is associated with failure of differentiating anergy from negative DTH reactivity. Anergy may result from overwhelming infection such as sepsis or immunodeficiency. Secondary immunodeficiency is commonly due to therapy with corticosteroids, chemotherapy, calcineurin inhibitors (eg, cyclosporine, tacrolimus), and various monoclonal antibodies directed against the immune system.

Patients with T-cell immunodeficiency diseases such as severe combined immunodeficiency (SCID) are anergic.

Patients with mutations in IL12P40 or in IL12RB1 may show a positive, often excessive, DTH reactivity through activation of other components of DTH responses such as IL-17 and perhaps due to lack of regulatory effects of IFN-γ.

Mutations in IFNGR2, STAT-1, IL12P40, and IL12RB1 are autosomal recessive. Mutations found in complete IFN-γR deficiency are also autosomal recessive. Mutations in IFNGR1 that affect the downstream intracytoplasmic domain are autosomal dominant and are manifested as partial IFN-γR deficiency with less severe clinical manifestations. Patients with complete IFN-γR deficiency often succumb to death from overwhelming infection caused by nontuberculosis mycobacteria (NTM) and BCG at young age. Severe cytomegalovirus (CMV) infection is also described in these patients.

Mutations partially impairing IFN-γ signaling pathway may be manifested with milder mycobacterial infection, nontyphus Salmonella infection, Legionella infection, and listeriosis.

Race

Some individuals from the Mediterranean area have mutations leading to insufficient IFN-γ function. Specifically, a family from Tunisia, several families from Malta, and 1 family from Italy have been reported. Genetic defects involving the IFN-γ/IL-12 axis are now increasingly reported in other races.

Sex

Anergy to BCG and of idiopathic disseminated BCG infection are equally distributed among males and females. As expected in autosomal recessive gene mutations, IFNGR1, IL12P40, and IL12RB1 mutations are found with equal frequency in males and females.

Age

DTH reactivity to Candida Ag can be detected in infants as young as 3-4 months, but reactivity depends on exposure to the candida Ag. Positive DTH reactivity to tetanus toxoid requires completion of the primary immunization series of 3 injections administered 4-6 weeks apart; only one third of infants have a positive response to tetanus after the first dose of DTaP immunization. Patients with IFNGR1/IFNGR2 mutations that cause complete loss of IFN-receptor expression or IFN-γ–mediated signaling have presented as infants or in early childhood with disseminated BCG or NTM infections. This age-related infection seems to reflect the age of exposure to the causative organisms.

Delayed-type hypersensitivity (DTH) skin testing is usually performed to detect exposure to tuberculosis and, occasionally, when unusually extensive Candida infection has occurred. In these settings, the patient often has no prior history of unusually severe or opportunistic infections. In developing countries, ruling out confounding clinical malnutrition and rubeola infection that negate DTH skin test reactivity is crucial. HIV infection, sarcoidosis, and malignancies, such as Hodgkin lymphoma , also cause negate DTH responses.

Overwhelming infection such as sepsis is also known to cause suppresed DTH responses. One study indicated that this is mediated by CD8+ Treg cells through a TRAIL-dependent mechanisms and these cells are induced by apoptotic cells.[19]

The presence of any cause for immunosuppression modifies the interpretation of tuberculin DTH skin tests; in an immunosuppressive condition, 5-mm induration is interpreted as a positive response.

DTH skin reactions are absent in patients with lepromatous leprosy (M leprae), sarcoidosis, coccidioidomycosis, schistosomiasis, rheumatological diseases, severe viral infections (eg, influenza, mononucleosis, mumps), and those given the measles, mumps, rubella (MMR) vaccine recently (≤3 wk). Systemic steroid therapy can cause anergy; however, inhaled steroids with high bioavailability could also decrease DTH reactions and less frequently produce anergy when administered in large doses. Longer duration (>2 wk) and higher doses of oral steroids increase the risk for anergy, but no exact doses or duration predict induction of anergy in a given individual.

Other immunosuppressive agents that cause anergy include cancer chemotherapy agents, calcineurin inhibitors, and monoclonal antibodies against the immune system such as anti-TNF and anti-CD20 agents.

Usually, a patient with anergy caused by a T-cell immunodeficiency can be identified before wasting sets in. A pattern of unusually frequent or severe common infections, extensive mucocutaneous candidiasis, or dermatitis together with lymphopenia raises the suspicion of severe combined immunodeficiency (SCID) or other severe T-cell immunodeficiencies.

A patient with disseminated BCG or NTM infection may have a history of consanguinity or familial infection, indicating autosomal recessive genetic disorders. It is necessary to evaluate these patients for IFNGR1, IFNGR2, STAT-1, IL12P40, and IL12RB1 mutations. Patients with BCG infection usually present in early infancy after administration of the BCG vaccine. NTM infection develops more typically in mid childhood when community exposure to these mycobacteria occurs. A patient with one of the above mutations responds poorly to appropriate anti-mycobacterial therapy and often has a fulminant fatal infection.

Nontyphus Salmonella infections are more frequently observed in patients with the above-described disorders. Asthma, atopy, and immune complex disease (eg, glomerulonephritis, vasculitis, positive rheumatoid factors) are sometimes present.

Repetitive DTH skin testing does not change the parameters used to define a positive test result.

DTH antigens for coccidioidomycosis are no longer available. Diagnosis depends on identifying the organism or serology. Negative skin test reactivity to coccidioidin does correlate with a less favorable clinical outcome. However, the positive skin test result usually persists following an initial infection so that recurrence cannot be determined by the DTH skin testing.

DTH skin test reactivities for histoplasmosis and blastomycosis cross-react. In addition, positive DTH skin reactions in exposed but not infected individuals living in endemic areas confound interpretation. Both fungal infections have increased in incidence in HIV patients; these patients are frequently anergic. Diagnosis now requires culturing the organism, antigen/DNA detection, and/or serologic confirmation.

The DTH response in the skin is determined by the extent of induration. Erythema indicates an immediate hypersensitivity reaction and begins earlier than induration but often persists even after induration has developed.

DTH skn test to most antigens is read as positive when induration is 5 mm or more at 48 hours and 72 hours following inoculation. For tuberculin, 15 mm is considered a positive response for persons aged 4 years or older without risk factors; 10 mm is considered a positive response for younger children and those in populations with increased exposure or in whom immunosuppression is likely. A tuberculin reaction of 5 mm is considered positive when clinical evidence of tuberculosis, HIV infection, or close contact with people with infectious tuberculosis is noted.

Disseminated BCG and NTM infection are characterized by fever, wasting, lymphadenopathy, and hepatosplenomegaly.

A positive DTH response to the purified protein derivative (PPD) of M tuberculosis is elicited 4-6 weeks after exposure to M. tuberculosis. Populations at increased risk for tuberculosis include immigrants from countries with a high incidence of tuberculosis, such as African, Asian, and South American countries, and those with HIV infection. High-risk populations in the United States include those who are incarcerated, those who are homeless, migrant workers, and those who use illicit drugs. Individuals who are exposed to these populations are also at increased risk.

Anergy is discussed under History and Pathophysiology.

A single functional mature T cell can transfer DTH reactions; thus, a patient who received hematopoietic stem cell transplant from a donor with positive DTH responses to the specific antigen could reveal positive DTH responses to the same antigen.

Contact DTH reactions (contact hypersensitivity [CH]) occur in patients with poison ivy and nickel hypersensitivity

DTH to sulfonamides, phenytoin, and carbamazepine has been described. Reactions to penicillin-type antibiotics may be cell-mediated, but immunoglobulin G (IgG)-mediated responses are much more common.[20]

Genetic factors in CH are not well understood but studies targeting candidate genes revealed association of single nucleotide polymorphisms of some candidate genes in development of CH. These genes include NAT1, NAT2, GSTT, ACE, TNF, and IL-16.[21]

Characteristics of the Ags determine delayed-type hypersensitivity (DTH) skin test reactivity. Conjugation of the Ag to lipids facilitates DTH reaction. This explains the consistent response to mycobacteria in which Ag are isolated from the lipid cell wall. Size, valence, chemical composition, and dose are additional factors that are relevant to immunogenicity. Repetitive testing with the same Ag can cause an immediate IgE-mediated response and may diminish the DTH skin test reactivity. High doses of Ag that induce predominant Th2 responses, such as in miliary tuberculosis, abrogate the DTH responses by a negative feedback mechanism elicited by Th2 responses.

By convention, the Ags used for DTH skin testing are injected intradermally into the volar surface of the forearm with a volume of 0.1 mL each. Erythema and induration are measured at 24, 48, and 72 hours. A reaction at 24 hours does not represent DTH induced by CMI, or type IV reactivity. The Food and Drug Administration (FDA) –approved antigens for DTH skin testing are limited to PPD and Candida Ag.

Conventionally, children are tested with Candida and Dermatophytin in a 1:10 or 1:100 dilution and tested with tetanus in a 1:10 or 1:100 dilution of the diphtheria-tetanus (DT) vaccine. The higher dilution is used when the child has undergone a significant infection or unusually frequent immunization respectively.

Adults are initially tested with the 1:100 concentrations of these Ags.

When interpreting DTH skin reactivity, whether adequate exposure to the Ags has taken place prior to the procedure must be considered. A vigorous immune response to one Ag, such as in measles infection, leads to the abrogation of other DTH responses, for example, to PPD even though the patient is also infected with tuberculosis.

Ags that are poorly immunogenic in children and in some adults include mumps (no longer on the US market) and Trichophyton. Dinitrochlorobenzene (DNCB) and dinitrofluorobenzene (DNFB) have been superseded by in vitro assessments of CMI because of the risk of local tissue necrosis.

When an absent DTH reaction is noted, screening tests for a T-cell disorder should include enumeration of T and B cell subsets, and a chest radiograph to detect the thymus. Cell surface marker analysis of peripheral blood mononuclear cells (PBMCs) by flow cytometry and in vitro lymphocyte proliferation responses or production of T cell cytokins in response to mitogens (polyclonal stimulants) and recall antigens are also indicated.

Contact hypersensitivity to poison ivy and nickel is determined clinically; skin testing is not considered necessary. Nickel DTH reaction can be assessed by patch skin testing.

Adverse drug reactions to antibiotics, phenytoin, and carbamazepine may involve non-immune or immune-mediated mechanisms. The clinical setting of a reaction at 3 days or later with manifestation of a fixed rash with induration is more suspicious of involvement of a DTH response.

A chest radiograph to determine whether the thymus is present is an appropriate screening test for T-cell disorders only in the newborn period and early infancy; however, the thymus may involute in stressed infants in the context of overwhelming infection or severe congenital cardiac disease.

When DTH response is absent and a T-cell immunodeficiency is suspected, testing T-cell functions in vitro is indicated. Typically, lymphocyte proliferation responses against polyclonal stimulants such as mitogens (eg, phytohemagglutinins [PHA], concanavalin A [conA], pokeweed mitogen [PWM]) and specific antigens (eg, Candida, tetanus) are assessed. Measurement of production of IFN-γ, TNF-α, and IL-12 in response to various stimulants can also be helpful for screening severe T cell immunodeficiency as well as in mutations in IFNGR1, IFNGR2, STAT-1, IL12P40, or IL12RB1 when such mutations are suspected. Low levels of one or more of these cytokines increase the likelihood of these mutations.

In patients with severe eczema, recurrent skin abscesses, elevated IgE, and history of frequent bone fractures, assessment of IL-17 production or IL-17 expression in Th cells may be helpful. This is because patients with hyper-IgE syndrome caused by STAT3 mutation or DOCK8 deficiency have impaired development of Th17 cells, which is a major cellular source of IL-17.[17, 18]

Cell surface markers for monocytes, T-cells (CD4, CD8, CD28, TCR α/β, TCR γ/δ), and activated T cells (CD25, HLA-DR, and CD5) are reported to be normal in IFNGR1, IL12P40,STAT1,IL12RB1, STAT3 mutations. In profound primary T-cell deficiencies such as SCID, the pattern of cell surface marker expression of lymphocyte and natural killer (NK) cells may identify the type of T-cell defect in conjunction with the clinical manifestations.

Mutational analysis for IFNGR1, IFNGR2, STAT-1,STAT-3, IL12P40, and IL12RB1 is available in commercial laboratories and/or specific research laboratories.

Additional genes that control downstream immune responses initiated by IFN-γ in the DTH response are recognized; IFNGR2 does not bind IFN-γ but is needed for the activation of STAT-1 and its translocation to the nucleus.

See the list below:

• When disseminated BCG or NTM is suspected, perform biopsy of infected sites in order to examine granuloma formation and detect acid-fast mycobacteria.

• Tissue culture to detect mycobacteria is also indicated when disseminated BCG or NTM is suspected.

See the list below:

• Granuloma formation in an intact DTH response shows predominant infiltrates of activated macrophages and lymphocytes that can be identified as CD4+ T cells by immunohistochemical staining.

• When NTM infection is present, multinucleated giant cells formed by fused activated macrophages are observed in the immunocompetent host.

• In the patient with a T-cell defect, the formed granuloma lacks CD4+ T cells and these giant cells (due to ineffective macrophage activation by T cells). Instead, granulomatous lesions are characterized by infiltrate of polymorphonuclear cells, vacuolated cells, and macrophages.

• Mycobacteria may be present in abundance but are not frequently stained, although they are isolated by culture techniques.

Delayed-type hypersensitivity (DTH) skin testing requires the use of Ag doses as defined under Lab Studies. See Lab Studies for a more complete discussion of the interpretation of DTH reactions.

DTH responses represent cellular immune responses to recall Ags to which the subject has been exposed at least 4-6 weeks previously. The reaction occurs 48-72 hours after exposure and induces induration of 5 mm or more.

The inflammatory reaction may be sufficient to induce pain at the local site. Topical steroids and diphenhydramine have been used to decrease an unusually severe local reaction. If an excessive reaction is anticipated, such as in caseating tuberculosis, decrease the amount of Ag; for M tuberculosis, for example, decrease the strength of the PPD from the customary 5 units to 1 unit.

Negative reactions to a recall Ag to which the patient is known to have adequate exposure require investigation for an underlying illness or a T-cell immunodeficiency.

Positive DTH reactions do not indicate protection against the recall Ag that is tested. Antibody responses to the specific antigen usually reveal better correlation with immune protection.

In patients with mutations in the IFN)-γ/IL-12/IL-23 signaling pathways, medical care includes consideration of hematopoietic stem cell transplantation (HSCT) in patients with severe deficiencies and exogenous IFN-γ therapy in patients with partial deficiencies with milder clinical features. In the presence of NTM infection, patients require treatment with an aggressive regimen of anti-mycobacterial drugs. HSCT may not be successful in the presence of systemic, progressive NTM infection.

In a context in which a T-cell disorder is likely, a clinical immunologist should manage the diagnostic workup in order to obtain informative cell-mediated immunologic testing and appropriate mutational analysis.

Both types of evaluations for rare T-cell disorders are commonly available only in laboratories of specific investigators. However, intracellular cytokine staining of IL-17 and mutational analysis of genes associated with deficiencies of IFN-γ and IL-12 pathways can be attainable in the commercial laboratories.

Resolution of protein-energy malnutrition in immunocompetent hosts induces an intact DTH response.

PPD, which has been used to evaluate exposure to M tuberculosis, and Candida Ag are the only currently available US Food and Drug Administration (FDA)-approved Ags for delayed—type hypersensitivity (DTH) skin testing. The most clinically informative Ags used for DTH responses are Candida and tetanus Ags, because most individuals are exposed to these Ags as infants. By age 9-12 months, more than 80% of immunocompetent children mount positive responses to these Ags.

Previously available DTH Ags that were withdrawn from clinical use include the Cell-mediated immunity (CMI) multitest, coccidioidin, mumps, and histoplasmin. Mumps Ag is a relatively poor Ag in eliciting a positive DTH reactivity. Studies have shown only 60% of previously mumps infected adults to have a positive DTH reactivity. An even lower response is predicted when the only exposure to mumps is by MMR immunization.

Class Summary

These agents are used to detect infection with M tuberculosis.

Tuberculin, purified protein derivative (PPD Mantoux test, Aplisol, Tubersol)

The standard skin test uses 5 U of PPD in a volume of 0.1 mL. A lower concentration of 1 U/0.1 mL is used when a high exposure to antigen, as in caseating tuberculosis, is suspected; 250 U can be used if standard test result is negative and person is known to be immunocompromised. A negative DTH reaction does not rule out infection but may indicate disseminated infection as in miliary tuberculosis.

Class Summary

These are used to assess cell mediated immunity (CMI) following the primary series of diphtheria-tetanus-a cellular pertussis (DTaP) vaccine (3 doses). Conventionally, it has also been used as a control for tuberculin testing in patients who are immunocompromised or suspected to have disseminated tuberculosis.

Tetanus toxoid adsorbed or fluid

The standard TD vaccine is diluted to 1:100 or 1:10. A positive DTH reaction indicates recognition by cell-mediated immunity; protection correlates with antibody responses.

Class Summary

Most infants have been exposed to Candida antigen (Ag) even without clinical thrush or Candida diaper dermatitis. Japanese studies showed that 80% of children had positive DTH responses by age 1 year; therefore, Candida is a conventional Ag used as a positive control for tuberculin skin testing in individuals who are immunocompromised or when disseminated tuberculosis is suspected.

Candida skin test antigen (Candin, NDC#38697-200-1; Allermed)

Also known as Dermatophytin. It is diluted 1:10 or 1:100 with sterile water.

Consider patients with most T-cell disorders for stem cell transplantation, usually by bone marrow transplantation using a HLA-matched related or unrelated donor.

Only a few cases of bone marrow transplantation (BMT) have been reported in patients with mutations in the interferon (IFN)-γ and interleukin (IL)-12/IL-23 signaling pathways with rather unfavorable results. Intact T-cell functions other than IFN-γ/IL-12/IL-23 axis increases the risk of graft rejection and concurrent NTM infection usually present at the time of BMT increase the risk of post-BMT complications.[22, 23]

Patients in whom immunodeficiency causing impaired CMI is suspected should never receive the BCG or smallpox vaccine. Similarly, live vaccines (MMR and varicella) are contraindicated, although this vaccine is not administered until age 1 year, by which time most T-cell disorders have been diagnosed. Guidelines regarding the administration of the MMR vaccine have been updated.[24]

Patients with IFNGR1, IFNGR2, STAT-1, IL12P40, or IL12RB1 mutations are advised to receive prophylaxis against NTM using rifabutin and clarithromycin.

Antigens that are currently available for DTH skin testing are not associated with significant morbidity and do not cause mortality.

Experimental animal models of immunodeficiency with absent DTH reactivity suggest that other infections may also occur in the absence of effective CMI. These infections include L monocytogenes, L pneumophila, T gondii, and Leishmania species.

In humans with idiopathic disseminated BCG or with mutations in the IFN-γ signaling pathway, the risk of contracting nontyphus Salmonella infections increases.

One report describes severe infections with viruses (eg, respiratory syncytial virus [RSV], parainfluenza virus, herpes simplex virus (HSV), cytomegalovirus [CMV], and varicella-zoster virus [VZV]) in a patient with an IFN-γ signaling pathway defect.

Some patients with IFNGR1 mutations have good antibody responses to HSV, CMV, VZV, and Epstein-Barr virus (EBV) without clinical infection, suggesting that their host response to these viruses is intact.

Adequate nourishment and discontinuation of drug therapy can reverse anergy caused by malnutrition and immunosuppression by immunomodulating agents, respectively.

As noted in Mortality/Morbidity, severe mutations in IFNGR1, IFNGR2, STAT-1,IL12P40, and IL12RB1 lead to lethal disseminated infections with NTM. Mutations in the IFN-γ signaling pathway that cause milder clinical infections are described; many of these patients benefit from exogenous IFN-γ therapy.

 

Regarding IFNGR1, IFNGR2, STAT-1, IL12P40, and IL12RB1 mutations, inform families about the risks of infection so that appropriate steps to avoid exposure to infection are instituted.

• Families should be aware that BCG and live viral vaccines are contraindicated.

• Genetic counseling is an essential as a part of medical care for the family. Inform parents of the 1 out of 4 risk for affected infants in autosomal recessive gene mutations. Mutations in the intracytoplasmic domain of IFNGR1 result in autosomal dominant transmission.

• If hematopoietic stem cell transplant (HSCT) is considered as a therapeutic option, an adequate informed consent from for HSCT must include the high risk for life-threatening infection during the preparative immunosuppressive regimen in addition to the risk for failure to engraft and graft versus host disease (GVHD). Although successful complete immune reconstitution from HSCT can be obtained using fully HLA matched related and unrelated donors, patients may not engraft or may experience GVHD post-transplant. Other forms of stem cell reconstitution that can be offered include cord blood cell transplantation. Gene therapy is expected to be an option in the future.

The Immune Deficiency Foundation is an important resource for education and for support for patients and families with any primary immunodeficiency disease. The current address is 40 W. Chesapeake Ave, Suite 308, Towson, MD 21204. Some states have local chapters.

The Jeffrey Modell Foundation at 747 Third Avenue, New York, NY 10017 provides support and raises funds.

For excellent patient education resources, visit eMedicineHealth's Allergies Center.