Leukocyte Adhesion Deficiency

Leukocyte adhesion deficiency (LAD) is a rare primary immunodeficiency.[1, 2] The clinical picture is characterized by marked leukocytosis and localized bacterial infections that are difficult to detect until they have progressed to an extensive level secondary to lack of leukocyte recruitment at the site of infection. Thus the infections in patients with leukocyte adhesion deficiency act similarly as those observed in patients with neutropenia. See the images below.

Labial ulceration from which Escherichia coli was cultured in an 8-month-old girl with leukocyte adhesion deficiency type 1 (LAD I). Note the thin bluish scar at the superior aspect of the labia from an earlier cellulitis.

This 3-year-old girl had leukocyte adhesion deficiency type I (LAD I) with complete absence of CD18 expression. Note the typical gingivostomatitis, which was culture-negative for any pathogen.

This 10-month-old patient with severe leukocyte adhesion deficiency type I (LAD I) developed a cervical adenitis caused by Klebsiella pneumoniae. Following incision and drainage, wound healing took 4 months.

Leukocyte adhesion deficiency type I (LAD I) is a failure to express CD18, which composes the common ß2 subunit of LFA1 family (ß2 integrins). CD11a/CD18 (LFA-1) expressed on lymphocytes is known to play an important role in lymphocyte trafficking (adhesion to vascular endothelium), as well as interactions to antigen presenting cells (APC). LFA-1 also plays a role of cytotoxic killing by T cells. Another member of this family is CD11bCD18 (MacA or CR3) and CD11cCD18(CR4). These 2 members mediate leukocyte adhesions to endothelial cells but they also serve as receptors for iC3b (inactivated C3b). These patients succumb to life-threatening infection, usually within 2 years of life in severe cases of leukocyte adhesion deficiency I (< 1% expression of CD18). In milder forms of leukocyte adhesion deficiency I (1-30% expression of CD8), patients may survive to adulthood.

Leukocyte adhesion deficiency type II is extremely rare; only a handful cases have been reported and most of them are of Middle Eastern decent. It is a defect in the expression of ligands for selectins due to lack of enzymes required for expression of selectin ligands. Patients have leukocytosis, recurrent infections (more prominent in infants and toddlers), and severe growth and mental retardation. This disease is a defect in fucose metabolism (lack of fucosylation of the carbohydrate selectin ligands) that results in failure to express the ligand for E and P selectin, sialyl Lewis-X (CD15s) expressed on leukocytes and endothelial cells. The patients are unable to fucosylate other glycoproteins, including the H blood group polysaccharide.

Patients with leukocyte adhesion deficiency II manifest the Bombay phenotype (ie, negative for O and H blood group antigens with potential production of anti-H antibody). The immunoglobulin M (IgM) and immunoglobulin G (IgG) heavy chains are also not fucosylated. However, IgM and IgG serum levels are within the reference range in patients with leukocyte adhesion deficiency II.

Leukocyte adhesion deficiency II may be classified as one of the congenital disorders of glycosylation (CDG), a rapidly expanding group of metabolic syndromes with a wide symptomatology and severity. All stem from dysfunctional N -glycosylation of proteins. Currently, 18 subtypes have been reported: 12 are type I (dysfunctional lipid-linked oligosaccharide precursor synthesis), and 6 are type II (dysfunctional trimming/processing of the protein-bound oligosaccharide), including leukocyte adhesion deficiency II (CDG-IIc).[3]

Variants of leukocyte adhesion deficiency have also been reported, including fully expressed but nonfunctional CD18 and an E selectin that is expressed but rapidly cleaved from the cell surface (only present in soluble form). Another reported type of leukocyte adhesion deficiency involves dysfunction in platelet aggregation in addition to a defect in leukocyte adhesion. Thus, patients with this type of leukocyte adhesion deficiency manifest both severe bacterial infections and bleeding disorder. This leukocyte adhesion deficiency variant is associated with defective expression of the Rap-1 activator CalDAG-GEFI. Rap-1 is an essential protein involved in signaling mediated by integrins.

More than one leukocyte adhesion deficiency variant has been labeled leukocyte adhesion deficiency type III (LAD III), creating confusion in the literature.

Peripheral blood leukocytes undergo a sequence of activation that leads to migration of cells into the site of inflammation. First, the cells roll along endothelial surfaces, a process that requires expression of P and E selectins on the endothelial cells and their ligands on leukocytes. Rolling is a reversible process, partly because E selectin is shed from the cell surface and P selectin is internalized in endothelial cells. Next, cells adhere to the endothelial surface and enter the tissues by diapedesis; this process requires the family of integrins. Most importantly, CD18 is the essential component of the ß2 integrins CD11a/CD18, CD11b/CD18, and CD11b/CD18. Ligands of ß2 integrins expressed on endothelial cells belong to the Ig supergene family.

ß2 integrins are heterodimeric glycoproteins that are expressed as transmembrane proteins that transmit signals from the extracellular surface to cytoskeletal proteins. As such, CD18 is an integral part of other phagocytic functions. CD11b/CD18 (Mac-1) on myeloid cells is a receptor for iC3b and, thus, is important for recognizing bacteria and other microorganisms opsonized with iC3b. This recognition leads to phagocytosis and efficient microbicidal activity by the neutrophil, monocyte, or macrophage. Lymphocyte function antigen-1 (LFA-1) or CD11a/CD18, promotes adhesion by its expression on lymphocytes, monocytes, and neutrophils but also plays a role as one of the costimulatory molecules between lymphocyte and APC interactions. The third β2 integrin is CD11c/CD18 (p150/95) and is expressed on myeloid cells and some natural killer cells.

Binding of CD11/CD18 to ligands induces intracellular signaling that activates multiple cellular functions including cytokine production, cytotoxicity, apoptosis, and proliferation.

The major selectin ligand, sialylated Lewis X (SleX), is absent in leukocyte adhesion deficiency II. SleX, or CD15s, is a blood group tetrasaccharide. Both the sialic acid and the fucose moieties of SleX are needed for binding to the selectins; a primary defect in fucosylation in leukocyte adhesion deficiency II results in absence of fucosylated glycans in the cell surface including SleX.

Two other integrins are known to induce adhesion to extracellular proteins such as fibronectin, collagen, and laminin. These are members of the ß1 integrin subfamily, α4ß1, and the α4ß7. Both are expressed on lymphocytes, eosinophils, and natural killer cells.

Irish setter dogs and Holstein cattle have a disorder similar to human leukocyte adhesion deficiency I with leukocytosis and increased infections. This is secondary to a mutation in the gene homologous to human CD18. Both strains serve as promising large-animal models for leukocyte adhesion deficiency.

Knockout mice have been developed with the genes deleted for many of the adhesion-related molecules, (eg, CD18, CD11a, CD11b, ICAM1, ICAM2; E, P, and L selectins; fucosyl transferase; acetylglucosaminyltransferase). The murine models have milder disease than LAD I in humans, and no growth or mental defects as observed in murine leukocyte adhesion deficiency II models; most knockout mice strains revealed mild-to-moderate neutrophilia, but infections are absent except for CD18 knockout mice.

Frequency

United States

Leukocyte adhesion deficiency I has been reported in fewer than 400 individuals; 75% have the severe form, expressing less than 1% CD18. Only a handful of children have been described with leukocyte adhesion deficiency II. Three cases of with variant leukocyte adhesion deficiency I or decreased cell-expressed E selectin have been reported in the literature.

International

Although leukocyte adhesion deficiency I is rare, it is reported worldwide, indicating a lack of ethnic predisposition. Patients with leukocyte adhesion deficiency II are mainly reported in the Middle East and Brazil.

Mortality/Morbidity

Most patients with severe leukocyte adhesion deficiency I succumb to death within the first year of life. Bacterial infections not treated with stem cell transplantation are responsible for most deaths. Life-threatening viral infections are less frequently reported; however, aseptic meningitis and croup-like syndromes are well known complications as described in a 1985 review by Anderson et al.[4]

Patients with leukocyte adhesion deficiency II usually do not succumb to death with infections but develop severe mental retardation and developmental delay, neurologic impairment, and short stature. Periodontitis and colitis in rare occasions may be found in older individuals with leukocyte adhesion deficiency II.

Race

Leukocyte adhesion deficiency I can affect people of all racial groups. Leukocyte adhesion deficiency II has been reported only in people from the Middle East and Brazil.

Sex

Approximately equal numbers of males and females are affected, which is consistent with the autosomal recessive inheritance in both leukocyte adhesion deficiency I and leukocyte adhesion deficiency II.

Age

Most patients present within the first several months of life. Delayed umbilical cord separation beyond the normal range of 3-45 days is the classic presentation for leukocyte adhesion deficiency I. Patients who are less severely affected may not be identified until periodontitis develops with tooth eruption; oral ulcerations may be present at the same age. Patients who survive into childhood without hematopoietic stem cell transplantation (HSCT) express some CD18 on leukocytes and have less severe infections.

Patients with leukocyte adhesion deficiency II do not have delayed umbilical cord separation. They may be identified by their characteristic facial appearance and growth failure and, in some cases, by prenatal ultrasonography.

See the list below:

• Leukocyte adhesion deficiency type I (LAD I) may be diagnosed prior to the onset of infections when delayed umbilical cord separation (normal separation is 3-45 d, with a mean of 10 d) is observed with a persistently high WBC count (>20 X 109/L) in the absence of infection. Patients with leukocyte adhesion deficiency I typically experience from omphalitis, perirectal and labial cellulitis, infections classically seen in patients with neutropenia, otitis media with minimal inflammation, and other indolent necrotic skin infections. Pus is not present, but serosanguineous fluids may be present.

• The most common infectious agents that affect patients with leukocyte adhesion deficiency I include Staphylococcus species, enteric gram-negative bacteria, and fungal organisms, usually Candida albicans. With tooth eruption, gingivitis and periodontitis develop. Wound healing is delayed with poorly formed, thin, and bluish scars. Less frequent, but well-described, complications include aseptic meningitis and croup syndromes of poorly defined etiology. Bacterial typhlitis (inflammation of the cecum commonly found in patients with neutropenia) and intestinal perforation are difficult to diagnose in a timely fashion in patients with leukocyte adhesion deficiency I. Infection is the major cause of death in patients with leukocyte adhesion deficiency I.

• Delayed umbilical cord separation is the classic presentation of leukocyte adhesion deficiency I. However, it is not a reliable finding. In patients with leukocyte adhesion deficiency I, delayed umbilical cord separation is associated with neutrophilia, whereas healthy infants with delayed cord separation lack an elevated WBC count. Omphalitis and perirectal or labial cellulitis associated with extreme neutrophilia (WBC count approximately 45 X 109/L) is highly suggestive of leukocyte adhesion deficiency I.

• Microbicidal activity and oxidative responses against bacteria and Candida species have been shown to be impaired in leukocyte adhesion deficiency I.

• To date, patients described with leukocyte adhesion deficiency II have been of Middle Eastern and Brazilian descent with poor intrauterine or postnatal growth and severe mental retardation recognized shortly after birth. Consanguinity should be sought. Infections in leukocyte adhesion deficiency II are rarely life threatening, but the typical skin and mucosal infections of leukocyte adhesion deficiency I with equally dramatic leukocytosis and absent pus may be observed. Older patients usually manifest fewer infections.

See the list below:

• For patients with leukocyte adhesion deficiency I, fever is the initial manifestation of infection. Skin and mucosal sites of infection must be rigorously inspected because the inflammatory response is so indolent. Cellulitis, necrosis, and serosanguineous fluid characterize local infection in leukocyte adhesion deficiency I.

• Patients with leukocyte adhesion deficiency II have a characteristic facial appearance, short stature, limb malformations, and severe developmental delay.

See the list below:

• Leukocyte adhesion deficiency I is an autosomal recessive disorder caused by mutations in the gene that codes for CD18, the ß chain of ß2 integrins, mapped to chromosome arm 21q22.3. In 50% of patients with leukocyte adhesion deficiency I, the gene defects are point mutations of CD18; missense, nonsense, and splice mutations comprise the remainder. Usually, the alleles have 2 distinct mutations. LAD I variants with CD18 that is nonfunctional because of abnormal conformational changes have also been described.

• Leukocyte adhesion deficiency II is caused by mutations in a gene that codes for guanosine 5'-diphosphate (GDP) fucose transporter, which transports GDP fucose to the Golgi complex where glycan, including sialyl Lewis X (the ligand for E and P selectins), are fucosylated. These mutations cause a defect in fucose transport that also results in the nonimmunologic features of severe growth and mental retardation. Thus far, most patients have presented in consanguineous families, consistent with double homozygosity of the alleles.

• Helmus et al identified a genetic defect of leukocyte adhesion deficiency II in a patient whose Golgi GDP-fucose transporter (GFTP) bore a single amino acid exchange that rendered this protein nonfunctional but correctly localized to the Golgi.[5] They also reported a novel dual defect in which a truncated GFTP is unable to localize to the Golgi complex, causing leukocyte adhesion deficiency II in one patient. Furthermore, the missing part of the GFTP can be dissected into 2 regions: one that is needed for Golgi localization, and one that is required for the function of the GFTP. All patients with leukocyte adhesion deficiency II who are genetically analyzed may be subdivided into 2 groups: one in which single amino acid exchanges in the GFTP impair its function but not its subcellular localization, and another group with a dual defect in function and Golgi expression of the GFTP due to the absence of 2 important molecular regions.

• A leukocyte adhesion deficiency II variant with an absence of cell-associated E selectin but with the presence of the soluble E selectin has also been reported.

• Other variants have been reported, creating the potential for confusion and highlighting the need for a common classification. Alon et al have reported a new form of leukocyte adhesion deficiency associated with defective expression of the Rap-1 activator CalDAG-GEF (guanine exchange factor), resulting in impaired signaling via G-protein–coupled receptor (GPCR) at endothelial contacts.[6] Kinashi et al report an inherited activation defect in Rap1, a small guanosine triphosphate (GTP)ase that works as a key regulator of inside-out integrin activation, associated with a pathologic disorder in leukocyte integrin function.[7] Both groups have labeled their finding, leukocyte adhesion deficiency III. These defects also impair platelet aggregation, leading to bleeding disorders. McDowall et al studied the effect of two mutations in the kindlin3 gene on leukocyte function in vitro.[8]

• Impaired leukocyte adhesion can be caused by 2 common drugs (ie, epinephrine and corticosteroids). Both of these drugs demarginate neutrophils from the peripheral vasculature. The mechanism for steroid demargination is not well understood. Epinephrine acts by causing endothelial cells to release cyclic adenosine monophosphate, which, in turn, interrupts adherence.

• A dominant-negative mutation in Rac2 is reported to cause a clinical syndrome indistinguishable from leukocyte adhesion deficiency I. Integrin expression is intact, but actin-associated functions, such as shape change and chemotaxis, and generation of superoxide dependent on nicotinamide adenine dinucleotide phosphate (NADPH) oxidase are defective. Rac2 is a cytosolic GTP–binding protein that acts in a signaling pathway of chemokine receptor-mediated activation of cellular events essential to microbicidal activity.

See the list below:

• In leukocyte adhesion deficiency (LAD), the CBC count typically reveals leukocytosis (WBC count >20 X 109/L) in the absence of infection; leukocytosis dramatically increases with infection (WBC counts of 40-100 X 109/L are common).

• Flow cytometry is used to assess the presence of the β2 integrins CD11a/CD18 (LFA-1 or aL/b2) on leukocytes, CD11b/CD18 (Mac-1 or aM/b2) on myeloid cells, and CD11c/CD18 (p150,95 or aX/b2) on myeloid cells.

• In leukocyte adhesion deficiency II, the Bombay blood group phenotype is detected.

• Preimplantation genetic diagnosis (PGD) of leukocyte adhesion deficiency I offers promise. The application of preimplantation genetic diagnosis has been developed to achieve a healthy pregnancy in one child.[9] Thus, some evidence suggests that, for couples carrying mutated genes, traditional prenatal diagnosis and the decision of whether to terminate a pregnancy might not be acceptable because the application of PGD provides an alternative.

See the list below:

• CT scanning and MRI are essential for diagnosis of abdominal infections in these patients because of the defective phagocytic mobilization to the site of infection. Plain radiographic findings are often misleading because of the absence of pus or lobar consolidation in pneumonia.

• Bone scanning and gallium scanning may be useful modalities in localizing infection in selected patients. Because gallium relies on the presence of phagocytic cells, gallium scan findings are most likely to be informative when patients with leukocyte adhesion deficiency have residual expression of integrins or when granulocytes are transfused to patients with severe leukocyte adhesion deficiency (absence of CD18 expression).

See the list below:

• In leukocyte adhesion deficiency I, assays of random migration, chemotaxis, phagocytosis, and killing by neutrophils invariably show deficits in these functions. Phagocytic and killing defects are caused by the impaired recognition of iC3b-opsonized organisms. Antibody-mediated cellular cytotoxicity is also impaired.

• In leukocyte adhesion deficiency I, lymphocyte functions requiring LFA-1 (the CD2 pathway) are impaired; mitogen responses may be decreased. The relationship of in vitro lymphocyte defects to clinical infections is not understood. Although antibody responses to the T-dependent phiX174 bacteriophage were found to be impaired, immunoglobulin levels and specific antibody responses to vaccines are typically normal.

• Leukocyte adhesion deficiency II is not associated with defects in lymphocyte or antibody function. The decrease in biochemical activity of guanosine 5'-diphosphate-D-mannose dehydratase (GMD) may be measured.

See the list below:

• Bronchoscopy may be required to identify the etiology of pulmonary infection.

• Spinal taps have been carried out without complication.

• Surgical procedures are fraught with difficulty caused by the extremely delayed healing. In the author's experience, wet-to-dry dressing changes are successful in promoting healing; granulocyte transfusions were not clinically successful.

See the list below:

• In both leukocyte adhesion deficiency I and leukocyte adhesion deficiency II, localized infections lack neutrophilic infiltrates or pus formation; edema and necrosis are the prominent findings.

See the list below:

• Bone marrow and other stem cell transplantation are the therapies of choice in leukocyte adhesion deficiency (LAD) and have a very high success rate.[10, 11, 12] Thus, bone marrow or other stem cell reconstitution is a first-line treatment for severe leukocyte adhesion deficiency type I, in which less than 1% CD18 expression is detected. Donors may provide human leukocyte antigen (HLA)-matched, related, haploidentical, or unrelated HLA–matched hematopoietic stem cells. The high rate of successful engraftment in patients with leukocyte adhesion deficiency I is thought to be due to absence of CD11a/CD18 expression on lymphocytes; antibodies directed against this integrin also seem to improve engraftment of bone marrow stem cells and prevent graft versus host disease in patients who underwent hematopoietic stem cell transplantation (HSCT) for other disorders. However, not all patients are candidates for early bone marrow transplants.

• Other intervention measures for leukocyte adhesion deficiency I have included prophylactic antibiosis, interferon-gamma, and leukocyte transfusions; none of these has shown significant benefit.

• Gene therapy with insertion of the CD18 subunit is currently under investigation. Because patients with decreased expression of CD18 (1-30%) have a milder disease, partial reconstitution is anticipated to provide clinical benefit.

• Leukocyte adhesion deficiency II does not require prophylactic antibiosis. Fucose replacement administered orally or intravenously has variable effectiveness in improving phagocytic functions.

• The use of granulocyte transfusions has been advocated. Donors must be carefully screened to prevent transmission of infection. In the author's experience, the efficacy of granulocyte transfusions was difficult to prove, and pulmonary sequestration compromise lung severely with marked febrile reactions.

• Interferon-gamma showed no efficacy in one patient (single case report).

See the list below:

• Surgical procedures for leukocyte adhesion deficiency I are of high risk and require flawless postoperative care because of the delayed wound healing and risk for further infection.

• Complications of surgical procedures in leukocyte adhesion deficiency II have not been reported.

See the list below:

• Consultations with surgeons, pulmonologists, and intensivists are often mandatory. The clinical immunologist must work closely with these consultants because the lack of inflammation leads to the underestimation of infection by inexperienced medical personnel.

• Bone marrow transplantation teams are mandatory for therapy of severe leukocyte adhesion deficiency I.

See the list below:

• A normal nutritious diet for age group is appropriate.

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• No restrictions are advised.

• Obviously, care of skin and mucous membranes as portals of entry for infection requires excellent hygiene.

• Injuries are slow to heal and are at high risk for secondary infection.

• Prophylactic antibiotics for injuries are generally used conventionally; the major application is for animal or human bites.

See the list below:

• Bacterial infections require aggressive first-line antibiotic therapy, frequently with intravenous agents.

• Patients with leukocyte adhesion deficiency II can generally be treated as outpatients.

• After initial diagnosis and stabilization, patients with leukocyte adhesion deficiency I can usually complete parenteral antibiotics in the home setting.

See the list below:

• Scrupulous follow-up of infections is necessary for patients with leukocyte adhesion deficiency.

• As noted above, outpatient management of infections has become customary despite the complexity of care and the stress to families.

See the list below:

• Leukocyte adhesion deficiency type I (LAD I) is often associated with life-threatening infections requiring intensive care. Coordinating medical management between immunologists, infectious disease specialists, pulmonologists, and surgical specialists is challenging.

• Excellent laboratory and radiology support mandates hospitalization in tertiary children's medical centers.

See the list below:

• Patients with leukocyte adhesion deficiency I are at risk for fungal infections with Candida species because of their frequent need for broad-spectrum antibiotics.

See the list below:

• Most clinical immunologists strongly believe that the great complexity of medical problems for any primary immunodeficiency disease requires the patient to be managed by an immunologist.

• The subtle signs of infection, the need to offer stem cell transplantation, and the early deaths in patients with leukocyte adhesion deficiency I that is not properly treated suggest that frequent monitoring by a clinical immunologist is essential.

• The major services for transfer are the intensive care and surgical teams.

See the list below:

• Prenatal diagnosis for leukocyte adhesion deficiency I is possible by chorionic villus sampling or amniocentesis using DNA methodology in families where the exact mutations have been established. Fetal blood sampling and fluorocytometric testing for the presence of CD18 on lymphocytes, monocytes, and neutrophils can establish the diagnosis when DNA analysis is not available.

• In leukocyte adhesion deficiency II, ultrasonography for growth retardation, skeletal abnormalities, and distinctive facial features can establish the diagnosis prenatally in some families.

See the list below:

• Patients with leukocyte adhesion deficiency I are at risk for graft versus host disease post–stem cell reconstitution, although graft versus host disease has been less common than in other transplantation settings.

• Patients with leukocyte adhesion deficiency II experience growth failure and mental retardation, although they are less likely to die of infection. Reports of these patients are so rare that other complications may not be observed adequately yet.

See the list below:

• Without hematopoietic stem cell transplantation (HSCT), patients with leukocyte adhesion deficiency I who have an absence of CD18 expression usually die from infection within 2 years of life. The published experience with hematopoietic stem cell transplantation has been excellent with complete immunologic reconstitution. Earlier reviews of leukocyte adhesion deficiency I indicated that unreconstituted patients most often succumbed to bacterial infections. In the author's experience, early recognition and aggressive therapy of bacterial and fungal infections is usually successful. In contrast, no specific therapy is available for the crouplike infections of suspected viral etiology or for aseptic meningitis.

• Patients with leukocyte adhesion deficiency II show severe developmental delay, which has not been significantly prevented even when fucose replacement seemed to decrease infections and improve phagocytic functions.

See the list below:

• The inability to easily detect infection is extremely stressful to families. Aggressive and complicated antibiotic and surgical care may be required for prolonged periods in the home setting, adding further stress.

• Adequate informed consent for stem cell reconstitution must review the high risk for life-threatening infection during the preparative myeloablative regimen in addition to the risk for failure to engraft and graft versus host disease. Although successful complete immune reconstitution from bone marrow transplantation is reported using fully matched related and unrelated donors or haploidentical donors (ie, parents), patients with leukocyte adhesion deficiency I cannot be guaranteed to have benign courses.

• The Immune Deficiency Foundation (some states have local chapters) is an important resource for education and for support for patients and families with any primary immunodeficiency disease. The current address is as follows: 25 W. Chesapeake Ave, Suite 206

• Towson, MD 21204

• Phone number: 877-666-0866

• Web site: www.primaryimmune.org

• The Jeffrey Modell Foundation also provides educational support and raises funds for research. The current address is as follows: 747 3rd Ave

• New York, NY 10017

• Phone: 800-JEFF-844

• Web site: www.jmfworld.org