SUMMARY
1. Leukocyte adhesion deficiency (LAD) is an autosomal recessive primary immunodeficiency characterized by a defect in neutrophil adhesion to the vessel endothelium. As a result, neutrophils are unable to leave the vasculature to migrate to sites of inflammation or infection. Total neutrophil number and function are normal.
2. Neutrophil migration from blood vessels to the extravascular space occurs by a number of sequential steps:
Leukocyte Rolling - Loose adhesion to vessel wall is mediated by selectin binding.
Leukocyte Activation - Integrins are activated and undergo conformational change.
Leukocyte Firm Adhesion - Activated integrins mediate firm binding to the vessel wall.
Leukocyte Transmigration - Leukocytes migrate between endothelial cells and exit the vasculature.
3. Three genetic forms of LAD have been described:
Leukocyte Adhesion Deficiency 1
a. LAD 1 is the most common type of LAD and is caused by a deficiency or defect in the common beta chain of the beta 2-integrin family CD18. This leads to impaired firm adhesion of leukocytes.
b. LAD 1 is characterized by the following clinical features:
Delayed separation of the umbilical cord (normal separation is 3-45 days with a mean of 10 days) with concurrent omphalitis.
Leukocytosis (50,000 - 100,000/ul) even in the absence of infection due to impaired mobilization to extravascular sites.
Recurrent bacterial skin infections, sepsis and pneumonia (staphylococcus and gram negative bacilli)
Absent pus formation at the site of infection inflammation is devoid of neutrophils
Impaired wound healing
Severe gingivitis and periodontal disease (later in life)
c. The prognosis for patients depends on the degree of CD18 deficiency that is present. A severe phenotype occurs when less than 2% of normal CD18 surface expression is present (patients suffer early infections and often die during infancy). A mild to moderate phenotype occurs when CD18 expression is 2-30% of normal patients manifest fewer serious infections and typically survive into adulthood. However, it should be noted that only 25% of the patients with the milder phenotype survive beyond 40 years.
d. This disease should be considered in any infant (male or female) with recurrent skin and lung infections, delayed umbilical cord separation and omphalitis, and a very high leukocyte count on a CBC.
e. The diagnosis is confirmed by demonstrating a reduced or absent surface expression of CD18 and CD11 by flow cytometry. Sequencing of the beta 2 integrin gene (ITGB2) would provide a definitive diagnosis.
f. The cornerstone of therapy remains prompt and aggressive treatment of infections with appropriate antibiotics. G-CSF is not helpful as this medication would increase neutrophil number but they would still be unable to transmigrate across the vascular endothelium.
g. Hematopoietic Stem Cell Transplantation should be a consideration for patients with a severe LAD 1 phenotype given their short life expectancy. The success rate of matched transplants is approximately 80% while the success rate of haploidentical transplants is only 50%. Success with use of reduced intensity conditioning regimens has been reported.
Leukocyte Adhesion Deficiency 2
a. LAD 2 is caused by mutations in the gene which encodes the GDP-fucose transporter 1 (FUCT1). This leads to an absence of fucosylated carbohydrate ligands (which bind selectins on the endothelium) resulting in defective leukocyte rolling. LAD 2 neutrophils are still able to adhere and transmigrate via beta 2-integrins under conditions of reduced shear forces. Fewer than 10 patients with LAD 2 have been reported.
b. The clinical features of LAD 2 are generally less severe than LAD 1 and are summarized below:
There is NO delayed separation of the umbilical cord
Leukocytosis (10,000 - 40,000/ul) is present
Bacterial skin and lung infections are generally non life-threatening
Pus formation is impaired but not absent
Bombay (hh) blood group - there is an absence of the H antigen on RBCs, which is a fucose carbohydrate. This requires specialized testing for detection (standard testing will report blood type as O).
Severe mental retardation, motor delay, microcephaly, and growth retardation
c. The absence of CD15a (SLeX) on the surface of leukocytes by flow cytometry suggests the diagnosis. CD15a is a glycan that incoporporates fucose and is normally expressed on leukocytes.
d. The definitive diagnosis is established by sequence analysis of the GDP-fucose transporter 1 gene (FUCT1).
e. Treatment involves aggressive management of bacterial infections with antibiotics. Prophylactic antibiotic therapy (ex. trimethoprim-sulfamethoxazole) is also an option. Infectious complications tend to decrease with age. Fucose supplementation should be started as early as this therapy may help prevent psychomotor retardation.
Leukocyte Adhesion Deficiency 3
a. In LAD 3, integrin expression and structure is intact but integrin activation (and thus binding) is defective. Mutations in Kindlin-3 (an integrin adaptor protein) have been reported in patients with LAD 3. Defects in calcium-diacylglycerol guanine nucleotide exchange factor I (CalDAG GEF1) cause a syndrome resembling LAD 3 in a mouse model but the significance of this mutation in humans is not clear.
b. The clinical phenotype of LAD 3 is similar to LAD 1 with leukocytosis, delayed separation of the umbilical cord, and severe life-threatening bacterial infections. Platelet aggregation dysfunction also leads to bleeding complications such as cerebral hemorrhage, hematuria and bloody stools.
c. This diagnosis should be considered in patients who have a LAD 1 phenotype but have normal CD18 surface expression. The diagnosis requires demonstration of impaired integrin activation. Genetic analysis for KINDLIN3 mutations should be performed for all suspected cases.
d. As with LAD 1, the prognosis is quite poor unless a HSCT is performed early in infancy.
OVERVIEW
1. Leukocyte adhesion deficiency (LAD) is an autosomal recessive primary immunodeficiency characterized by a defect in neutrophil adhesion to the vessel endothelium. As a result, neutrophils are unable to leave the vasculature to migrate to sites of inflammation or infection. Total neutrophil number and function are normal.
2. Neutrophil migration from blood vessels to the extravascular space occurs by a number of sequential steps:
Leukocyte Rolling - Loose adhesion to vessel wall is mediated by selectin binding.
Leukocyte Activation - Integrins are activated and undergo conformational change.
Leukocyte Firm Adhesion - Activated integrins mediate firm binding to the vessel wall.
Leukocyte Transmigration - Leukocytes migrate between endothelial cells and exit the vasculature.
3. Three genetic forms of LAD have been described:
Leukocyte Adhesion Deficiency 1
a. LAD 1 is the most common type of LAD and is caused by a deficiency or defect in the common beta chain of the beta 2-integrin family CD18. This leads to impaired firm adhesion of leukocytes.
b. LAD 1 is characterized by the following clinical features:
Delayed separation of the umbilical cord (normal separation is 3-45 days with a mean of 10 days) with concurrent omphalitis.
Leukocytosis (50,000 - 100,000/ul) even in the absence of infection due to impaired mobilization to extravascular sites.
Recurrent bacterial skin infections, sepsis and pneumonia (staphylococcus and gram negative bacilli)
Absent pus formation at the site of infection inflammation is devoid of neutrophils
Impaired wound healing
Severe gingivitis and periodontal disease (later in life)
c. The prognosis for patients depends on the degree of CD18 deficiency that is present. A severe phenotype occurs when less than 2% of normal CD18 surface expression is present (patients suffer early infections and often die during infancy). A mild to moderate phenotype occurs when CD18 expression is 2-30% of normal patients manifest fewer serious infections and typically survive into adulthood. However, it should be noted that only 25% of the patients with the milder phenotype survive beyond 40 years.
d. This disease should be considered in any infant (male or female) with recurrent skin and lung infections, delayed umbilical cord separation and omphalitis, and a very high leukocyte count on a CBC.
e. The diagnosis is confirmed by demonstrating a reduced or absent surface expression of CD18 and CD11 by flow cytometry. Sequencing of the beta 2 integrin gene (ITGB2) would provide a definitive diagnosis.
f. The cornerstone of therapy remains prompt and aggressive treatment of infections with appropriate antibiotics. G-CSF is not helpful as this medication would increase neutrophil number but they would still be unable to transmigrate across the vascular endothelium.
g. Hematopoietic Stem Cell Transplantation should be a consideration for patients with a severe LAD 1 phenotype given their short life expectancy. The success rate of matched transplants is approximately 80% while the success rate of haploidentical transplants is only 50%. Success with use of reduced intensity conditioning regimens has been reported.
Leukocyte Adhesion Deficiency 2
a. LAD 2 is caused by mutations in the gene which encodes the GDP-fucose transporter 1 (FUCT1). This leads to an absence of fucosylated carbohydrate ligands (which bind selectins on the endothelium) resulting in defective leukocyte rolling. LAD 2 neutrophils are still able to adhere and transmigrate via beta 2-integrins under conditions of reduced shear forces. Fewer than 10 patients with LAD 2 have been reported.
b. The clinical features of LAD 2 are generally less severe than LAD 1 and are summarized below:
There is NO delayed separation of the umbilical cord
Leukocytosis (10,000 - 40,000/ul) is present
Bacterial skin and lung infections are generally non life-threatening
Pus formation is impaired but not absent
Bombay (hh) blood group - there is an absence of the H antigen on RBCs, which is a fucose carbohydrate. This requires specialized testing for detection (standard testing will report blood type as O).
Severe mental retardation, motor delay, microcephaly, and growth retardation
c. The absence of CD15a (SLeX) on the surface of leukocytes by flow cytometry suggests the diagnosis. CD15a is a glycan that incoporporates fucose and is normally expressed on leukocytes.
d. The definitive diagnosis is established by sequence analysis of the GDP-fucose transporter 1 gene (FUCT1).
e. Treatment involves aggressive management of bacterial infections with antibiotics. Prophylactic antibiotic therapy (ex. trimethoprim-sulfamethoxazole) is also an option. Infectious complications tend to decrease with age. Fucose supplementation should be started as early as this therapy may help prevent psychomotor retardation.
Leukocyte Adhesion Deficiency 3
a. In LAD 3, integrin expression and structure is intact but integrin activation (and thus binding) is defective. Mutations in Kindlin-3 (an integrin adaptor protein) have been reported in patients with LAD 3. Defects in calcium-diacylglycerol guanine nucleotide exchange factor I (CalDAG GEF1) cause a syndrome resembling LAD 3 in a mouse model but the significance of this mutation in humans is not clear.
b. The clinical phenotype of LAD 3 is similar to LAD 1 with leukocytosis, delayed separation of the umbilical cord, and severe life-threatening bacterial infections. Platelet aggregation dysfunction also leads to bleeding complications such as cerebral hemorrhage, hematuria and bloody stools.
c. This diagnosis should be considered in patients who have a LAD 1 phenotype but have normal CD18 surface expression. The diagnosis requires demonstration of impaired integrin activation. Genetic analysis for KINDLIN3 mutations should be performed for all suspected cases.
d. As with LAD 1, the prognosis is quite poor unless a HSCT is performed early in infancy.
EVALUATION
Step 1: Initial Immune Evaluation
A broad initial immune evaluation is recommended (particularly in infants) to screen for severe combined immune deficiency (SCID), combined immune deficiencies and chronic granulomatous disease diseases which can present early in life with severe bacterial infections. The following tests would typically be normal in LAD with the exception of an elevated white blood cell count (due to neutrophilia) even in the absence of infection.
CBC with Differential
Quantitative immunoglobulins (IgG, IgM, IgA)
Antibody titers to vaccine antigens
Lymphocyte flow cytometry for B-cell subpopulations
Flow cytometry for B cell, T cell, and NK cell enumeration
T cell proliferation to mitogens
DHR assay (or NBT test)
Step 2: Evaluation of surface integrin expression (for LAD 1 - most common)
CD18 and CD11 flow cytometry
CD18 expression will be very decreased or absent in LAD 1 but will be normal in LAD II or LAD III
Step 3: Additional testing for suspected LAD 2
CD15a flow cytometry
Analysis for Bombay (hh) blood phenotype
CD15a (SLeX) is a fucose containing glycan that is absent on the surface of LAD 2 leukocytes.
Red blood cells from LAD 2 patients have a rare Bombay (hh) phenotype with absence of the H antigen. This cannot be detected by standard blood type testing the sample will be reported as O blood type.
Step 4: Additional testing for suspected LAD 3
Integrin Activation Assay
This test is available at specialized research centers.
Step 5: Gene Sequencing
LAD 1: ITGB2 gene - encodes CD18
LAD 2: SLC35C1 gene - encodes GDP-fucose transporter 1
LAD 3: KINDLIN3 gene
Identification of gene mutations would provide a definitive diagnosis as well as valuable data for genetic counseling. ITGB2 sequencing is commercially available through gene dx. LAD 2 and LAD 3 genetic testing is only available at specialized research centers.
MANAGEMENT
LAD 1: The cornerstone of therapy remains prompt and aggressive treatment of infections with appropriate antibiotics. G-CSF is not helpful as this medication would increase neutrophil number but they would still be unable to transmigrate across the vascular endothelium.
Hematopoietic Stem Cell Transplantation (HSCT) should be a consideration for patients with a severe LAD 1 phenotype given the short life expectancy. The success rate of matched transplants is approximately 80% while the success rate of haploidentical transplants is only 50%. Success with use of reduced intensity conditioning regimens has been reported.
LAD 2: Treatment involves aggressive treatment of bacterial infections. Prophylactic antibiotic therapy (ex. trimethoprim-sulfamethoxazole) is also an option. Infectious complications tend to decrease with age. Fucose supplementation should be started as early as this therapy may help prevent psychomotor retardation.
LAD 3: The management is similar to LAD 1 with prompt treatment of bacterial infections and consideration for HSCT given the high mortality during infancy.
RESOURCES
Diagnostic Resources
1. Leukocyte adhesion deficiency (LAD, type 1)
- Cincinnati : Flow cytometry
- Seattle's Children: Sequencing
2. Leukocyte adhesion deficiency (LAD, type 2)
Literature Resources
1. Etzioni 2010
LAD Review
2. Qasim 2009
HSCT for LAD I (36 patients)
3. Svensson 2009
LAD 3 is caused by mutations in KINDLIN3 affecting integrin activation
4. Uzel 2001
A case of LAD I and colitis
5. D'Agata 1996
LAD presenting as chronic ileocolitis