1/5. A novel CD18 genomic deletion in a patient with severe leucocyte adhesion deficiency: a possible CD2/lymphocyte function-associated antigen-1 functional association in humans.Leucocyte adhesion deficiency (LAD) is an autosomal-recessive genetic disease that is characterized clinically by severe bacterial infections and caused by mutations in the CD18 gene that codes for the beta2 integrin subunit. A patient with a severe LAD phenotype was studied and the molecular basis of the disease was identified as a single homozygous defect in a Herpes virus saimiri (HVS)-transformed T-cell line. The defect identified involves a deletion of 171 bp in the cDNA that encodes part of the proteic extracellular domain. This genetic abnormality was further studied at the genomic dna level and found to consist of a deletion of 169 bp (from -37 of intron 4 to 132 of exon 5), which abolishes the normal splicing and results in the total skipping of exon 5. The 171-bp shortened 'in-frame' mRNA not only resulted in the absence of CD18 expression on the cell surface but also in its absence in the cytoplasm of HVS T-cell lines. Functionally, the LAD-derived HVS T-cell lines showed a severe, selective T-cell activation impairment in the CD2 (but not in the CD3) pathway. This defect was not reversible when exogenous interleukin-2 (IL-2) was added, suggesting that there is also a functional interaction of the lymphocyte function-associated antigen-1 (LFA-1) protein in the CD2 signal transduction pathway in human T cells, as has been previously reported in mice and in the human Papillon-Lefevre syndrome. Thus, HVS transformation is not only a suitable model for T-cell immunodeficiency studies and characterization, but is also a good system for investigating the immune system in pathological conditions. It may also be used in the future in cellular models for in vitro gene-therapy trials.- - - - - - - - - - ranking = 1keywords = antigen (Clic here for more details about this article) |
2/5. Insights into leukocyte adhesion deficiency type 2 from a novel mutation in the GDP-fucose transporter gene.Leukocyte adhesion deficiency type 2 (LADII) is characterized by defective selectin ligand formation, recurrent infection, and mental retardation. This rare syndrome has only been described in 2 kindreds of Middle Eastern descent who have differentially responded to exogenous fucose treatment. The molecular defect was recently ascribed to single and distinct missense mutations in a putative Golgi guanosine diphosphate (GDP)-fucose transporter. Here, we describe a patient of Brazilian origin with features of LADII. Sequencing of the GDP-fucose transporter revealed a novel single nucleotide deletion producing a shift in the open-reading frame and severe truncation of the polypeptide. Overexpression of the mutant protein in the patient's fibroblasts did not rescue fucosylation, suggesting that the deletion ablated the activity of the transporter. Administration of oral L-fucose to the patient produced molecular and clinical responses, as measured by the appearance of selectin ligands, normalization of neutrophil counts, and prevention of infectious recurrence. The lower neutrophil counts paralleled improved neutrophil interactions with activated endothelium in cremasteric venules of nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. However, fucose supplementation induced autoimmune neutropenia and the appearance of H antigen on erythrocytes, albeit without evidence of intravascular hemolysis. The robust response to fucose despite a severely truncated transporter suggests alternative means to transport GDP-fucose into the Golgi complex.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
3/5. A novel genetic leukocyte adhesion deficiency in subsecond triggering of integrin avidity by endothelial chemokines results in impaired leukocyte arrest on vascular endothelium under shear flow.Leukocyte arrest on vascular endothelium under disruptive shear flow is a multistep process that requires in situ integrin activation on the leukocyte surface by endothelium-displayed chemoattractants, primarily chemokines. A genetic deficiency of leukocyte adhesion to endothelium associated with defective beta2 integrin expression or function (LAD-1) has been described. We now report a novel severe genetic disorder in this multistep process associated with functional defects in multiple leukocyte integrins, reflected in recurrent infections, profound leukocytosis, and a bleeding tendency. This syndrome is associated with an impaired ability of neutrophil and lymphocyte beta1 and beta2 integrins to generate high avidity to their endothelial ligands and arrest cells on vascular endothelium in response to endothelial chemoattractant signals. Patient leukocytes roll normally on endothelial selectins, express intact integrins and G protein-coupled chemokine receptors (GPCR), spread on integrin ligands, and migrate normally along a chemotactic gradient. Activation of beta2 integrins in response to GPCR signals and intrinsic soluble ligand binding properties of the very late activation antigen-4 (VLA-4) integrin are also retained in patient leukocytes. Nevertheless, all integrins fail to generate firm adhesion to immobilized ligands in response to in situ GPCR-mediated activation by chemokines or chemoattractants, a result of a primary defect in integrin rearrangement at ligand-bearing contacts. This syndrome is the first example of a human integrin-activation deficiency associated with defective GPCR stimulation of integrin avidity at subsecond contacts, a key step in leukocyte arrest on vascular endothelium under shear flow.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
4/5. chemotaxis of non-compressed blood polymorphonuclear leukocytes from an adolescent with severe leukocyte adhesion deficiency.We have defined the defect in a child with severe leukocyte adhesion deficiency-1 (LAD) as resulting from a single amino acid shift in CD18 (from a C to T mutation at position 533) that prevents heterodimerization with the CD11 antigens to produce beta(2) integrins-the first reported patient homozygous for this defect. Although beset by frequent infections, the patient has survived to adolescence despite the lack of these important adhesion molecules. Consistent with his clinical course is the ability of his PMN to respond chemotactically in slide preparations, albeit with difficulty because of their poor purchase on substrate. The operant adhesins are unknown; his polymorphonuclear leukocytes (PMN) remain chemotactically responsive in the presence of antibodies to alphavbeta(3) and beta(1) integrins and to integrin-associated protein (IAP). These findings indicate that not all patients with severe LAD are candidates for early bone marrow transplantation.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
5/5. Unique CD18 mutations involving a deletion in the extracellular stalk region and a major truncation of the cytoplasmic domain in a patient with leukocyte adhesion deficiency type 1.Two novel CD18 mutations were identified in a patient who was a compound heterozygote with type 1 leukocyte adhesion deficiency and whose phenotype was typical except that he exhibited hypertrophic scarring. A deletion of 36 nucleotides in exon 12 (1622del36) predicted the net loss of 12 amino acid (aa) residues in the third cysteine-rich repeat of the extracellular stalk region (mut-1). A nonsense mutation in exon 15 (2200G>T), predicted a 36-aa truncation of the cytoplasmic domain (mut-2). Lymphocyte function-associated antigen 1 (LFA-1) and macrophage antigen-1 (Mac-1) containing the mut-1 beta(2) subunit were expressed at very low levels compared with wild-type (wt) beta(2). Mac-1 and LFA-1 expression with the mut-2 beta(2) subunit were equivalent to results with wt beta(2). Binding function of Mac-1 with mut-2 beta(2) was equivalent to that with wt beta(2). However, binding function of LFA-1 with the mut-2 beta(2) subunit was reduced by 50% versus wt beta(2). It was concluded that (1) the portion of the CD18 stalk region deleted in mut-1 is critical for beta(2) integrin heterodimer expression but the portion of the cytoplasmic domain truncated in mut-2 is not; and (2) the mut-2 cytoplasmic domain truncation impairs binding function of LFA-1 but not of Mac-1. Studies with the patient's neutrophils (PMNs) were consistent with functional impairment of LFA-1 but not of Mac-1.- - - - - - - - - - ranking = 0.4keywords = antigen (Clic here for more details about this article) |