ABSTRACT
Recently, a linkage of the chromosomal region 19q13.4 with bronchial asthma has been demonstrated. This region harbours the so-called leucocyte receptor cluster with the gene for immunoglobulin-like-transcript 3 (ILT3) as a member. ILT3 represents an inhibitory receptor bearing three immunoreceptor tyrosine inhibitory motifs (ITIM). The protein mediates downregulation of cell activation through recruitment of different SH2-containing protein tyrosine phosphatases. With regard to the negative immunoregulatory function particularly on B-cells, ILT3 represents a candidate gene for atopy and asthma. The aim of this study was to screen for common polymorphisms in the gene coding for ILT3 and to test for association with the atopic phenotype. Using single-stranded conformal polymorphism-analysis and direct genomic sequencing seven polymorphisms, three mutations, a common deletion of 7 bp in the third intron and evidence for further alternative splicing of the ILT3 gene were found. Although no association was found with atopy phenotypes, it might prove useful to test for association with bronchial asthma.
Subject(s)
Hypersensitivity, Immediate/genetics , Polymorphism, Genetic/genetics , Receptors, Cell Surface , Receptors, Immunologic/genetics , Receptors, Immunologic/immunology , Adolescent , Adult , Alleles , Alternative Splicing/genetics , Alternative Splicing/immunology , Child , Child, Preschool , Exons/genetics , Exons/immunology , Gene Frequency , Humans , Hypersensitivity, Immediate/immunology , Linkage Disequilibrium/genetics , Linkage Disequilibrium/immunology , Membrane Glycoproteins , Polymorphism, Genetic/immunology , Polymorphism, Restriction Fragment Length , Polymorphism, Single-Stranded Conformational , Receptors, Immunologic/bloodABSTRACT
The platelet-activating factor (PAF) represents a phospholipid with complex biological functions, including involvement in inflammatory processes. The degrading enzyme PAF acetylhydrolase (PAFAH) represents a candidate for asthma and other atopic diseases. Two loss-of-function mutations of PAFAH are associated with severe asthma in Japanese individuals. Our aim was to look for further PAFAH variants in white populations, their possible association with atopic and asthmatic phenotypes, and their functional importance. We picked up three common variants in the PAFAH gene: Arg92His (exon 4), Ile198Thr (exon 7), and Ala379Val (exon 11). The known loss-of-function mutations were not seen. The variant allele Thr198 was found to be highly associated with total IgE concentrations in an atopic population (P=.009) and with "atopic asthma" in an asthmatic population (P=.008). The variant allele Val379 was found to be highly associated with "specific sensitization" in the atopic population (P=.002) and with "asthma" in the asthmatic population (P=.003). By use of recombinant PAFAH enzymes, the variant Val379 showed increased (14 microM) and Thr198 markedly increased (42 microM) KM values compared to the wild type (7 microM); furthermore, Vmax of Val379 was highly increased (132%). Thr198 and Val379 influence plasmatic PAFAH toward lower substrate affinities and therefore are very likely to prolong the activities of PAF. At the same time, they are associated with an increased risk to develop asthma and atopy. Thus, two PAFAH variants seem to play a key role in atopic and asthmatic processes in Caucasian populations.
Subject(s)
Amino Acid Substitution/genetics , Asthma/genetics , Hypersensitivity, Immediate/genetics , Mutation/genetics , Phospholipases A/genetics , Phospholipases A/metabolism , 1-Alkyl-2-acetylglycerophosphocholine Esterase , Adolescent , Adult , Alleles , Asthma/enzymology , Asthma/immunology , Case-Control Studies , Catalysis , Child , Exons/genetics , Gene Frequency/genetics , Genetic Predisposition to Disease/genetics , Genetic Variation/genetics , Humans , Hypersensitivity, Immediate/enzymology , Hypersensitivity, Immediate/immunology , Immunoglobulin E/analysis , Kinetics , Linkage Disequilibrium/genetics , Phenotype , Phospholipases A/antagonists & inhibitors , Phospholipases A/isolation & purification , Polymorphism, Genetic/genetics , Recombinant Proteins/antagonists & inhibitors , Recombinant Proteins/genetics , Recombinant Proteins/isolation & purification , Recombinant Proteins/metabolism , White People/geneticsABSTRACT
BACKGROUND: beta-Lactoglobulin (BLG) represents one of the major allergens causing cow's milk allergy (CMA) - a disease with a wide spectrum of clinical symptoms. The aim of this study was to evaluate sequential B cell epitopes of BLG by the Pin-ELISA method. Furthermore, we wanted to investigate a possible association of the IgE recognition patterns in sera of patients with BLG sensitization and the type of clinical reactions following contact with cow's milk. METHODS: Overlapping sequential decapeptides corresponding to the amino acid sequence of BLG were used in Pin-ELISAs specific for human IgE. Tested sera were from 14 individuals with CMA, 8 of them with a history of immediate systemic reactions and 6 with delayed skin reactions following contact with cow's milk. All of them showed specific IgE antibodies to BLG in the CAP-RAST. Control sera were from 5 healthy nonallergic individuals. RESULTS: All sera from BLG-sensitized individuals showed IgE binding with one region of BLG corresponding to amino acids 95-113. Furthermore, individual sera showed reactions with two further regions, 12-27 and 124-135. Inhibition of IgE binding to BLG with one soluble synthetic peptide confirmed the major epitope. No differences were found in the B cell epitope recognition pattern to BLG in the two groups of patients with CMA, characterized by acute systemic or delayed skin reactions. CONCLUSIONS: Using IgE Pin-ELISAs we were able to confirm previously described sequential B cell epitopes of BLG. However, the recognition pattern of one of the major cow's milk allergens is not predictive of the clinical type of reaction.
