ALLELIC POLYMORPHISM IN THE CODING REGION OF HUMAN TCR-C(ALPHA) GENE AND CHARACTERIZATION OF STRUCTURAL VARIABILITY IN THE ALPHA-CHAIN CONSTANT DOMAIN

An allelic variant of the human TCR C(alpha) gene, designated C(alpha) AL, which encodes a structurally different protein product has been ch aracterized. C(alpha)AL was independently sequenced using polymerase c hain reaction (PCR)-amplified TCR C(alpha) CDNA from various T cell cl ones derived from a same individual. It differed from the most usual C (alpha) sequence by two non-synonymous base changes at codons 4 (AAC-- >AAG) and 84 (GAA-->GCA) of the C(alpha) coding region. These changes imply amino acid substitutions Asn-->Lys and Glu-->Ala respectively. A n oligotyping method, based on hybridization of allele-specific oligon ucleotides to PCR-amplified C(alpha) DNA, is also described. It was us ed for differential typing of the two C(alpha) forms in family and pop ulation studies. In each of three T cell clones analyzed from the same donor having two rearranged TCR alpha chain transcripts, C(alpha)AL w as found in only one of the transcripts. In addition, C(alpha)AL segre gated as a co-dominant mendelian allele within the family of this dono r. Population analysis was carried out in 73 spanish individuals. Twel ve donors (16.4%) were heterozygous, implying that C(alpha)AL was pres ent in this population sample with an allelic frequency of 0.08, The o bserved frequencies of C(alpha) genotypes were those expected for the two alleles being in Hardy -Weinberg equilibrium. This demonstration o f structural polymorphism in the constant region of TCR alpha chains p rovides a useful genetic marker for TCR and disease association studie s due to its precise mapping within the C(alpha) coding region, and it s significant frequency in the analyzed population. In an analysis of 17 multiple sclerosis patients, the distribution of C(alpha) coding re gion alleles was virtually the same as in healthy individuals, indicat ing no preferential association of one C(alpha) coding region allele t o this disease in the population examined.