| Abstract: | Influenza-specific cytotoxic T cells restricted by HLA-A3 and allogeneic CTL specific for HLA-A3 recognize differences between serologically indistinguishable HLA-A3 antigens. Previous biochemical studies have indicated that such differential recognition can be explained by alterations in the primary structure of class I heavy chains. Characterization of these sequence differences may therefore identify portions of the class I molecule that form determinants recognized by CTL. In this study, we describe the cloning and sequencing of an HLA-A3 subtype from donor E1 (E1-A3). Cloning of the gene encoding E1-A3 was simplified by determining that a 15.5-kb BamHI fragment contains the complete gene and is characteristic of HLA-A3 and only one other class I gene (HLA-A11). Comparison of the E1-A3 sequence to that of a previously sequenced HLA-A3 gene for exons encoding extracellular class I domains revealed three nucleotide differences. All of these differences were located within a discrete region of exon 3 (encoding the alpha 2 domain) and result in a change of two amino acids, at positions 152 (Glu----Val) and 156 (Leu----Gln). This finding suggests that these amino acids are crucial for the information of a determinant recognized by CTL. Furthermore, the altered nucleotide sequence of E1-A3 is identical to the sequence of the HLA-Aw24 gene for codons 128 to 161. These observations of multiple clustered changes in the E1-A3 subtype (relative to the prototype sequence) and identity of the altered sequence with the sequence of another class I gene support the concept that gene conversion is a primary mechanism for the generation of class I polymorphism. |
