The human ‘T’ genetic region of the HLA linkage group is a polymorphism detected on lectin-activated lymphocytes

Abstract

The major histocompatibility complex of the mouse, H–2, comprises 12 loci which are grouped into regions and subregions¹. Present data indicate that to the ‘right’ of the H–2D there are nine loci clustered into one region, the ‘T region’. These loci are designated Qa-1, Qa-2, Qa-3, Qa-4, Qa-5, H–2T, H–31, H–32, TLa (ref. 2). The loci in the ‘T region’ may, in fact, be part of the H–2 complex. This notion is supported by the fact that gene products of the TLa, Qa-2 and Qa-3 loci share some molecular properties with H–2 products: a two-polypeptide chain complex with a common determinant of molecular weight 12,000 β₂-microglobulin and a variable heavy chain of MW 45,000 (ref. 3). Recent reports suggested the possible existence of human analogues to the gene products of the murine ‘T region’. Antigenic structures, similar but not identical with HLA-A, -B and -C antigens, were recently isolated from the human lymphoblastoid T-cell line MOLT4 (refs 4,5). These reports presented evidence for the existence of a β₂-microglobulin or a β₂-microglobulin-like molecule, Bt, associated with a polypeptide chain of MW∼45,000. However, it remains to be determined whether these structures are equivalent to the mouse Qa-1, Qa-2 or TLa gene products. We now report the identification of human alloantisera that react with cell-surface determinants expressed on mitogen-activated T lymphocytes but not expressed on resting T cells. Antigen blocking and modulation techniques were used. The alloantigens identified (HT) are different from the classical HLA-A, -B, -C and -DR antigens but are associated with β₂-microglobulin. These determinants are encoded by genes in the HLA-A region and may represent the human counterpart of the TLa region determinants of the mouse^1–3.