NO1: an HLA-DQw1-associated determinant present on loss mutants not expressing DQw1.

We have used two monoclonal antibodies, FA and Tu39, and cloned cytotoxic T lymphocytes to study the immunogenetic control of an HLA-D region-encoded determinant(s) recognized by the Tc other than class I or DR or DQ. The Tc recognize a determinant associated with one (the A2) haplotype of LCL721 and are lytic to mutants of LCL 721 that have lost expression of all class I as well as the serologically defined DR and DQw specificities associated with, and presumably identical to, DPw2, the specificity encoded by the sensitizing (A2-B51) haplotype; these data provide the first evidence that FA recognizes the protein dimer presumably expressing the DPw determinant. Those Tc blocked by Tu39 recognized a determinant, referred to as NO1, that is not associated in the population with DPw2, but is found on some, but not all, DQw1-positive cells. We propose three possible explanations for these results. (i) There may be a class II product other than DP or those expressing the DR or DQ serologically defined specificities carrying NO1; such a product could be either as yet undescribed (E. Long has obtained information for an expressed and as yet undefined class II beta gene, personal communication) or a second expressed dimer of the DQ or DP families. (We assume that no DR genes of the A2 haplotype are expressed in these mutants. (ii) NO1 and DPw2 may be on the same molecule; to account for the lack of association of NO1 and DPw2 in the population, one might propose a mechanism such as gene conversion leading to expression of NO1.(ABSTRACT TRUNCATED AT 250 WORDS)