Monoclonal mouse anti-I-Ak and anti-I-Ek antibodies cross-reacting with HLA-DR supertypic and subtypic determinants rather than classical DR allelic specificities.

Thirty monoclonal alloantibodies (mAB) against mouse Iak antigens have been derived by fusion of mouse myeloma and spleen cells from A.TH (Ks Is Dd) mice immune to A.TL (Ks Ik Dd) lymphoid cells. Analysis of: (i) their reactivity (using 125I labelled protein A cell binding or cytotoxicity assays) on lymphoid cells from selected mouse strains with recombinant H-2 haplotypes; and (ii) the spatial arrangement of the specificities detected on the Iak molecules (studied by means of competitive inhibition of binding of radio-labelled monoclonal antibodies), permitted the identification of various epitopes present either on the I-Ak molecules (some of which were apparently identical to the conventional Ia.2, Ia.1 and Ia.19 specificities), or the I-Ek molecule (some being apparently analogous to the Ia.7 specificity) or on both I-Ak and I-Ek products. These mAB were tested in two different panels of human T and B lymphocytes. Panel (a) consisted of 28 Caucasian unrelated individuals, highly selected with regard to HLA-DR specificities, while panel (b) concerned 53 random HLA-A, B, C, DR typed individuals. The standard complement dependent lymphocytotoxicity microtechnique of histocompatibility workshop VIII was used throughout. All mAB were negative on resting T cells. Testing on B cells produced three patterns: 1) ten mAB did not react with any B cell tested; 2) four mAb reacted with all the panel cells; 3) sixteen mAb reacted with different sets of the panel indicating identification of polymorphic determinants. However, the strength of positivity obtained with a majority of single mAb varied considerably in the panel, suggesting identification of cross-reactive determinants. This necessitated the use of individual assignment criteria for each mAb. Following this procedure, 8 mAb were ascertained as reacting with HLA-DR supertypic determinants, 6 with associations to MT1, MT2, or both. Eight mAb reacted with HLA-DR subtypic determinants (more restricted than a classical DR allele). No mAb were ascertained, reacting exquisitely with acknowledged HLA-DR allelic specificities.