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

Abstract

Thirty monoclonal alloantibodies (mAB) against mouse Ia^k antigens have been derived by fusion of mouse myeloma and spleen cells from A.TH (K^s I^s D^d) mice immune to A.TL (K^s I^k D^d) 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 Ia^k 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-A^k molecules (some of which were apparently identical to the conventional Ia. 2, Ia. 1 and Ia. 19 specificities), or the I-E^k molecule (some being apparently analogous to the Ia.7 specificity) or on both I-A^k and I-E^k 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 exquisitly with acknowledged HLA-DR allelic specificities.