Multiple functional sites on a single Ia molecule defined using T cell clones and antibodies with chain-determined specificity.

Abstract

Monoclonal antibodies (mAb) were used to inhibit the proliferation of antigen-reactive (C57BL6/J X A/J)F1 restricted T cell clones. We have been able to subdivide these F1 restricted T cell clones into two groups: one of which recognizes the A alpha k A beta b molecule and the other group which recognizes the A alpha b A beta k molecule. Using clones with defined reactivities, we could assign the reactivities of monoclonals to the A alpha or A beta chains. By immunoprecipitation and two-dimensional analysis of Ia molecules from F1 spleen cells, we could independently map the reactivities of the mAb as being determined by the A alpha or A beta chain. To date, these two methods of chain localization of the antibody reactivity have agreed. Further, the differential blocking of the A alpha k A beta b restricted T cell clones suggests that there exists more than one restriction site per Ia molecule. Increasing the number of possible functional Ia restriction sites, either through combinatorial association of alpha and beta chains or by using more than one site per molecule, should increase the number of ways Ia molecules can function in antigen presentation.

A molecular basis for the Ia.2 and Ia.19 antigenic determinants.

“…Finally, competitive binding assays with pairs of anti-Ia mAbs have revealed that the A and E complexes contain several partially or non-overlapping epitopes (11,12). Parallel Ab-blocking studies with these mAbs have shown that T cells, too, are capable of distinguishing several epitopes on an Ia molecule (8,9,13). In summary, it seems that the understanding of what a T cell "sees" on an Ia antigen has increased in parallel with our ability to precisely assign Ia determinants.…”

“…More recently, however, the response to poly(Glu6WAlaIOTyrlO) has been studied for isolated T-cell clones and the results appear somewhat different (13 (8,9). An earlier report had placed a component of Ia.2 on Ap because of its ability to precipitate the isolated chain (7), but the significance of this contradiction is unclear since none of the mAbs could precipitate the isolated Aa chain and since the specificity assignment of the anti-Ia.2 used in these experiments is now doubtful (25 that Arg-57 and Glu-75 lie within T-cell restriction sites on the Aa chain.…”

“…Recently, it has been possible to assign certain of the Ia determinants to specific chains on the basis of a mAb's ability to precipitate isolated or hybrid chains (7)(8)(9)(10). Blocking experiments using these reagents have revealed that both the a and ,3 chains can restrict T cells (8,9).…”

“…Notably, Pierres et (8,9). We have previously sequenced six A, alleles-k, b, d, f, q, and u-thus providing a strong data base for correlative studies (15 (18).…”

“…Recently, it has been possible to assign certain of the Ia determinants to specific chains on the basis of a mAb's ability to precipitate isolated or hybrid chains (7)(8)(9)(10). Blocking experiments using these reagents have revealed that both the a and ,3 chains can restrict T cells (8,9). Finally, competitive binding assays with pairs of anti-Ia mAbs have revealed that the A and E complexes contain several partially or non-overlapping epitopes (11,12).…”