Ir gene expression on T cells: Effect of a monoclonal antibody directed against I region-controlled determinants on T cells

A monoclonal antibody directed at an I region-controlled epitope uniquely expressed on T cells (Iat) was studied for its in vivo effect on the antibody response under the control of an Ir gene. The antibody was produced by a hybridoma made from A.TH spleen cells immune to A.TL (anti-I^k), that was selected for its reactivity with T but not B cells and macrophages, and thus was designated as anti-Iat^k. The injection of this anti-Iat^k into H-2^k, H-2^b and H-2^k×bF₁ mice resulted in the suppression of antibody response to poly-L-(His,Glu)-poly-D,L -Ala–poly-L -Lys (H,G)-A–L] in H-2^k and F₁ mice but not that to poly-L -(Tyr,Glu)-poly-D,L -Ala–poly-L -Lys (T,G)-A–L] both in H-2^b and F₁ mice. The adoptive cell transfer of the combinations of anti-Iat^k-or normal mouse serum-treated T and B cells into irradiated hosts demonstrated that anti-Iat^k primarily affected (H,G)-A–L-specific helper T cells but not B cells and macrophages, resulting in the specific elimination of the antibody response. Suppressor T cells were not induced by the treatment with anti-Iat^k. The antibody specifically eliminated the (H,G)-A–L-specific but not (T,G)-A–L-specific helper T cells in F₁ spleen cells that had been primed with both (H,G)-A–L and (T,G)-A–L. The results indicated that anti-Iat^k affected the H-2^k-associated Ir gene function born by T cells but not by antigen-presenting cells, which was expressed on F₁ helper T cells with apparent exclusion of the other allele, and implied that the Iat antigen on helper T cells is one of the sites of expression of Ir genes.