Chemically related antigens compete for presentation by accessory cells to T cells

Immune responsiveness of guinea pigs to dinitrophenyl-poly-L-lysine (DNP-PLL) and to the lysine-rich random copolymer of L-glutamic acid and L-lysine (GL) are both controlled by the "poly-L-lysine gene." We demonstrate that accessory cells of responder strains can be made incapable of presenting DNP-PLL to response T cells in assays for proliferation by in vitro exposure of the cells to GL before and during their exposure to DNP-PLL. The inhibition was not rapidly reversible, because GL preexposed accessory cells that were cultured for 2 hr in GL-free medium were still refractory to pulsing with DNP-PLL. In contrast, DNP-PLL had only a moderate inhibitory effect on accessory cell presentation of GL. Unconjugated poly- and oligo-lysines also inhibited the ability of accessory cells to present DNP-PLL, but inhibitory activity was displayed only by homopolymers containing eight to 12 or more residues in the chain. The homopolymers of D-lysine, L-arginine, and L-glutamic acid, and lysine-free glutamic acid-rich copolymers had little or no inhibitory effect. The results are interpreted to mean that antigens to which responsiveness is regulated by the same Ir gene compete for presentation by accessory cells. This may reflect a competition for the Ir gene product of the antigen-presenting cell.