Accessory cells in immune suppression. II. Evidence for presentation of idiotype-specific suppressor factors to B cell targets by I-A+ accessory cells.

The functional suppression of two BALB/c myelomas, MOPC315 and MOPC460, by idiotype-specific suppressor T cells is mediated by secreted factors (TsF). Idiotype-specific TsF only functions in the presence of accessory cells (AC) that can be low density splenocytes or cells of BALB/c B lymphoma A20-2J. Such AC are I-A+ but do not have to be histocompatible with the myeloma targets or the source of TsF. A20-2J cells incubated with soluble idiotype and TsF also are capable of suppressing the relevant myeloma target. The effect of TsF-pulsed A20-2J cells is idiotype specific, and these cells do not secrete immunosuppressive mediators. Finally, TsF-pulsed A20-2J cells suppress myeloma targets when the two are cultured on the same side of a cell-impermeable membrane but not when they are separated by the membrane. These results indicate that I-A+ cells are capable of concentrating and/or presenting TsF to suppressible targets, and they demonstrate a novel role for Ia-bearing cells in immune regulation.