Characterization of a product of histoincompatible spleen cells restoring class I-inhibited mixed-lymphocyte culture reactions

Reconstitution of primary mixed-lymphocyte culture reactions inhibited with class I antibodies by a product of histoincompatible spleen cells

Primary MLC reactions with spleen cells from mice of conventional inbred or congenic origin and incompatible at the entire H-2 or at K- or D-regions could be inhibited by pretreating stimulator but not responder cells with mAb to Class I MHC antigens. Inhibited MLC reactions, initiated in the presence of a product (SEPIR) present in supernatants after short-term cultivations of one-way histoincompatible spleen cells of the same haplotype as MLC cells, could be restored specifically to normal activities. It is suggested that the reconstituting factor represents a product of Class I antigen recognition capable of compensating the prevented recognition of these antigens by MLC responder cells. SEPIR was ineffective in restoring Class II antigen-inhibited MLC responses. Because the product might be formed spontaneously under normal MLC conditions, it had no effect when added to uninhibited MLC cells. Conceivably due to neutralization, SEPIR was also incapable of restoring MLC responses conducted in the continuous presence of Class I mAb. Inhibition of MLC responses and reconstitution with SEPIR depended on the effectiveness of Class I antigen inhibition.