Close Association of Human Mixed Lymphocyte Culture Antigen, Ia-Like Antigen and Fc Receptor

The effects of aggregated human IgG, human anti-Ia-like antibody, and anti-β2-microglobulin on mixed lymphocyte culture (MLC) were studied. Aggregated human IgG inhibited both stimulatory and responding activities in MLC. When Fc-receptor-bearing cells were removed from responding cells, the inhibitory activity of aggregated IgG was markedly reduced. The result suggested that the inhibition of MLC by aggregated IgG is primarily based on the blocking of Fc-receptor-bearing cells contained in the stimulator cells. In addition, the removal of Fc-receptor-bearing cells from stimulatory cells resulted in the loss of MLC response. Anti-Ia-like antibodies contained in anti-HLA sera and B-cell-specific human alloanti-sera also inhibited stimulatory activities in MLC. Rabbit antiserum against human β2-micro-globulin showed inhibitions of both stimulatory and responding activities. These results suggested the close association of human MLC stimulator site with Fc receptor and Ia-like antigen and also some relation of β2-microglobulin with MLC reaction.