Induction of antibodies by blood transfusions capable of inhibiting responses in MLC.

B6AF1 (H-2KbkDbd) mice were transfused weekly with 0.1 ml of whole blood from DBA/2 (H-2d) mice. One week after each transfusion, the mice were bled and the sera were collected and pooled. The presence of antiidiotypic antibodies in these sera was investigated using the mixed-lymphocyte culture (MLC) inhibition test, in which spleen cells from normal B6AF1 mice were treated with sera from transfused B6AF1 mice, washed, and then tested for their responses to DBA/2 stimulator cells. The sera collected following 3 and 4 transfusions caused a significant inhibition of responses in MLC, but sera obtained after 1 and 2 transfusions caused little or no inhibition. This inhibition was specific for stimulator cells from the blood donor (DBA/2) and was not observed against third-party SJL (H-2s) stimulator cells. In addition, the suppressive effect in MLC was specific for responder cells from the recipient B6AF1 mice, and no suppression was observed with responder cells from C3H (H-2k) and SJL mice. Treatment of DBA/2 stimulator cells with the serum caused no inhibition in MLC. The MLC inhibitory activity of the serum decreased gradually from the first to the third week following 4 transfusions, although a significant inhibition was still demonstrable after 3 weeks. These findings suggest that multiple blood transfusions induce antiidiotypic antibodies that can block the T cell antigen-specific receptors and cause suppression of the recipient's responses against the donor's alloantigens in MLC.