Cellular and humoral factors governing canine mixed lymphocyte cultures after renal transplantation: IV second-set transplants and cytophilic antibody

Continuing studies of cellular and humoral factors influencing the unidirectional canine mixed lymphocyte culture (MLC) have shown that, in contrast to the marked inhibition of cellular reactivity of recipient circulating responding lymphocytes against donor stimulating lymphocytes seen with unmodified first-set renal allograft rejection, this inhibition was not seen after second-set transplants. Reactivity of lymph node lymphocytes was augmented after first- or second-set transplants. In addition, serial donor skin allograft and concurrent lymphocyte immunizations resulted in decreasing amounts of inhibition, of recipient circulating MLC-reactive cells as serum antibody levels increased and as the white graft phenomenon occurred in hyperimmunized animals. After second-set renal allograft rejection, and in a highly immunized group undergoing hyperacute renal allograft rejection, there occurred a cytophilic MLC inhibitory factor shown to be IgG. Its association with circulating granulocytes and monocytes and specific inhibition of MLC reactivity against donor lymphocytes was demonstrated. This cytophilic factor should be looked for in future experiments using immunized recipients before concluding whether or not there is inhibition of cellular reactivity in culture.