Cellular and humoral factors governing canine mixed lymphocyte cultures after renal transplantation: I. Antibody

The one-way mixed lymphocyte culture (MLC) in unrelated mongrel dogs has been demonstrated to measure both cellular and humoral immunity of unmodified neck kidney allograft rejection. Peripheral blood lymphocytes of five allograft recipients were cultured, together with either lethally X-irradiated donor or indifferent lymphocytes. Either autologous or homologous plasma or inactivated serum was added. In control experiments, stimulating and responding cells from donors, recipients of neck kidney autografts, or normal dogs were combined in MLC, and tritiated thymidine uptake between 15,000 and 30,000 counts/min (CPM) indicated strong responses pre- and postoperatively. By contrast, between 4 and 14 days after allografting there was complete disappearance of recipient lymphocyte reactivity, most specifically against donor lymphocytes, in both autologous and homologous plasma and serum. Tritiated thymidine uptake in these cultures was similar to negative control mixed lymphocytes cultured with X-irradiated autologous lymphocytes (<1,500 CPM). After 14 days, MLC reactivity returned in homologous plasma. However, inhibition persisted in autologous plasma up to 6 months after transplantation. IgG separated on DEAE columns from recipient immune sera specifically caused the inhibition. MLC inhibition correlated with cytotoxicity titers but was a more sensitive detector of antibody. Evidence for the influence of cytotoxic as well as enhancing antibody on the MLC reaction is presented.