Inhibition of graft rejection by LPS: further evidence for effects on T lymphocytes.

The effects of bacterial lipopolysaccharides (LPS) on the growth of allografted lymphoma cells in Balb/c mice were studied. It was determined that the injection of LPS at the time of graft implantation resulted in a transient proliferation and a delay in the rejection of the graft. This effect was not attributable to any enhancement of proliferation of the lymphoma cells by LPS nor to any activity of LPS as a competing antigen or as a polyclonal activator of antibody formation. The in vitro cytotoxicity of peritoneal macrophages from LPS-treated animals against allogeneic lymphoma cells was equal to that of mice not treated with LPS. In vitro proliferation responses of splenic lymphocytes from LPS-treated animals indicated that LPS treatment produced a differential depression of Concanavalin A (Con A) responses but phytohemagglutinin (PHA)-induced responses were elevated significantly. These results suggest that the LPS-induced impairment of cell-mediated immunity involves a subset of Con A reactive T cells whose function is important in allograft rejection.