[Modulation of lymphocyte proliferation by serum factors and lipopolysaccharide]

The in vitro proliferative response of rat lymphoctes culitivated in increasing concentrations of calf serm (LCS) was measured by the incorporation of 3H-thymidine. Results showed that in contrast to the response of PHA, the response to concanavlin A (conA) was greatly dependent on the concentration of serum in the medium. Kinetics of the response of ConA indicated that increasing concentrations of LCS unblocked the non-response to supraoptimal doses of the mitogen. The supportive effect of LCS was not due to an increase in cell viability and was abolished when serum was dialyzed. By contrast, lipopolysaccharide (LPS) exerted an adjuvant effect on the response to optimal and suboptimal concentrations of ConA without unblocking the non-response to high doses. LPS facilitated the response to ConA of a distinct subpopulation of T cell isolated by separation on nylon wool columns. This in vitro model allowed us to study some factors which may be implicated in tolerance and immunity.