Activation of primary lymphocytes requires prolonged lectin stimulation.

T lymphocytes are activated by a complex series of events, but the mechanisms remain unclear. One uncertainty is the time of receptor-ligand interaction necessary for commitment to DNA synthesis and proliferation. Although this issue has broad implications for the interpretation of T cell activation data, it remains unresolved. Therefore, we examined the temporal activation requirements of rat splenocytes stimulated with concanavalin A (Con A) by measuring proliferation, as well as interleukin-2 (IL-2) production and IL-2 receptor IL-2R) expression. Splenocytes stimulated with various Con A concentrations for 3 h did not incorporate significantly more [3H]thymidine than unstimulated splenocytes. Some increase occurred after 6 h of lectin exposure but maximum proliferation occurred only after the 52-h stimulation. Furthermore, Con A incubations of 6 h or more were required for significant increases in IL-2 or IL-2R. Maximum lymphokine production and receptor expression were observed after the 52-h stimulation. Thus, activation of some primary lymphocytes required only 6 h of stimulation, but much longer mitogen contact was necessary for maximum recruitment.