Search

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.

B-cell responses of 3 immunoglobulin isotypes (IgA, IgG, and IgM) were investigated in the large intestine and mesenteric lymph nodes (MLN) of naive or immune mice after inoculation of oocysts of Eimeria falciformis. Primary and anamnestic IgA and IgG lymphocyte responses to E. falciformis occurred in the large intestine of nonimmune and immune mice, respectively. IgA-containing lymphocytes (IgAc) were the largest population of responding B cells in the large intestine. In infected mice, IgAc accumulated in the apical portion of the lamina propria, whereas IgG-containing lymphocytes (IgGc) were more numerous at the base of the lamina propria. No significant increase in the number of IgM-containing lymphocytes (IgMc) was observed in the lamina propria of the large intestine. Primary but no anamnestic B-cell responses occurred in the MLN, and immune mice actually had reduced numbers of IgAc and IgGc in the MLN when compared with naive mice. IgGc were the largest population of responding B cells in the MLN. Thus, IgAc appear to accumulate preferentially at the site of parasite development, whereas IgGc are primarily localized deeper in the lamina propria of the large intestine and in the draining lymph nodes of mice infected with E. falciformis.