Lymphocyte activation and cytokine production by Pisum sativum agglutinin (PSA) in vivo and in vitro

Mice spleen cells were incubated in vitro for 24 h with Pisum sativum agglu tinin (PSA). The addition of these supernatants (SN) to macrophage cultures induced the production of nitric oxide (NO) by these cells in a dose-depen dent manner. NO release was blocked in the presence of IFN gamma antibodies and partially inhibited by TNF alpha antibodies. The ability of PSA in ind ucing the production of IFN gamma and TNF alpha by spleen lymphocytes was c onfirmed assaying these cytokine levels in the SN, Spleen cells stimulated in vitro with PSA were highly activated showing an increased expression of the earlier activation marker, CD69, and a great proliferative response. On the other hand, spleen cells obtained from mice treated with PSA 24 h earl ier, did not produce significant levels of IFN gamma or TNF alpha when incu bated in vitro and showed a significantly lower proliferation rate when pul sed in vitro with PSA or Concanavalin A (ConA). The lower responsiveness to mitogens was also evident after 48 and 72 h after the treatment in vivo wi th the lectin, Nevertheless, the flow cytometric analysis of spleen lymphoc ytes obtained from PSA-treared animals showed a high degree of activation i n cells CD3(+), There was a decrease in the expression of L-selectin and VL A-4, when compared to controls, in parallel with a significant increase in the expression of CD69 and CD122 (IL-2R) in lymphocytes recovered from PSA- injected animals. The data point to evidence that PSA induces immunomodulat ory effects, activating spleen lymphocytes in vivo, which become unresponsi ve to a second stimulation in vitro. (C) 1999 Elsevier Science B.V. All rig hts reserved.