Mitomycin C-treated or irradiated concanavalin A-activated T cells augment the activation of cytotoxic T cells in vivo

IL-4-based helper activity of CD4+ T cells is radiation sensitive

The capacity of CD4+ T cells to induce IgG synthesis in B cells has been known to be radioresistant for more than 20 years. However, the radiation sensitivity of helper T cells with regard to their ability to induce the synthesis of isotypes other than IgG has not been studied. We therefore irradiated KLH-primed lymph node T cells and examined their capacity to induce IgG, IgM, and IgE synthesis in hapten-primed B cells. We demonstrated that while the capacity of KLH-primed lymph node cells to induce IgG synthesis was not affected by irradiation, the capacity of such T cells to induce IgE synthesis was greatly reduced by gamma-irradiation. This was consistent with our observations that IL-4 and IL-5 synthesis in such cells was greatly diminished by irradiation, whereas IL-2 synthesis was only minimally affected. A similar differential sensitivity to irradiation of the helper activity of Th1 and Th2 clones was observed with regard to their ability to induce IgE and IgG synthesis under cognate conditions. Irradiation greatly inhibited the capacity of Th2 clones to induce IgE synthesis, but only minimally affected the capacity of Th1 clones to induce IgG synthesis in primed B cells. The capacity of irradiated Th2 clones to induce IgE synthesis was restored by the addition of IL-4 and IL-5. These results taken together indicated that the sensitivity to irradiation of T helper cells with regard to the induction of IgE but not IgG synthesis was due to the sensitivity to irradiation of the production of IL-4 but not of IL-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Abrogation of staphylococcal enterotoxin A-induced suppressor cell activity by the anti-Tac monoclonal antibody

Human mononuclear cells stimulated with staphylococcal enterotoxin A (SEA) for 2-6 days significantly suppress [3H]thymidine incorporation and reduce the levels of interleukin 2 (IL-2) and interferon (IFN) in culture medium when added to fresh, polyclonally activated mononuclear cells. The inhibitory capacity of the cells correlates well with the expression of IL-2 receptors. Lymphocytes obtained 3 days after stimulation with SEA, when the IL-2 receptor expression is high, are more potent inhibitors than cells obtained 2, 6, 11 or 14 days after stimulation, when the IL-2 receptors are less expressed on lymphocytes. T4+ and T8+ cells were both found to be inhibitory. Irradiation of the cells with 15 Gy before stimulation with SEA reduced but did not eliminate their suppressive capacity. The expression of the IL-2 receptor was lower in the irradiated cells. Irradiation or mitomycin-C treatment of cells after 3 and 5 days of SEA exposure had no effect on their inhibitory capacities. Pretreatment of the cells with IL-2 could partially reverse their suppressive effect on recorded IL-2 levels of stimulated fresh cultures. A complete reversal was obtained with the anti-Tac monoclonal antibody, which binds to the IL-2 receptor. The collective data show that the SEA-induced suppression of IL-2 activity in lymphocyte culture medium is not due to a suppression of the IL-2 production but rather depends on depletion of IL-2 due to absorption of IL-2 from the culture medium.

Histamine inhibits interferon-gamma production via suppression of interleukin 2 synthesis

Histamine, a modulator of various immune functions, inhibits the production of interleukin 2 (IL-2) and interferon-gamma (IFN-gamma) by polyclonally activated human blood mononuclear cells. The histamine-induced inhibition of IFN-gamma synthesis can be completely eliminated by the addition of recombinant IL-2. The IFN-gamma synthesis by T8+ lymphocytes is highly dependent on IL-2 supplied either by the IL-2 producing T4+ lymphocytes or through exogenous addition of recombinant IL-2. It is concluded that histamine acts primarily on the interleukin 2 synthesis by the T4+ lymphocytes and as a consequence of this inhibition, interferon-gamma production is reduced.