Induction of lymphokine-activated killer activity in rat splenocyte cultures: The importance of 2-mercaptoethanol and indomethacin

The role of 2-mercaptoethanol and indomethacin in the induction of lymphokine-activated killer (LAK) activity by interleukin-2 (IL-2) in rat splenocyte cultures was investigated. Spleens from 4-month-old male rats of five different strains were tested. Splenocytes were cultured for 3-5 days in the presence of IL-2 (1000 U/ml) and LAK activity was assessed by 4-h51Cr release assays with P815 and YAC-1 cells as targets. LAK activity could be induced by IL-2 in splenocytes from all rat strains, but only when 2-mercaptoethanol was present in the culture medium. Optimal LAK activity was induced when the 2-mercaptoethanol concentration in splenocyte cultures was at least 5 μM. Different rat strains showed differences in levels of in vitro induction of LAK activity. In the presence of 2-mercaptoethanol the level of LAK activity induced by IL-2 was high in BN and Lewis rats, intermediate in Wistar and Wag rats, and low in DZB rats. In the absence of 2-mercaptoethanol no or minimal LAK activity was induced. Furthermore we observed that addition of 50 μm indomethacin to the culture medium in the presence of 2-mercaptoethanol augmented the induction of LAK activity to some extent. In the absence of 2-mercaptoethanol, addition of indomethacin resulted only in low levels or no induction of LAK activity. We conclude that for optimal induction of LAK activity by IL-2 in rat splenocyte cultures 2-mercaptoethanol is essential, while indomethacin can only marginally further improve this induction

Mechanism of action of glucocorticosteroids. Inhibition of T cell proliferation and interleukin 2 production by hydrocortisone is reversed by leukotriene B4.

The mechanism whereby glucocorticosteroids are immunosuppressive is unknown. One potential mechanism of action of these compounds is inhibition of arachidonic acid metabolism. We found that the inhibition of lymphocyte proliferation by hydrocortisone or dexamethasone was mimicked by nonspecific lipoxygenase inhibitors and also by a specific 5-lipoxygenase inhibitor, but not by a specific cyclooxygenase inhibitor. Mitogen-stimulated cultures of T cells produce approximately 5 X 10(-9) M leukotriene B4 (LTB4) in 24 h. This production of LTB4 is completely inhibited by concentrations of hydrocortisone or lipoxygenase inhibitors that inhibit mitogen-induced [3H]thymidine incorporation. The inhibition of lymphocyte proliferation by either hydrocortisone or by the 5-lipoxygenase inhibitor was totally reversed by LTB4 but not by leukotriene C4 or leukotriene D4. LTB4 had no effect on the inhibition of lymphocyte proliferation by noncorticosteroids such as prostaglandin E2, histamine, or gamma-interferon. The inhibition of interleukin 2 (IL-2) production by hydrocortisone or dexamethasone was also completely reversed by exogenous LTB4. LTB4 alone did not cause IL-2 production or cell proliferation when added to resting lymphocytes. Thus, endogenous LTB4 production appears to be necessary but not sufficient for phytohemagglutinin-induced IL-2 production and lymphocyte proliferation. Glucocorticosteroids inhibit IL-2 production and lymphocyte proliferation by inhibiting endogenous LTB4 production

Differential inhibition of T cell receptor signal transduction and early activation events by a selective inhibitor of protein-tyrosine kinase.

Abstract Engagement of the TCR (CD3-Ti) by Ag/MHC, CD3 mAb, or lectin mitogen stimulates the very early tyrosine phosphorylation of several cellular substrates including TCR-zeta. The T cell specific protein-tyrosine kinase (PTK), p56lck, has been implicated in the tyrosine phosphorylation of TCR-zeta. However, the significance of this event with regard to CD3-Ti signal transduction remains unclear. Herein, we have investigated the effect of the selective PTK inhibitor genistein (4',5,7-trihydroxyisoflavone) on cellular events associated with activation via CD3-Ti triggering. Genistein inhibited the T cell PTK, p56lck, in a dose-dependent fashion with an ID50 = 40 microM. Genistein also inhibited CD3 mAb or PHA-induced TCR-zeta chain phosphorylation in intact peripheral blood T cells. Genistein blocked the expression of IL-2 and IL-2R (CD25) in T cells stimulated with PHA/PMA or CD3 mAb/PMA, but did not inhibit the de novo expression of the CD69 early activation Ag, which is induced primarily by a PKC-dependent pathway. IL-2 and CD25 expression induced by calcium ionophore A23187 and PMA was largely refractory to inhibition by genistein, suggesting an effect of the drug on calcium-dependent pathways stimulated via CD3-Ti triggering. In this last regard, genistein partially inhibited the CD3 mAb-induced rise in [Ca2+]i but did not inhibit PHA- or CD3 mAb-induced phosphatidylinositol hydrolysis. Consequently, protein-tyrosine phosphorylation does not appear to be a prerequisite for CD3-Ti-mediated activation of phosphatidylinositol-specific phospholipase C activity and PIP2 hydrolysis. An alternative role for PTK in CD3-Ti signal transduction is suggested.</jats:p