Possible in vivo modulation of the immune system by the leukotriene, LTB4. I. Delayed suppression of cellular immunity.

Leukotriene B4 (LTB4) is a potent mediator of inflammation. Recently, reports have indicated that LTB4 may affect lymphocyte function in vitro. Therefore, we examined the effect of LTB4 following intrapleural injection to determine if LTB4, released at an inflammatory site, would affect rat mononuclear cell function. LTB4 appeared to have little effect on mitogen-induced lymphocyte transformation nor was any direct mitogenic effect observed at concentrations ranging from 10(-6)-10(-12) molar. However, a marked inhibition of a one-way mixed lymphocyte reaction was observed upon in vitro culturing of lymphocytes from animals examined 72-96 hr after a single intrapleural injection of LTB4. We conclude that LTB4 released at inflammatory sites may play a role in modulating immune function but it appears not to be a direct effect but rather, although the evidence is circumstantial, an indirect effect.