Augmentation of human natural cytotoxic cell activity by leukotriene B4 mediated by enhanced effector-target cell binding and increased lytic efficiency.

The addition of leukotriene B4 (LTB4) to cytotoxicity assays measuring natural killer (NK) or natural cytotoxic (NC) cell activities resulted in significantly augmented killing of K562 or herpes simplex virus (HSV)-infected target cells, respectively. Since the mechanism of cytotoxicity implies several steps, including the binding of effectors to targets which is Mg2+-dependent and the programming of lysis of the target which is Ca2+-dependent, we undertook to define the step(s) at which LTB4 acted in augmenting cytotoxicity. Our results showed that LTB4 significantly increased the percentage of effector-target conjugates when K562- or HSV-infected targets were incubated with lymphocytes. Maximal binding occurred at a concentration of LTB4 of 1 X 10(-10) M. Preincubation of lymphocytes and not target cells with LTB4 was sufficient to observe the increased binding. PBML binding to and killing of the NK-resistant target clone I, derived from K562, was not enhanced by LTB4. In the absence of Ca2+, cytotoxicity was impaired and LTB4 could not restore it. Use of a single cell lytic assay demonstrated augmented efficiency of lysis of both K562 and HSV-infected targets in the presence of LTB4. These findings suggest that LTB4 may augment natural cytotoxicity by enhancing target cell recognition by cytotoxic effector cells and subsequently by augmenting their lytic efficiency.