Stimulatory effect of vitamin A on tumoricidal activity of rat alveolar macrophages

F344 rats were given saline, vitamin A placebo or vitamin A analogues orally for 4 consecutive days. The following day they were killed and their alveolar macrophages (AM phi) were harvested by lavage. The functional integrity of the AM phi was determined by their capacity to phagocytize opsonized SRBC and to kill syngeneic adenocarcinoma cell lines nonspecifically. Results showed that 4 days treatment with greater than 100 IU of vitamin A as retinyl palmitate per gram body weight rendered the AM phi tumoricidal against syngeneic mammary adenocarcinoma cell lines (MADB-100 and MADB-200) and that AM phi activated with retinyl palmitate showed increased ability to phagocytize opsonized SRBC. Other retinoids, such as retinoic acid and retinol, had the same effect of inducing tumoricidal activity in rat AM phi. AM phi harvested from normal rats were also rendered tumoricidal by direct interaction with greater than 10(3) IU ml-1 of retinyl palmitate for 24 h in vitro. Thus, vitamin A at high doses can increase the phagocytic and tumoricidal activities of rat AM phi.