Effects of retinoids on macrophage function and IL-1 activity

The effects of three retinoids, all-trans-retinoic acid (RA), 13-cis-retinoic acid (cRA), and N-(4-hydroxyphenyl) retinamide (4-HPR), on macrophage function were evaluated. In vitro, RA, cRA, and 4-HPR caused a greater than twofold increase in phagocytosis of IgG-sensitized bovine erythrocytes (IgG-ORBC) by a mouse macrophage cell line (RAW). Significant increases in phagocytosis were produced by retinoid concentrations as low as 2 x 10(-10) M. RA also significantly increased phagocytosis of IgG-sensitized ORBC by BALB/c peritoneal macrophages in vitro. The ability of RAW macrophages to bind IgG-ORBC was significantly increased by 10(-6) to 10(-14) M RA. The potentiation of mitogenic responses of spleen cells to Con A and PWM by RA was relatively independent of macrophage function, i.e., splenocytes that were macrophage-depleted were responsive to the potentiating effects of RA. The effects of retinoids on T-cell-dependent B-cell mitogenesis induced by PWM appeared not to be dependent on their previously reported capacity to alter prostaglandin synthesis. Treatment of spleen cells with 10(-6) M indomethacin did not abolish the potentiating effects of RA. However, RA in a dose-dependent fashion increased IL-1 activity at the level of the target T-cell. The greatest potentiation of IL-1 activity was at 10(-8) M RA. These results show that retinoids can modulate macrophage function at two different levels: potentiation of phagocytosis and potentiation of IL-1 activity at the level of the T-cell.