Retinoids as regulators of macrophage function.

Retinol (vitamin A) and retinoic acid, at concentrations in the physiological range, were found to exert potent regulatory effects on the function of macrophages; suppressing the expression of Fc receptors and the subsequent phagocytosis of opsonized cells but enhancing production of the tumouricidal enzyme arginase. Another dietary essential lipid-soluble molecule, arachidonic acid, from which a number of active molecules known to regulate cellular function are derived, had no effect on macrophage receptor expression or phagocytosis.