Action of histamine and antihistamine on the ingestion of murine leprosy bacilli by macrophages of the rat and the guinea-pig.

The discovery of synthetic antihistaminic substances has had a great influence on studies of the cellular defense mechanism. Experiments with antihistamines have permitted better understanding of the functioning of certain defence processes. These substances inhibit the formation of the first barrier against bacterial invaders, and also the phagocytic activity of fixed (8,9, 10) and mobile (4, 10, 11) cells of the reticuloendothelial system. They also inhibit the action of certain mediators which maintain important functions of the defence apparatus (12,13). Consequently, they aggravate acute and chronic bacterial infections (3,5,6). We have found (3) that synthetic antihistamines also have a deteriorating effect in experimental tuberculosis in guinea-pigs and mice. Later, we showed that a synthetic antihistamine (mepyramine maleate) had a restraining effect on the phagocytosis of tubercle bacilli by monocytes (10) ; and that, contrarily, histamine stimulated the monocytes to an increased phagocytic activity toward the same bacilli (4). We then turned our attention to murine leprosy, another disease in which the mononuclear -macrophages play an important role. The purpose of the present investigation was to ascertain whether a similar mechanism could be detected in the macrophage-parasite relationship in murine leprosy. The first observation was contrary to that which was found with tubercle bacilli: the antihistamine did not inhibit the phagocytosis of Mycobacterium leprae murium by monocytes of guinea-pigs. This negative result stimulated the experiments which are reported here, designed to determine the influence of histamine and antihistamine on the phagocytosis of BCG and M. leprae murium by the monocytes of guinea-pigs and Wiersing rats.