M. leprae phagocytosis and its association with membrane changes in macrophages from leprosy patients

Abnormal phagocytosis of Mycobacterium leprae by macrophages of lepromatous patients was demonstrated under various conditions. The largest proportion of macrophages with an excessive bacterial load belonged to the lepromatous group of patients. Lepromatous macrophages treated with Cytochalasin B, an inhibitor of phagocytosis, exhibited a significantly lower degree of ingestion of heat-killed organisms whereas uptake of 'viable' organisms was not affected to the same extent. Regulation of phagocytosis was studied by noting the rate of phagocytosis of M. leprae after the ingestion of a primary particle viz carbonyl iron. Solely in lepromatous macrophages, phagocytosis of carbonyl iron did not result in a decreased uptake of M. leprae implying aberrant phagocytic activity. Lastly, excessive phagocytosis was always noted in macrophages of familial contacts of leprosy patients who displayed decreased Fc receptor expression after M. leprae ingestion. This is of interest since phagocytosis, like Fc receptor expression, is a membrane dependent event and other membrane associated defects have been recognized by us earlier in lepromatous macrophages.