ROLES OF CALCIUM AND ANNEXINS IN PHAGOCYTOSIS AND ELIMINATION OF AN ATTENUATED STRAIN OF MYCOBACTERIUM-TUBERCULOSIS IN HUMAN NEUTROPHILS

The phagocytic function of neutrophils is a crucial element in the hos t defence against invading microorganisms. We investigated phagocytosi s and intracellular killing of an attenuated strain of Mycobacterium t uberculosis (H37Ra) by human neutrophils focusing on the role of the c ytosolic free calcium concentration [Ca2+](i) and certain cytosolic ca lcium-dependent membrane-binding proteins annexins. Phagocytic uptake did not trigger a calcium rise and occurred independently of different calcium conditions, and in a serum-dependent manner. Changes in the v iability of H37Ra were determined by agar plate colony count and a rad iometric assay. Neutrophils showed a capacity to kill ingested mycobac teria and this occurred without a rise in [Ca2+](i). The ability to ki ll H37Ra decreased in the absence of extracellular calcium and when in tra-extracellular calcium was reduced. Immunofluorescence staining rev ealed that during phagocytosis of H37Ra, annexins III, IV and VI trans located from cytoplasm to the proximity of the H37Ra-containing phagos omes; whereas the localization of annexin I and V remained unchanged. The translocation of annexin IV occurred even when Ca2+-depleted neutr ophils ingested H37Ra in the absence of extracellular calcium. We conc luded that neutrophil-mediated killing of mycobacteria is a Ca2+-depen dent process. The fact that the association of certain annexins to the membrane vesicle containing H37Ra differ from other phagosomes sugges ts a selective regulatory mechanism during phagocytosis of mycobacteri a by neutrophils. (C) 1998 Academic Press Limited.