FUSION OF AZUROPHIL GRANULES WITH PHAGOSOMES AND ACTIVATION OF THE TYROSINE KINASE HCK ARE SPECIFICALLY INHIBITED DURING PHAGOCYTOSIS OF MYCOBACTERIA BY HUMAN NEUTROPHILS

Pathogenic mycobacteria parasitize macrophages and reside within phago somes, which do not fuse with lysosomal granules. Mycobacteria are als o internalized by nentrophils, which possess at least two types of gra nules, specific and azurophil granules, the latter being specialized l ysosomes, Here, we investigated the ability of mycobacteria to inhibit the fusion of these granules with their phagosomes in human neutrophi ls. It was found that when pathogenic (Mycobacterium kansasii and Myco bacterium avium) or nonpathogenic (Mycobacterium smegmatis and Mycobac terium phlei) mycobacteria were internalized by neutrophils, they indu ced the inhibition of azurophil granule fusion with phagosomes even wh en they were serum opsonized, In contrast, secretion of specific granu le content and production of O-2(-) both of which contribute to the ne utrophil bactericidal response, were triggered, Hck is a Src family ty rosine kinase associated with azurophil granules. During internalizati on of zymosan, azurophil granules fused with phagosomes and Hck was ac tivated and translocated to the phagosomal membrane, whereas in neutro phils engulfing mycobacteria, Hck did not translocate and remained una ctivated, The activation of the tyrosine kinase Fgr was not affected. These results indicate that 1) pathogenic and nonpathogenic mycobacter ia trigger similar bactericidal responses in neutrophils, 2) phagocyto sis and fusion of azurophil granules can be uncoupled by mycobacteria, and 3) Hck could be one of the key elements of the azurophil secretor y pathway that are altered during phagocytosis of mycobacteria.