DISTRIBUTION OF ANNEXIN-I DURING NON-PATHOGEN OR PATHOGEN PHAGOCYTOSIS BY CONFOCAL IMAGING AND IMMUNOGOLD ELECTRON-MICROSCOPY

Annexin I is an abundant protein in U937 cells differentiated towards a macrophagic phenotype. These cells become able to kill Escherichia c oli, however, the intracellular pathogen Brucella suis, known to inter fere with phagosome maturation, multiply in these differentiated cells . We have analysed by confocal and electron microscopy the cellular lo calization of annexin I during phagocytosis of yeast, non-pathogenic E . coli and the intracellular pathogen B. suis. Using immunocytochemica l detections annexin I was found mainly as patches in the cytoplasm of uninfected cells. Upon phagocytosis of yeast or E. coli organisms, an nexin I rapidly translocated and concentrated around phagosomes. On th e other hand, annexin I was never detected around live B. suis-contain ing phagosomes. However, when dead brucellae were used, annexin I did translocate to the periphagosomal region. Our results suggest that ann exin I could play a role in the molecular mechanism of phagosome matur ation, which is impaired by some intracellular pathogens. (C) 1996 Aca demic Press Limited