Differences in engulfing ability and phagolysosome formation between mononuclear-macrophages and neutrophils during Leptospira interrogans infection / 中华微生物学和免疫学杂志

Objective To understand the differences in engulfing ability and phagolysosome for-mation between mononuclear-macrophages and neutrophils during Leptospira interrogans infection. Methods Human THP-1 monocytes and HL-60 cells were pretreated with PMA ( phorbol-12-myristate-13-acetate) and ATRA ( all-trans retinoic acid) to differentiate them into mononuclear-macrophages and neutrophils, respec-tively. The phagocytosis of Leptospira interrogans in THP-1-PMA mononuclear-macrophages and HL-60-AT-RA neutrophils was detected by confocal microscopy. The morphology of intracellular Leptospira was deter-mined by transmission electron microscopy. The viability of phagocytized Leptospira and the percentages of dead Leptospira were analyzed by confocal microscopy and spectrofluorimetry, respectively. Confocal micros-copy was used to measure the formation of phagolysosomes in different phagocytes. Results Both THP-1-PMA mononuclear-macrophages and HL-60-ATRA neutrophils could phagocytize Leptospira interrogans, but the phagocytic ability of the former was notably stronger than that of the latter (P<0. 05). Intracellular Lep-tospira were surrounded by phagocytic vesicles in both types of phagocytes. THP-1-PMA mononuclear-mac-rophages were better than HL-60-ATRA neutrophils in killing intracellular Leptospira (P<0. 05). More phagolysosomes were formed in THP-1-PMA mononuclear-macrophages than in HL-60-ATRA neutrophils ( P<0. 05). Conclusions Human mononuclear-macrophages but not neutrophils act as major phagocytes that play an important role in phagocytizing and killing Leptospira during infection. Less fusion of the phagosomes with lysosomes may be responsible for the lower Leptospira-killing ability of neutrophils.

Modulation of phagolysosome maturation by bacterial tlyA gene product.

The pathogenic traits of TlyA proteins of Mycobacterium tuberculosis are not known. Expressions of TlyA in bacteria that do not express endogenous TlyA adhere better to RAW264.7 macrophages and get phagocytosed efficiently. The internalized bacteria avoid acidification to the extent of >65% in the case of both TlyA-expressing E. coli and M. smegmatis. Consistent with this observation, we have observed decreased co-localizaton of Lysosomal Membrane Associated Protein-1 (~35%), Early Endosomal Antigen-1 (~34%), Rab5 (~30%) and Rab7 (~35%) and enhanced colocalizaton of Rab14 (~80%) on both TlyA-expressing bacteria as well as on TlyA-coated latex beads. These results suggest that the mycobacterial TlyA, in general, can modulate phagolysosome maturation pathway immediately after entry into macrophages, while other important molecules may aid the bacterium for long-term, intracellular survival at later point of time.