Coronin is involved in uptake of Mycobacterium bovis BCG in human macrophages but not in phagosome maintenance

By applying density gradient electrophoresis (DGE) to human macrophages inf ected with Mycobacterium bovis BCG, we were able to separate three differen t bacterial fractions representing arrested phagosomes, phagolysosomes and mycobacterial clumps. After further purification of the phagosomal populati on, we found that isolated phagosomes containing live BCG were arrested in maturation as they exhibited only low amounts of the lysosomal glycoprotein LAMP-1 and processing of the lysosomal hydrolase cathepsin D was blocked. In addition, low amounts of MHC class I and class II molecules and the abse nce of HLA-DM suggest sequestration of mycobacterial phagosomes from anti g en-processing pathways. We further investigated the involvement of the acti n-binding protein coronin in intracellular survival of mycobacteria and sho wed that human coronin, as well as F-actin, were associated with early stag es of mycobacterial phagocytosis but not with phagosome maintenance. Theref ore, we conclude that the unique DGE migration pattern of arrested phagosom es is not as a result of retention of coronin, but that there are other pro teins or lipids responsible for the block in maturation in human macrophage s,