Restrained cytosolic localization of M. leprae in human skin biopsy specimens. Leprosy patient skin biopsy specimens were analyzed using TEM. Immunogold labeling for cathepsin D was used to label lysosomes and phagolysosomes. (A) TEM image of a patient skin biopsy specimen with cytosolic M. leprae. The mycobacteria were not enclosed with host membranes. (A′) Schematic representation of panel A. Orange indicates M. leprae, blue lines indicate host membranes, and green indicates mitochondria. (B) M. leprae present in the phagolysosome. The mycobacterium is enclosed by host membranes and immunogold labeled for the lysosomal marker cathepsin D. (B′) Schematic representation of panel B. Black dots indicate cathepsin D labeling, orange indicates M. leprae, and the blue lines indicate phagolysosomal membranes. (C) Quantification of the average percentage of M. leprae bacteria present in the cytosol. The error bar indicates the standard deviation from 4 different patients, and n represents the total number of intracellular bacteria (see also Fig. S2C in the supplemental material).
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