EXPERIMENTAL MURINE LEPROSY .8. ULTRASTRUCTURAL FEATURES OF INFLAMMATORY EXUDATE AND BACTERIAL MORPHOLOGY IN C3H AND C57BL MICE AFTER FOOT-PAD INOCULATION WITH MYCOBACTERIUM-LEPRAEMURIUM

Abstract

Mice of the inbred strains C57BL and C3H were inoculated in the foot-pads with M. lepraemurium (MLM) and the inflammatory reaction was studied using light microscopy and EM. In C57BL mice a granulomatous reaction developed 3-4 wk after inoculation. The inflammatory exudate at this stage showed numerous lymphocytes, monocytes and macrophages. The latter cell type often contained many lysosomes and appeared activated. The bacilli which were all within phagosomes showed extensive electron dense aggregates of the cytoplasm suggesting severe damage. Lymphocytes and macrophages in close contact with each other were often observed. In macrophages containing damaged bacilli, spherical lipid-like bodies surrounded by granular endoplasmic reticulum were observed. This cell product could be of some significance for the bactericidal function of the macrophage. The cellular infiltrate developing in C3H mice showed no lymphocytes and consisted exclusively of macrophages. These were all heavily loaded with bacilli. The vast majority of bacilli encountered in this strain was morphologically intact and presumably viable. Lipid-like bodies similar to those observed in infected C57BL macrophages were not encountered in C3H mice. Unless the infected macrophages become immunologically activated they are apparently unable to cause bacterial damage or to inhibit the growth of MLM.