Early response of mouse foot pads to Mycobacterium laprae

The purpose of these experiments was to study the early response of mouse foot pads to Mycobacterium leprae. To accomplish this, mice were inoculated in both foot pads with large and small numbers of organisms. The animals were sacrificed at intervals from 2 hr to 27 days after inoculation. The microscopical results, which utilized normal BALB/c and thymectomized-irradiated B6C3F(1) mice, showed that the tissue responded first with an influx of polymorphonuclear cells and later lymphocytes and monocytes. The latter formed a diffuse infiltrate in the tissues. Under conditions where growth normally occurred, the mononuclear cell infiltrate did not persist. The organisms were found within phagocytic cells and the interstitial space. They were always contained within a phagosome and often fused with lysosomes. Most of the organisms appeared to be degenerating at all of the times studied. No organisms were observed in striated muscle fibers of tissues studied.