Effect of Mycobacterium leprae-infected Schwann cells and their supernatant on lymphocyte neuroglia interaction.

Since the resolution of neural lesions and subsequent nerve damage in leprosy must inevitably involve the participation of immune cells sensitized to Mycobacteria, we have used the dissociated Schwann cell culture model to study the relationship between M. leprae-infected Schwann cells and sensitized immune cells. Our earlier study on light and ultrastructural observations showed that on infection with M. leprae, the cytomorphology of Schwann cells remains unaffected, while degenerative changes suggestive of apoptosis are seen in extraneous lymphocytes which are subsequently phagocytosed by the Schwann cells. We now present additional evidence confirming that the phagocytosis of splenic cells by Schwann cells is indeed a two-step process. The first involves M. leprae-dependent cytotoxicity to splenic cells. This is followed by phagocytosis of these cells, which is a secondary and M. leprae-independent phenomenon. This finding has implications particularly on the weak inflammatory response observed in nerve lesions of a majority of lepromatous patients.