Pathology of Listeria infection in murine severe combined immunodeficiency. A study by immunohistochemistry and electron microscopy.

: Mice bearing the scid mutation lack functional T and B lymphocytes and partially resist infection with the intracellular pathogen Listeria monocytogenes. In this study, we describe the histopathologic features of the infection in scid mice. Infected scid showed hyperplasia of mononuclear cells in lymphoid organs without any evidence of granulomas nor of lymphoid cell development. Mononuclear phagocytes in various tissues of infected scid mice had markedly enhanced expression of class II histocompatibility molecules (or Ia molecules). Furthermore, Ia expression was also found in endothelial and epithelial cells of many organs in the later stages of infection. These results confirm that scid mice have a mechanism for activation of Ia antigen expression, which is independent of lymphocyte function.