Mycobacterium avium-complex infections in normal and immunodeficient mice.

Specific pathogen-free C57Bl/6 X DBA/2 (B6D2) F1 hybrid mice were challenged aerogenically with M. avium, M. intracellulare and M. scrofulaceum and the resulting lung and spleen infections were followed over a period of several months. Growth of the mouse virulent M. avium 724 and M. intracellulare D673 was more extensive in the susceptible (Balb/c or C57Bl/6) mice than it was in the resistant A/J and B6D2 strains. Oral challenge of normal C57Bl/6 mice with virulent M. avium-complex serotypes resulted in substantial infection of the gut-associated lymphoid tissues, the lungs and spleen. No infection developed when the mice were infected orally with the avirulent MAC serotypes. T-cell depleted Balb/c (nude or Thxb) mice infected with virulent M. avium developed markedly enhanced lung and spleen infections compared to those seen in the immunocompetent controls. T-cell depletion did not potentiate the systemic growth of the avirulent MAC strains. The significance of these growth patterns (especially in the T-cell depleted mouse) is discussed in relation to the development of life-threatening M. avium-complex infections in patients with Acquired Immune Deficiency Syndrome.