Immunobiology of germfree mice infected with Nocardia asteroides.

Nocardia asteroides GUH-2 was administered either intranasally or by intravenous inoculation into (i) conventionally grown, (ii) germfree, and (iii) lipopolysaccharide-treated germfree NIH:S mice. The number of bacteria within the lungs, brain, kidneys, adrenals, liver, spleen, and blood was quantitated at 3, 24, 72, and 168 h after infection. Further, the histological changes that occurred in each of these organs after infection were studied. The data demonstrated that germfree mice were significantly more susceptible to the acute phase of infection caused by N. asteroides than the conventionally grown animals. The brains and lungs of these mice were affected most dramatically. Pretreatment of the germfree mice with lipopolysaccharide completely reversed this enhanced susceptibility and rendered the animals more resistant to infection than the conventionally grown mice. These observations establish further the role of macrophage activation and the development of cell-mediated immunity in host resistance to nocardia. In addition, the presence of a resident microflora within the host appears to be important in the development of resistance to systemic nocardial infections.