Mouse adenovirus K87(MAV) replicate within the intestinal tract of ordinary mice, becoming completely undetectable in feces 3 weeks after infection due to the action of localized neutralizing IgA class antibodies in the intestinal tract. In congenitally athymic nude mice, detection of virus from feces continues up to about 6 weeks after infection, far later than in normal mice. The resistance manifested as disappearance of detectable virus is temporary, and implications of interferon, natural killer cell activation, and macrophage involvement are negative, although cyclophosphamide administration has been demonstrated to eliminate the resistance altogether. Neutralizing anti-bodies are not produced in MAV infected severe combined immunodeficiency (SCID) mice, lacking functional T and B cells, and some mice exhibit definite sustained infections, while others undergo repeated periods of viral replication and resistance, similar to the course of infection in nude mice. And presently, studies are underway to test the assumption that the factor upholding the resistance to virus exhibited by some of the SCID mice is akin to that found in nude mice.