Mycobacterium avium infection in BALB c and SCID mice

BALB/c and severe combined immunodeficient (SCID) mice were inoculated intr aperitoneally with Mycobacterium avium and the numbers of cfu were monitore d for 70 days in spleen, liver, lung, kidney brain and peritoneum. While BA LB/c mice formed typical granulomas and controlled bacterial growth in orga ns, a delay in development of lesions and a modest containment of infection were observed in SCID mice. In the spleen of BALB/c mice, in which bacteri al growth was contained, macrophages (M phi) and natural killer (NK) cell n umbers increased greater than or equal to 4.2 times and T- and B-cell numbe rs increased greater than or equal to 1.8 times after 42 days of infection; conversely, a low recruitment of mononuclear cells was observed in the spl een of SCID mice, where M. avinm proliferated efficiently. Unlike visceral organs, a pronounced decrease in the number of cfu was observed in the peri toneum of BALB/c mice, concomitantly with a greater than or equal to 31.7-f old increase in MB and NK cells and a greater than or equal to 9.1-fold inc rease in T and B cells. In the peritoneum of SCID mice only a bacteriostati c effect was observed despite a greater than or equal to 56.7-fold increase in Mo and NK cells and a greater than or equal to 22.3-fold increase in T and B cells. These results suggest that while an intact immune response can efficiently control M avium infection in the spleen and peritoneum of BALB /c mice, cells of the innate immune system such as Mo and NK cells play a r ole in the containment of bacterial growth in the peritoneum, but not splee n, of SCID mice.