Differences in resistance of C57BL/6 and C57BL/10 mice to infection by Mycobacterium avium are independent of gamma interferon

Abstract

After infection with a low-virulence strain of Mycobacterium avium, C57BL/6 and C57BL/10 mice had clear differences in the control of the infection in their livers and spleens. This difference in susceptibility was not associated with differences in the H-2 complex. It was dependent on the activity of CD4(+) T cells but unrelated to the ability of these cells to secrete gamma interferon or to the development of delayed-type hypersensitivity responses at 3 weeks of infection. It was associated with lower total numbers of CD4(+) cells present in infected spleens and was related to an earlier induction of protective T cells, as measured by adoptive-transfer assays. These data further strengthen the notion of gamma-interferon-independent mechanisms of protection against mycobacteria.

FIG. 1

Proliferation of M. avium 2447 SmT in the organs of mice infected intravenously with 10⁶ CFU. (A) M. avium growth was studied in the livers and spleens of C57BL/6 (□) and C57BL/10 (○) mice for up to 3 months. (B) The growth of M. avium was studied after 4 weeks of infection in C57BL/6, C57BL/10, and B10.D2 mice. Statistically significant differences are labeled (∗∗, P < 0.01) as determined by the Student's t test. Each group consisted of four or five mice.

FIG. 2

Numbers of CD4⁺, CD8⁺, and γδ-TCR⁺ T cells in the spleens of C57BL/6 (open columns) or C57BL/10 (solid columns) mice infected for 4 weeks with M. avium. Statistically significant differences between the two strains are labeled (∗, P < 0.05; as determined by the Student's t test). Cells from individual mice were analyzed, and four mice per group were used.

FIG. 3

(A) Proliferation of M. avium 2447 SmT in the liver of C57BL/6 (squares) and C57BL/10 (circles) mice. Animals were either left untreated before or during infection (Controls) or thymectomized and given anti-CD4 monoclonal antibodies as described in Materials and Methods (CD4-depleted). Statistically significant differences are labeled “∗∗” for P < 0.01 as determined by the Student's t test. (B) In vitro secretion of IFN-γ by spleen cells from the same control animals after stimulation with M. avium CFP antigen (solid symbols) or concanavalin A (open symbols). Triangles represent data from nonstimulated cultures. There were no statistically significant differences in IFN-γ secretion between the two groups of mice as determined by the Student's t test. Four mice per group were examined.

FIG. 4

DTH responses at 3 weeks of infection in C57BL/6 (□) and C57BL/10 (○) mice. Footpad swelling was measured at different time points after injection of either 10 μg of M. avium CFP antigen or PBS. Data are shown as the means of the difference between the swellings in the footpad injected with antigen and in the contralateral one, injected with PBS alone, ± one standard deviation. Differences between the two strains were not statistically significant as determined by the Student's t test.

FIG. 5

Protective efficacy of T-cell-enriched spleen cell suspensions from C57BL/6 (open columns) or C57BL/10 (solid columns) mice infected for 2 or 4 weeks with M. avium compared to cells isolated from untreated animals. Recipient mice were sublethally irradiated C57BL/6 mice. Mycobacterial loads in the recipient animals were evaluated 32 days after infection and spleen cell transfusion. Data are shown as log₁₀ decrease in CFU (protection), calculated by subtracting the geometric mean in the immune groups from that of the nonimmune controls. Statistically significant protection (recipients of immune cells were compared to those receiving nonimmune cells) is labeled “∗” for P < 0.05 or “∗∗” for P < 0.01 (according to the ANOVA test).