Clonal Expansions of CD8(+) T Cells with IL-10 Secreting Capacity Occur during Chronic Mycobacterium tuberculosis Infection

Cyktor, Joshua C.; Carruthers, Bridget; Beamer, Gillian L.; Turner, Joanne

Following aerogenic infection of CBA/J and C57BL/6 mice with Mtb we observed a gradual accumulation of CD4 + T cells in the lungs of C57BL/6 mice and significantly fewer CD4 + T cells within the lungs of CBA/J mice (Fig. 1a) , as we have previously described [3, 4] . In contrast to the reduced number of CD4 + T cells, CBA/J mice demonstrated a significant late accumulation of CD8 + T cells within the lungs as Mtb infection progressed (Fig. 1b) , eventually reaching or surpassing the number of pulmonary CD8 + T cells observed in C57BL/6 mice. This late accumulation was absent from C57BL/6 mice which reached a plateau at day 60. Skewing of T cell subset proportions in CBA/J mice could be better appreciated by determination of CD4:CD8 ratios throughout the course of infection (Fig. 1c) , where a significant decline in the ratio of CD4 + to CD8 + T cells was observed by day 90 of Mtb infection, preceding the increasing CFU within the lungs of CBA/J mice (Fig. 1d) [4, 6] . BrdU staining of pulmonary CD4 + (Fig. 1e) and CD8 + T (Fig. 1f) cells from CBA/J mice was not dramatically altered throughout infection, suggesting that the increased numbers of CD8 + T cells that were evident in CBA/J mice may not be due to local proliferation, but a consequence of enhanced cellular recruitment. CBA/J mice are known to produce abundant IL-10 in their lungs as Mtb infection progresses [5] and IL-10 can stimulate the proliferation of CD8 + T cells [41] . Therefore, we examined the numbers of CD4 + and CD8 + T cells present in the lungs of CBA/J IL-10 2/2 mice over the course of Mtb infection (Fig. 1g, h) and did not observe any differences between wild-type and IL-10 2/2 CBA/J mice in CD8 + T cell accumulations at late stages of infection, demonstrating that CD8 + T cell expansions occur independent of IL-10. A significant increase in CD4 + and CD8 + T cells was observed in CBA/J IL-10 2/2 mice at day 30, reflecting enhanced T H 1 immunity in these mice (unpublished observations). These data demonstrate that the accumulation of CD8 + T cells in the lungs of CBA/J mice during chronic infection is not mediated by IL-10.