The role of CD8+ cells in the establishment and maintenance of a Trichuris muris infection

Chronic infection by the caecal-dwelling intestinal murine nematode Trichuris muris occurs if given as a high-dose infection to 'susceptible' AKR mice or as a low-dose infection to the normally 'resistant' C57BL/6 mouse strain. Both regimes result in a type 1 cytokine response, i.e. high levels of IFN-γ and IL-12. Here we show this susceptible response is associated with a large population of CD8+ IFN-γ+ cells within the mesenteric lymph nodes and numerous CD8+ cells infiltrating the caecal mucosa. Despite this, the in vivo abolition of CD8+ cells within AKR and C57BL/6 mice, either prior to infection or once infection has become established, failed to affect chronicity, implying that CD8+ T cells are not essential for the initiation or maintenance of the susceptible response to T. muris. Interestingly, the percentage of IFN-γ+ CD4+ cells increased in treated groups, perhaps in a compensatory role. The majority of antigen-specific cytokine responses were comparable in both treated and control groups, although IL-5 was fivefold higher in animals receiving anti-CD8 mAbs and IFN-γ was also raised in treated mice. Mastocytosis was unaltered by CD8 depletion, however, paradoxically, eosinophilia within the caecum was reduced in treated mice. Together these data clearly demonstrate that CD8+ T cells are associated with chronic T. muris infection; however, these cells are dispensable for both the early and late phases of this response, but do appear to play a role in the regulation of certain cytokines and caecal eosinophilia.