An immunosuppressive murine leukaemia virus induces a Th1 → Th2 switch and abrogates the IgM antibody response to sheep erythrocytes by suppressing the production of IL-2

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Abstract
SUMMARY: Many retroviruses have tropism for cells in the immune system and have a propensity to induce immunosuppression in the host. Some of the effects of retroviruses on immune cell function are thought to be mediated through cytokines. Friend ImmunoSuppressive virus-2 (FlS-2) is a low oneogenic murine leukaemia virus (MuLV) that induces lymphadenopathy and immunosuppression in NMRI mice. The role of T cell cytokines during the generation of a primary antibody response in healthy and FIS-2-infected mice was studied following the antibody response to sheep erythrocytes by an in vitro immunization (IVI) technique. In cultures from FIS-2-infected mice, the antibody response was reduced compared with cultures from uninfected mice and the production of the Th2 cytokines IL-4 and IL-6 was elevated, whereas the Th1 cytokines IL-2, interferongamma (IFN-γ) and tumour necrosis factor-alpha (TNF-α) were reduced. The suppressed antisheep erythrocyte antibody response in cultures from mice infected with FIS-2 seemed to be caused by an insufficient production of IL-2, since addition of recombinant IL-2, stimulated the antibody response. This effect was also observed in cultures depleted of T cells, indicating a direct effect of IL-2 on B cells. A switch to a Th2 cell response and suppression of IL-2 production might play a central role in the immune cell dysfunction induced by FIS-2.