The role of IL-5, IL-6 and IL-10 in primary and vaccine-primed immune responses to infection with Friend retrovirus (Murine leukaemia virus)

The defence of a host against viral infections is strongly influenced by cytokines, We investigated the role of the B-cell stimulating cytokines IL-5 and IL-6, and the immune-suppressive cytokine IL-10, during primary and secondary immune responses in mice against infection with Friend retrovirus (FV) (Murine leukaemia virus). IL-5(-/-) mice were comparable to C57BL/6 wild-type mice in their ability to control acute FV infection. In contrast, IL-6(-/-) and IL-10(-/-) mice showed significantly enhanced virus loads in spleen cells. However, this impaired control of acute FV replication did not alter the long-term control over persistent FV in IL-6(-/-) and IL-10(-/-) mice. Immunization with a live attenuated vaccine virus prior to challenge protected all three types of cytokine-deficient mice from high levels of spleen virus, despite the finding that the vaccinated IL-5- and IL-6-deficient mice had significantly reduced titres of virus-neutralizing IgG class antibodies. The results indicate that IL-6 and IL-10 contribute to primary immune responses against FV, but are dispensable during persistent infection and vaccine-primed secondary responses.