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 cy tokines, 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 sec ondary immune responses in mice against infection with Friend retrovirus (F V) (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 spl een cells. However, this impaired control of acute FV replication did not a lter the long-term control over persistent FV in IL-6(-/-) and IL-10(-/-) m ice. Immunization with a live attenuated vaccine virus prior to challenge p rotected all three types of cytokine-deficient mice from high levels of spl een virus, despite the finding that the vaccinated IL-5- and IL-6-deficient mice had significantly reduced titres of virus-neutralizing IgG class anti bodies. The results indicate that IL-6 and IL-10 contribute to primary immu ne responses against FV, but are dispensable during persistent infection an d vaccine-primed secondary responses.