A lymphocyte proliferation assay was used to examine the helper T cell response to rotavirus in mice following parenteral immunization with the UK strain of bovine rotavirus. Mixed populations of lymphocytes prepared from spleen or peripheral lymph nodes were tested for proliferation in the presence of UK strain rotaviruses, prepared as cell culture lysates, ultracentrifuged (pelleted) lysates, sucrose-purified virus and caesium chloride-purified virus. Live rotavirus induced non-specific

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... ation of lymphocytes, which was not observed in response to inactivated virus. Putative helper T cells of the L3T4+ phenotype were prepared as an enriched population from UK strain-immunized mice or grown in vitro as a polyclonal T cell line. The response of L3T4 +-enriched cells from mice immunized with inactivated virus was dependent on antigen-presenting cells (APCs). Cells obtained following immunization with live virus did not require further addition of APCs. The response of the L3T4 + T cell line was wholly dependent on APCs. UK strain-specific L3T4 + cells responded to whole UK rotavirus and to isolated VP6 of both UK and C486 rotavirus strains. The results indicate that virus-specific L3T4 + T cells are induced following rotavirus immunization and can respond to epitopes on VP6. UK strainprimed L3T4 + cells also responded to an avian rotavirus strain, Ch2, which shares only minimal serological cross-reactivity with the UK strain. T cell recognition of rotavirus may thus be broadly cross-reactive.