Abstract

The cattle lungworm, Dictyocaulus viviparus, is a parasitic nematode, which can cause severe pulmonary disease. Repeated natural infections result in protective immunity, and a live attenuated vaccine exists. However, live vaccines have several disadvantages, and alternative control methods are needed. Awareness of increasing anthelmintic resistance makes parasite control with reduced reliance on chemotherapeutics preferable, and an effective modern vaccine to D. viviparus based on recombinant antigens would provide a valuable alternative. To enable the design of such a vaccine, identification of the immune mechanisms behind resistance to D. viviparus is fundamental. The overall aim of this thesis was to study cellular immune responses to D. viviparus. In order to identify cells involved in development of protective immunity, mononuclear cell populations in the lungs of experimentally infected calves were studied during two subsequent infections. A large influx of activated γδ T cells was observed in the lungs both after primary infection and reinfection, which suggests a role for γδ T cells in the immune response to D. viviparus. In vitro analyses of lymphocyte responses to D. viviparus revealed that cells from naïve animals were induced to proliferate. Cells expressing CD4, CD8 as well as γδ TCR responded, suggesting that the worms contain substances with a broad mitogenic effect. When investigating responses of cells collected from immune animals, no clear acquired responses were detected. Investigations into the nature of the mitogenic components in D. viviparus indicated that they are low molecular mass immunogenic proteins with so far unknown identities.