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The contribution of humoral immunity to the control of avian reoviral infection in chickens after vaccination with live reovirus vaccine (strain 2177) at an early age

The presence of maternal immunity in broilers does not preclude the successful protective immunization with an attenuated live reovirus vaccine at 1-day-old. This was recently demonstrated in a reovirus challenge model based on reovirus isolation from different organs (van Loon et al., 2002). Discrimination between challenge and vaccine virus was made by specific monoclonal antibody. Notably, at the day of challenge the levels of circulating reovirus-specific antibodies proved to be minimal or undetectable. This suggested an antibody-independent vaccination-induced immunity under the chosen conditions. In the present study we assessed the contribution of specific humoral responses in the same experimental model, by evaluating the control of a virulent challenge infection in the complete absence of B cells as a result of cyclophosphamide treatment. These experiments were performed in both SPF white leghorn chickens and commercially available broilers with passively acquired maternal antibodies. Our data demonstrate that the virus is controlled in the absence of actively produced antibodies, and is independent of B lymphocytes. This suggests that cellular immunity is sufficient for protection of broilers with maternal antibodies against reovirus infection following early age vaccination with live reoviral vaccine.