Virus-induced immunosuppression in chickens.

Reovirus and infectious bursal disease virus are among the naturally occurring viruses that cause immunosuppression in chickens. Both viruses cause necrotic lesions in the bursa of Fabricius and may destroy B cells. This may explain their ability to cause humoral immune suppression. The mechanism(s) of virus-induced suppression of cellular immunity is not well understood. Both viruses inhibit the mitogenic response of T cells in chickens. We have noted that this inhibition may be mediated by inhibitory cytokines such as transforming growth factor-beta and nitric oxide produced by activated macrophages. Preliminary studies have indicated that pretreatment of chickens with an immunomodulator, acemannan, reduced the reovirus-induced inhibition of T cells.