Role of the immune system in bluetongue host-viral interactions.

Immune responses involving both B and T lymphocyte subpopulations have been demonstrated in sheep and cattle. The immune responses appear to be associated with the modulation of disease expression in sheep and cattle. An immature immune system in fetal lambs and calves permits virus to replicate with little or no host interference. Viral teratogenicity may consequently lead to malformed newborns, fetal deaths, abortion or readsorption. Adult sheep and cattle appear to respond somewhat differently to bluetongue virus (BTV). In both species T cell or cell mediated (CMI) and B cell or humoral mediated immunity (HMI) occur. There is a correlation between CMI response and protective immunity in sheep. Although these responses occur in cattle it appears that an IgE mediated hypersensitivity leads to expression of clinical disease and suppressive modulation of protective immunity.