Humoral and cellular immune response of sheep to bluetongue virus

Plaque cloned strains of the 4 US bluetongue (BT) virus (BTV) serotypes (10, 11, 13 and 17) were pathogenic to sheep and induced mild clinical responses. The clinical responses coincided with the highest titer of viremia reached by day 7 following primary infection. The 4 BTV strains were immunogenic, inducing group-specific (precipitating) and type-specific (neutralizing) antibodies. Primary infection induced an immune response which protected the animals against secondary challenge with the homologous virus. Peripheral blood lymphocytes (PBL) obtained from infected animals responded specifically to in vitro stimulation with pure BT viral antigens. PBL responded to both homologous and heterologous BTV antigens indicating a cross-reactive nature of the lymphocyte response. Perturbations were observed in PBL response to in vitro stimulation with the mitogens phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM). The response to mitogens was depressed transiently following primary infection and secondary challenge. A significant increase was reached by 3 weeks following primary infection and then gradually leveled off to normal. The specific stimulation of PBL in response to viral antigens and the increase in response to mitogens, as in vitro correlates of cell mediated immunity (CMI), were suggested to play a role in the clearance of BTV infection. Immunoblotting was applied to characterize the specificity of the serologic response to BTV. Sheep antisera to BTV detected 11 specific viral proteins. The maximum response on day 28 post inoculation (PI) detected 11 proteins including both the major and minor protein components.(ABSTRACT TRUNCATED AT 250 WORDS)