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T-Cell suppression by cyclosporin-A enhances infectious bursal disease virus infection in experimentally infected chickens

In this study, the role of T lymphocytes was investigated in chickens experimentally infected with infectious bursal disease virus (IBDV). Chickens were treated with cyclosporin-A (CS-A), a selective T-cell suppressant drug, by the intramuscular route, starting 3 days before virus infection and every third day thereafter,and infectious bursal disease pathogenesis was compared in such T-cell suppressed and intact chickens using a vaccine strain; namely, Georgia and a field isolate of IBDV. Treatment of chickens with CS-A caused a significant suppression of phytohaemagglutinin-A specific proliferative responses of peripheral blood mononuclear cells. The virus neutralizing antibody titres in such CS-A treated chickens were not suppressed. T-Cell suppression resulted in an increase in the severity of gross lesions caused by IBDV and extensive muscular haemorrhages were observed in such chickens between 15 and 21 days post-inoculation. Similarly, there was a marked increase in the severity of infectious bursal disease-specific microscopic lesions in the bursa of T-cell suppressed chickens. Consistently higher titres of virus were observed in bursa of CS-A treated chickens. Virus titres were 1 to 2 log10 higher in the T-cell suppressed chickens as compared with the intact ones. These studies suggest that T cells play a role in limiting the IBDV infection.