ANTIGEN-SPECIFIC LYMPHOPROLIFERATIVE RESPONSES TO TETANUS TOXOID - A MEANS FOR THE EVALUATION OF MAREKS-DISEASE VIRUS-INDUCED IMMUNOSUPPRESSION IN CHICKENS

Antigen-specific lymphoproliferative responses were examined in chicke ns following immunization with tetanus toroid (Ttx). The immune compet ence of chickens was assessed by mitogen assay utilizing phytohemagglu tinin (PHA)-stimulation and Ttx-specific antigen proliferation assay ( Ttx-APA). Immune spleen cells but not peripheral blood leucocytes demo nstrated specific proliferation following stimulation in vitro in a Tt x-APA. In this study, we examined firstly the effects of Marek's disea se (MD)associated immunosuppression on specific immune responses. The humoral and cell-mediated immune responses were monitored by enzyme-li nked immunosorbent assay (ELISA) and Ttx-APA, respectively. Secondly, we examined if vaccination against MD using a conventional herpesvirus of turkeys (HVT) vaccine and two recombinant HVT (rHVT) vaccines woul d affect the development of Ttx-specific immune responses. The rHVT va ccines used in this study included two constructs: one expressing both Newcastle disease virus (NDV) and MD virus (MDV) genes (HVT/NDV/MDV), and another expressing only MDV genes (HVT/MDV). The mitogenic respon ses of spleen cells of the vaccinated chickens were inconsistent allow ing no definitive conclusions about vaccinal immunosuppression. The re sults of the Ttx-APA indicated that Ttx-specific lymphoproliferative r esponses provide a meaningful measure of immunosuppression. The MDV-in duced immunosuppression resulted in the inhibition of Ttx-specific lym phoproliferation in vitro. Both HVT and rHVT vaccines were not immunos uppressive as indicated by the development of normal Ttx-specific lymp hoproliferative responses in chickens. These results indicate that vac cination against MD results not only in the prevention of tumor format ion but also protection from possible virus-induced immunosuppression. Published by Elsevier Science Ltd.