Analysis of the protective effect of the haemagglutinin-neuraminidase protein in Newcastle disease virus infection

The role of immune responses to haemagglutinin-neuraminidase (HN) protein in protection against a Newcastle disease virus (NDV) infection was investi-gated using a recombinant vaccinia virus expressing HN (HN-RVV). Live HN-RVV replicated inchickens and completely protected them from lethal infection with virulent NDV. Inactivated HN-RVV also pro-tected chickens when administered with adjuvant but not when administered without adjuvant. However, large amounts of the inactivated HN-RVV (100-fold excess) without adjuvant provided protection. Specific antibodies against the HN protein of NDV were detected in sera from survivors but not from dying birds. However, the kinetics of antibody responses in chickens inoculated with live HN-RVV and inacti