Adaptive immune response of poultry to Newcastle disease vaccines.

Newcastle disease (ND), caused by virulent Newcastle disease virus (NDV), poses a major global threat to the poultry industry. ND vaccines have been used for nearly 70 years for disease prevention and control, and much is known about adaptive immune responses to infection and vaccination. However, our current knowledge remains incomplete and biased. While humoral immunity, especially regarding the induction of hemagglutination-inhibiting and virus-neutralizing antibodies, has been studied extensively, research on mucosal and cellular immunity has been more limited, despite their critical roles in restricting and clearing viral infection. Furthermore, fundamental questions persist even for humoral responses, such as the role of antibodies against viral internal proteins, the mechanisms of virus neutralization by antibodies, and the effect of antibody production on viral evolution. This review systematically summarizes existing knowledge on adaptive immunity to NDV infection, encompassing humoral, mucosal, and cellular aspects. It also highlights key gaps in our understanding of immune responses in poultry, which is important for developing novel vaccines and control strategies.