Factors influencing the appearance of antibody in tracheal washes and serum of young chickens after exposure to Newcastle disease virus.

The development of plaque-neutralizing antibody in tracheal washes and hemagglutination inhibition antibody in serum was followed after intratracheal and intranasal or intramuscular inoculation of 1-, 14-, or 28-day-old chicks with a lentogenic strain of Newcastle disease virus (NDV). Serum antibody could be detected between 7 and 10 days after intratracheal and intranasal vaccination in birds either with or without maternal antibody to NDV. However, among the 1-day-old group only birds without maternal antibody showed an antibody response after intramuscular inoculation. All birds possessing either actively or passively acquired serum antibody showed a sharp rise and subsequent decline of anti-NDV activity in tracheal washes between 4 and 10 days after intratracheal or intranasal vaccination. Using radiolabeled chicken immunoglobulin injected intravenously as a tracer, it was shown that this initial peak of anti-NDV activity in tracheal washes could be accounted for by enhanced transudation of serum antibody. The transudation of serum antibody coincided with the course of viral pathology observed in the tracheae of infected birds. Neutralizing antibody in tracheal washes beyond 10 to 14 days postvaccination was, most likely, porduced locally, in the respiratory tract.