Maternally‐derived antibody to infectious bronchitis virus: Its detection in chick trachea and serum and its role in protection

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Abstract
Chicks with maternally‐derived IgG antibodies to infectious bronchitis virus (IBV) were protected against challenge with a mixture of IBV and Escherichia coli. This protective immunity lasted for at least 1 week. IBV‐specific IgG was detected, using an ELISA, in the majority of tracheal washes taken from chicks aged 1 day and 1 week that had been hatched from IBV‐infected hens. Some of the 2‐week‐old chicks also had detectable antibody. This tracheal IgG may be an important factor in mediating protective immunity. The origin and transport of the IgG into the trachea are discussed. IBV‐specific IgG was detected in chick serum and had a half‐life of 4.5 days. Yolk samples, collected from eggs laid by IBV‐infected hens, were tested for the presence of viral‐specific IgG antibodies. The sequential IgG antibody response to IBV in yolk was determined. Specific antibodies were detected at highest concentrations 16 to 18 days after infection and then declined. A second inoculation of an inactivated oil‐based vaccine induced high concentrations of IBV‐specific antibodies in the yolk which were maintained for the 60 days of the experiment. Detection of specific IgG in the yolk could be used as a means of assessing response to vaccination.