Avian infectious bronchitis in specific-pathogen-free chickens: quantitation of serum immunoglobulins by electroimmunoassay.

Immunoglobulin (Ig) levels in serums of individual 6-week-old specific-pathogen-free (SPF) chickens differed markedly. Quantitation by electroimmunoassay showed that the IgG level was quite low at 6 weeks of age (1.3 +/- 0.67 mg/ml), increased gradually with maturity, and by 16-18 weeks of age was 2.6 +/- 1.5 mg/ml. IgM levels were less variable during the same observation period (6-18 weeks, 2.4 +/- 0.50 to 2.2 +/- 0.86 mg/ml). IgA was high initially and decreased with age (6-18 weeks, 0.74 +/- 0.78 to 0.26 +/- 0.06 mg/ml). Single intratracheal vaccination with a moderate dose of live avian infectious bronchitis virus (IBV) and subsequent challenge-exposure with live virus via the respiratory tract did not markedly affect Ig levels. Birds vaccinated parenterally 2 or 3 times with live or killed IBV vaccines had a marked increase in serum IgG after similar challenge-exposure. IgA and IgM levels in vaccinated SPF birds approximated those in control SPF birds throughout the experimental period.