Presence of viral antigens and antibody in the trachea of chickens infected with avian infectious bronchitis virus.

Following infection of chickens with infectious bronchitis virus (strain M41) viral antigens were detected by immunofluorescence in the basal layer of the tracheal mucosal epithelium for 44 days. The enzyme-linked immunosorbent assay (ELISA) first detected virus-specific antibody in tracheal washes 7 days after infection and at 10 days these antibodies reached a level that was maintained for at least 44 days, although there was considerable variation between chickens. In contrast a neutralisation test did not detect antibody until day 20 ; titres were in the range 2.2 to 3.2 log2 reaching a maximum at day 27. ELISA detected anti-viral IgA in tracheal washes only on day 7, whereas IgG was detected in all samples containing anti-viral antibody. Serum anti-viral antibodies were detected by ELISA at 7 days and reached peak titres at 10 days, which were maintained. In contrast, serum neutralising antibodies were first detected at 10 days and increased to peak titres on day 24. The implications of the differences between the results of ELISA and neutralisation tests are discussed.