Infectious bronchitis virus antibodies in tears and their relationship to immunity.

Antibodies to infectious bronchitis virus (IBV) in chicken tears were investigated to determine if they could be used as an indicator of protective immunity. Antibody production in tears and serum was measured by enzyme-linked immunosorbent assay (ELISA) in specific-pathogen-free (SPF) white leghorn and broiler chickens vaccinated with a live attenuated vaccine containing the Massachusetts (Mass) Connaught strain of IBV. The effect of virulent infectious bursal disease virus (IBDV) infection on antibody production in tears was also evaluated. Immunity was assessed by challenging the chickens with Mass 41 and performing tracheal swabbings 5 days later. In addition, tears were also evaluated for virus-neutralizing (VN) antibodies to IBV. Following eyedrop vaccination, anti-IBV antibodies were consistently detected by ELISA in tears prior to and in higher concentrations than in the sera of SPF white leghorn and broiler chickens. Maternal IBV antibodies were present in the tear secretions of broiler chickens but in lower concentrations than in sera. Infection of SPF chicks with a virulent and immunosuppressive strain of IBDV at 1 day of age greatly reduced IBV ELISA antibody production in tears as well as serum compared with infection of chickens with IBDV at 14 days of age. IBV ELISA and VN antibody levels in tears were not accurate indicators of IBV immunity as determined by challenge with Mass 41. High tear IBV antibody titers were observed in some chickens determined to be susceptible to IBV challenge and low tear titers were detected in some protected chickens. This finding suggests that mechanisms other than antibody-mediated immunity in tears are important in viral clearance following challenge.