Cytotoxic T lymphocyte responses to infectious bronchitis virus infection.

Cytotoxic T lymphocyte (CTL) activity to infectious bronchitis virus (IBV) was examined at regular intervals between 3 and 30 days post infection (p.i.). The maximal CTL lysis of target cells infected with IBV with 82% was detected at 10 days p.i. The specific CTL activity began to decrease only after viral loads, which peaked at day 8 p.i. in both kidneys and lungs, started to decline. Therefore, the CTL response correlated with elimination of acute infection. IgM antibody did not appear until day 10 and levels peaked at day 12 p.i. whereas IgG antibody titers were detectable only by day 15 p.i., but continued to increase exponentially until day 30 p.i., the last day examined. IBV specific CTL epitope(s) were mapped within the carboxyl terminal 120 amino acids of nucleocapsid protein. In vivo inoculation of this fragment, as cDNA, induced protection against acute infection. The absence of viral neutralizing epitopes on the nucleocapsid protein would suggest that protection with known CTL eptiope(s) can be induced in the absence of neutralizing antibody.