Specific cytotoxic T lymphocytes are involved in in vivo clearance of infectious bronchitis virus.

Cytotoxic T-lymphocyte (CTL) responses to infectious bronchitis virus (IBV) were determined at regular intervals between 3 and 30 days postinfection (p.i.). The maximum response with 82% lysis of labeled target cells was detected at 10 days p.i. The specific CTL response did not begin to decline until the amount of virus, which peaked at day 8 p.i. in both the kidneys and lungs, started to decrease. Clinical respiratory signs of illness also correlated with amount of virus. CTL activity was shown to be major histocompatibility complex (MHC) class restricted because the lysis of MHC-mismatched targets was negligible, and lysis was mediated by CD8+ CD4- T cells, as the CTL response could be abolished with removal of CD8+ CD4- but not CD4+ CD8- lymphocytes. In contrast, immunoglobulin M (IgM) antibody was not detected until day 10 p.i., and levels peaked at day 12 p.i.; IgG antibody levels were minimal until day 15 p.i. but continued to increase exponentially until day 30 p.i., the last day examined. In summary, CTL responses correlated with initial decreases in infection and illness.