Memory T cells protect chicks from acute infectious bronchitis virus infection.

Infectious bronchitis has remained one of the most difficult to control diseases in poultry since it was first described in 1931. Previous studies demonstrated that primary CD8(+) T lymphocytes collected at 10 days post-infection (p.i.) are important in controlling acute infection. To further investigate the role of memory T cells in protection, T lymphocytes collected from B19/B19 chicken spleens at 2, 3, 4, and 6 weeks p.i. were transferred to six-day-old syngeneic chicks one day prior to challenging with 10(6) EID(50) of the IBV Gray strain. Memory immune T cells collected at 3 to 6 weeks p.i. provided dose responsive protection from clinical illness. The greatest protection was observed after the transfer of 10(7) T cells collected at 6 weeks p.i., whereas T cells collected at 2 weeks p.i. did not protect. Annexin-V staining of the spleen cells demonstrated that the cells collected at 2 weeks p.i. were undergoing significantly more apoptosis than cells collected at 10 days p.i. Specific antibody production in sera collected at 7 days p.i. did not correlate with protection. T cell subtype depletion demonstrated that CD8(+), not CD4(+), T cells were critical. Memory T cells can be detected in peripheral blood mononuclear cells up to at least 10 weeks p.i. These results demonstrated that IBV specific CD8(+) memory T cells generated at 3 to 6 weeks p.i. can protect syngeneic chicks from acute IBV infection.