IBV-specific cellular immune responses. A In vitro proliferations of lymphocytes from vaccinated chickens in response to the recall S1 antigen. Results are expressed as stimulation indices, defined as proliferation in response to recall antigen relative to the mock stimulated cells. Each data points represent mean ± SD of six chickens per group. B The CD3+CD4+ and CD3+CD8+ T-cell subsets in vaccinated and control chickens are expressed as a percentage of the gated cells. The data are presented as the mean ± S.D of six chickens. *p < 0.05.