T cell infiltration in IBDV-infected bursa. SPF chickens were inoculated with 104EID50 of cIBDV or vIBDV and bursal tissues were collected at PID 3, 5 and 7. (A) Bursal sections from virus-free chickens (a, b and c; 20X), vIBDV-infected bursa (d, e, and f; 20X) and cIBDV-infected bursa (g, h, and i; 20X) were examined for the presence of T cells by immunohistochemistry using anti-chicken CD3+ monoclonal antibody. Brown color indicates the positive staining. (B) T cells were counted (40X) at PID 3, 5 and 7. The values represent the mean ± SEM of 5 fields/bursa/chicken on designated PID. #Statistically significant differences between control and vIBDV- or cIBDV-infected groups (p < 0.05). *Statistically significant differences between vIBDV- and cIBDV-infected groups (p < 0.05).