Immunosuppression in specific-pathogen-free broilers administered infectious bursal disease virus vaccines by in ovo route

The effect of two infectious bursal disease virus (IBDV) vaccines (IBDV-immune complex [Icx] and IBDV-2512), administered in ovo, on the cell-mediated immunity of specific-pathogen-free (SPF) broilers was examined. A decrease (P < 0.05) in the T-cell mitogenic response occurred in birds vaccinated with both vaccines on days 9 and 21 post in ovo vaccination (PIOV), but an increase (P < 0.05) occurred on day 15 PIOV. The T cells from birds given the IBDV-2512 were less responsive. There were no significant differences in proportions of lymphocytes expressing CT4(+)CT8(-) and CT8(+)CT4(-) except on day 21 PIOV, where an increase (P < 0.05) in IBDV-2512-vaccinated birds and a decrease (P < 0.05) in percentage of CT4(+)CT8(-) in IBDV-Icx-vaccinated birds was observed. There was an increase (P < 0.05) in percentage of CT8(+)CT4(-) T cells on day 21 PIOV in both vaccinated groups. A decrease (P < 0.05) in B-cell percentage was observed on day 21 PIOV in birds given both vaccines. Results indicated that although Immoral immunosuppression is associated with destruction of B cells (bursal atrophy), cell-mediated immunosuppression induced by these two IBDV vaccines in SPF birds was not associated with altered helper (CT4(+)CT8(-)) or cytotoxic (CT8(+)CT4(-)) subpopulations of T lymphocytes.