Recovery of antibody-producing ability and lymphocyte repopulation of bursal follicles in chickens exposed to infectious bursal disease virus

We studied the long-term effect of infectious bursal disease virus (IBDV) i n chickens. Specifically, the restoration of virus-induced bursal lesions a nd the duration of humoral immunodeficiency were examined. One-week-old spe cific-pathogen-free chickens were intraocularly inoculated with an intermed iate vaccine strain (IBDV-Vac) or a virulent strain (IM-IBDV). At intervals postinoculation (PI), chickens were examined for histopathologic lesions. At 1, 3, 5, 10, or 15 wk PI, the chickens were injected with a mixture of a ntigens, and primary antibody responses were examined at 10 days postimmuni zation. Initially, the virus caused extensive necrosis of bursal B lymphocytes. Thi s lesion was accompanied by an infiltration of T lymphocytes. With time, th e necrotic lesion in the bursa was resolved. The follicles became partly re populated with B lymphocytes. The repopulation occurred faster in the chick ens exposed to IBDV-Vac than in the chickens exposed to IM-IBDV. By 7 wk PI , 40% and 80% of bursal follicles in IM-IBDV- and IBDV-Vac-inoculated chick ens, respectively were repopulated with immunoglobulin Mf B lymphocytes. Bo th IBDV-Vac and IM-caused suppression of the primary antibody response to a ntigens. However, the antibody responses of the chickens exposed to either of the two IBDV strains used were compromised only during the first 6 wk of virus exposure. Subsequently, the antibody response returned to near norma l levels.