Immune response and resistance to infectious bursal disease virus of chicken lines selected for high or low antibody response to Escherichia coli

Two experimental broiler lines were developed by divergent selection for hi gh (HH) and low: (LL) antibody response to Escherichia coli. Antibody:respo nse of these lines to immunization with a commercial vaccine (whole inactiv ated virus, WIV) against infectious bursal disease virus (IBDV) or with pro teins VP2 and VP3 of that virus, and their resistance to challenge wi th a. virulent IBDV, were tested. The study was performed with 213 male and fema le chicks from the tenth generation of the HH and LL lines. At 15 d of age, after disappearance of maternal antibodies, chicks from each line were ran domly divided into four groups and injected with WIV, VP2, VP3, or adjuvant alone as a negative control. Chicks were bled 18 d postinjection, and anti body titers were determined by ELISA. Ten days later, the chicks were chall enged with a virulent strain of the virus and killed after 10 d; the ratio of bursa of Fabricius to 100 g BW was determined for each bird. Significant differences in antibody titers were found among immunized and control chic ks. Chicks from the HH line exhibited significantly higher antibody titers than LL chicks in response to WIV and VP2 vaccines but not to VP3 vaccine. Following challenge, bursa weight (relative to BW) of HH and LL chicks vacc inated with WIV and VP2 was significantly higher (P < 0.01) than that of ch icks vaccinated with VP3 or the challenged unvaccinated control. No differe nce was found in this parameter between the latter two groups. Possible exp lanations for the differences in the line response to VP2 and VP3 are discu ssed.