Differential antibody responses in 6.B major histocompatibility (B) complex congenic chickens

Lines 6.6-2 (B2B2) and 6.15-5 (B2B2), congenic for the major histocompatibility (B) complex with > 99.9% background gene uniformity, were used to examine primary antibody responses to two antigens. In each of two trials, 1 mL of 5% SRBC, a T cell-dependent antigen, or 0.1 mL of Brucella abortus (BA), a T cell-independent antigen, was injected into separate groups of each B genotype aged 3 and 6 wk. Blood samples were taken from the chickens 7 d after immunization. Serum titers (log2) for both total antibody and mercaptoethanol (ME)-sensitive antibody to detect IgG were assayed by microtiter procedures. Least squares analysis of variance and Fisher's protected Least Significant Difference at P < 0.05 were used to evaluate the data. The total anti-SRBC antibody titer was significantly higher in B5B5 chicks than in B2B2 chicks at 4 and 7 wk of age. There was no significant difference in ME sensitive antibody to SRBC. Chicks of the B5B5 genotype also had significantly higher total and IgG antibody titers to BA at both ages than B2B2 chicks. The results indicate that 4- and 7-wk-old B5B5 chicks had a significantly stronger antibody response to SRBC or BA than B2B2 chicks.