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

Lines 6.6-2 ((BB2)-B-2) and 6.15-5 ((BB2)-B-2), 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 (log(2)) 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 (BB5)-B-5 chicks than in (BB2)-B-2 chicks at 4 and 7 wk of age. There was no significant difference in ME-sensitive antibody to SRBC. Chicks of the (BB5)-B-5 genotype also had significantly higher total and IgG antibody titers to BA at both ages than (BB2)-B-2 chicks. The results indicate that 4- and 7-wk-old (BB5)-B-5 chicks had a significantly stronger antibody response to SRBC or BA than (BB2)-B-2 chicks.