Genetic line and major histocompatibility complex effects on primary and secondary antibody responses to T-dependent and T-independent antigens

The effects of MHC and nonMHC (background) genetics on the kinetics of prim ary and secondary antibody responses to T-cell-dependent (SRBC) and T-cell- independent [Brucella abortus (BA)] antigens were investigated. Eight genet ic groups were represented, with four homozygous MHC haplotypes [B-1-lrGAT( low) (IrGAT = immune response to GAT locus); B-1-IrGAT(high); B-19-IrGAT(lo w); B-19-IrGAT(high)] on two genetic backgrounds, the SI and G lines, Birds were injected simultaneously with BA and SRBC at 4 and 7 wk of age, and bl ood samples were taken weekly from 4 to 10 wk of age for measurement of tot al agglutinating serum antibody levels. A quadratic equation and its first derivative were computed for each bird to approximate individual curve para meters: y max, the maximum titer; t max, the time required to achieve y max ; and c coefficient, the rate of decline in the titer. Curve parameters of birds from different lines were analyzed separately by using the General Li near Model procedure. A second analysis that included line effect evaluated the nonMHC gene effects and their interactions with erythrocyte antigen B locus (Ea;B) or IrGAT. In the S1 line, there was an interaction (P < 0.05) between MHC haplotypes and sex for primary response to BA. In contrast, the re were no significant main effects nor interactions in the G Line backgrou nd for primary and secondary responses to BA and SRBC. There was an effect (P < 0.05) of line background on y max for primary BA and for secondary SRB C responses. A positive correlation (P < 0.05) was found between the c coef ficients of BA and SRBC secondary responses, suggesting that the Tate of de cline in the secondary response is similar between these T-dependent and T- independent responses. The overall results of this study indicate complex i nteractions between specific MHC alleles and the nonMHC background of the L ines in which they are studied.