Immunology, Health, and Disease: Immunology I

Major histocompatibility complex (Mhc) genes produce significant effects on immune responses . In addition, genes outside the Mhc influence immunity . USDA inbred chicken lines 63 and 72, differ in immune characteristics including immune organ size, immunoglobulin levels, immune cell subset distribution, mitogen-induced lymphoproliferation as well as responses against Marek’s disease virus, Rous sarcoma virus and v-src DNA tumors . Lines 63 and 72, both having the B2B2 Mhc genotype, were used to develop recombinant congenic strains (RCS) to facilitate identification of non-Mhc genes that affect immune responses . Line 63 females were crossed to Line 72 males plus 2 backcrosses to Line 63 with subsequent brother-sister mating generated 19 RCS designated by letter, each having a different 87 .5% Line 63 and 12 .5% Line 72 . Line 63, Line 72, and 19 RCS chicks in 2 replicates were injected with 0 .1 mL 0 .25% SRBC at 5 weeks of age . Antibody titers were measured in serum collected at d 0, 5, and 12 d post-injection using a microtiter method . Titers were read at 24 h . Next, the data were entered into the quadratic model described by Siegel and associates (Poult . Sci . 63:1892, 1984) . In that procedure, the d 0, d 5 and d 12 titers are used to calculate a quadratic equation for each bird (Y = a + bX − cX2) . This equation’s first derivative (dx = b − 2cX) determines the day of maximum titer. Substituting that value allowed calculation of the maximum titer and c coefficient, which is the rate of titer decline, for each bird. Bonferroni’s method (P < 0.05) was used to separate significant means. Comparing values to the 2 .49 log2 overall mean, peak antibody titer was significantly lower in RCS J (0 .6 log2) and significantly higher in RCS X (3.6 log2) . Day of peak did not differ significantly among Line 72, Line 63, and the 19 RCS. The overall mean rate of titer decline (c coefficient) differed significantly for RCS J and N. Genetic comparisons of Line 72, Line 63 and RCS will help to identify non-Mhc genes that have significant effect on antibody responses .