Effect of genetic selection and MHC haplotypes on lymphocyte proliferation and Interleukin-2 like activity in chicken lines selected for high and low antibody production against sheep red blood cells

Abstract

Chickens from third generation matings of lines of chickens selected for high (HA) and low (LA) antibody production to sheep red blood cells (SRBC) and typed for MHC genotypes B 13/13, B 13/21, and B 21/21 were used in this study. Chickens from both lines carried all the three genotypes B 13/13, B 13/21, and B 21/21. To study T- and B-lymphocytes mitogenic activity, 12-week-old female chickens were injected intravenously with 0.2 ml of 9% SRBC and spleens were collected at 0, 6 h, and 6 day post-antigen injection (pAg). Isolated lymphocytes were incubated with either Concanavalin-A (Con-A) for T-cell activity, or Pokeweed mitogen (PWM) for B-cell activity and thymidine 3 H uptakes were measured. To study the Interleukin-2 (IL-2)-like activity in the same lines and genotypes, splenic lymphocytes from 12-week-old chickens were passed through nylon wool columns to enrich the T-cell population. After a 24 h incubation with Con-A, the conditioned media (CM) were collected. The CM were tested for IL-2 like activity by determining whether they altered the proliferation of Con-A stimulated T cells. This proliferation effect was then compared to that of a reference conditioned media (RCM) prepared from K-strain birds and that were used as the standard for the assay. There was no significant difference ( p > 0.05) in IL-2 like activity between HA and LA lines, however, the LA was significantly higher than HA ( p < 0.05) in T- and B-cell mitogenic activity. The genotype B 13/13 had significantly higher ( p < 0.05) IL-2 like activity than the B 21/21. The genotype B 13/13 was also significantly higher ( p < 0.05) in T- and B-cell mitogenic activity than the B 21/21. At 0 h, pAg T- and B-mitogenic activity was significantly higher ( p < 0.05) than 6 h. In summary, our results indicate that although the birds were selected for high antibody production to SRBC, their lymphocyte mitogenic activity was lower than those selected for low antibody production. Hence, humoral and cell-mediated immune responses appear to be under different genetic controls, and that selection for greater humoral response may be at the expense of cellular responses. Our results also suggest differences in IL-2 like activity production between chickens carrying different MHC B-haplotypes, and that genetic control of such activity is possibly linked to the MHC genes.