DIFFERENCES IN DISTRIBUTION OF LYMPHOCYTE ANTIGENS IN CHICKEN LINES DIVERGENTLY SELECTED FOR ANTIBODY-RESPONSES TO SHEEP RED-BLOOD-CELLS

The proportion of cells showing differentiation antigens specific for T cells, B cells and leukocytes was studied at various ages in peripheral blood, and at 14 weeks of age in the bursa of Fabricius, spleen and thymus of two lines of chicken that had been selected over 13 generations for either high (H) or low (L) antibody responses to sheep red blood cells (SRBC), and also in a randombred control (C) line. Flow cytometry showed no consistently significant differences between the three lines in numbers of circulating lymphocytes and other leukocytes after hatching. However, higher percentages of CD4(+) cells and B cells were present in the spleen and thymus from the H line compared with the L line. However, the L line was characterized by a higher proportion of splenic CD8(+) cells and spleen cells expressing gamma-delta T-cell receptors. Immunization with sheep red blood cells had no effect on the distribution of CD4(+) or CD8(+) cells in the various tissues at 2 and 7 days after immunization. These results suggest that previously reported differences in in vivo immune responses between these chicken lines may be related to the differences in resident T-lymphocyte subpopulations in the lymphoid tissues. The involvement of T-cell subsets and non-antigen-specific mechanisms in divergent selection on humoral immune responses in chickens is discussed.