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 periphe ral blood, and at 14 weeks of age in the bursa of Fabricius, spleen an d thymus of two lines of chicken that had been selected over 13 genera tions for either high (H) or low (L) antibody responses to sheep red b lood cells (SRBC), and also in a randombred control (C) line. Flow cyt ometry showed no consistently significant differences between the thre e lines in numbers of circulating lymphocytes and other leukocytes aft er hatching. However, higher percentages of CD4(+) cells and B cells w ere 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 t he distribution of CD4(+) or CD8(+) cells in the various tissues at 2 and 7 days after immunization. These results suggest that previously r eported differences in in vivo immune responses between these chicken lines may be related to the differences in resident T-lymphocyte subpo pulations in the lymphoid tissues. The involvement of T-cell subsets a nd non-antigen-specific mechanisms in divergent selection on humoral i mmune responses in chickens is discussed.