DNA LIGASES AS MARKERS OF LYMPHOID-CELL MATURATION AND HETEROGENEITY IN THE CHICKEN

The activities of 8S and 6S DNA ligases were studied in the chicken lymphoid cells of blood, spleen and bursa of Fabricius at different stages of development, from late embryonic life to .apprx. 3 mo. after hatching. These cells have been sorted with the fluorescence-activated cell sorter FACS II on the basis of size and T or B antigenicity (immunofluorescence). The light 6S DNA ligase was previously demonstrated to be associated to a late stage of differentiation of thymocytes. In the bursa, a unique form of 8S DNA ligase is found during the whole period of observation. This form of enzyme remains in the B cells of the spleen until 3 wk after hatching, but is never present in the blood cells. As far as T cells are concerned, the light DNA ligase is present in the blood from 18-day embryonic life on. In the spleen T cells, on the contrary, this enzyme appears only 3 wk after hatching. Before this stage, splenic T cells are devoid of any form of DNA ligase activity. These findings show biochemical differences in T and B lymphocytes colonizing the periphery, blood and spleen, and suggest, at least for the T cells at early stages, a heterogeneity in the degree of differentiation.