Studies on Thymocyte Subpopulations in Guinea Pigs

Thymocytes were separated according to increasing buoyant density into the three subpopulations la (25% of recovered cells), lb (20%) and II (55%), and according to binding to peanut agglutinin (PNA) into PNA+ (65 %) and PNA– cells (35 %). The frequency of PNA+ was 56% in la, 60% in lb and 66% in population II. Electronic cell volume determinations disclosed mean volumes of 160 fl for la, 130 fl for lb and 100 fl for population II. PNA+ and PNA– cells were very similar as regards cell volume. Thus, PNA+ and PNA– cells are remarkably uniformly distributed among cell categories of different density and cell volume. The rapidly cycling thymocytes, regarded as the most immature cells in the thymus, and the target cells for a thymocyte growth factor both belonged to the PNA+ cells of population la. The mitogen-responsive thymocytes also belonged to population la, but were PNA-. The largest subpopulation of thymocytes, apparently corresponding to the small, non-cycling cortical cells, were recovered as PNA+ cells of population II.