Studies on thymocyte subpopulations in guinea pigs. 2. Three subpopulations differing in rosette-forming ability, as detected by both visual and electronic counting of rosettes.

Rosette-forming cells were counted in three thymocyte subpopulations separated by density gradient centrifugation with Percoll. A method for the electronic counting of rosettes is described which resulted in excellent agreement with results of visual counting. By both methods, significant differences in the rosette-forming ability of the studied subpopulations were detected. Thus, in population Ia, earlier shown to consist of large cells of low density and with high spontaneous proliferative activity, the rosette frequency was 54% as compared with 70% in the whole thymus population and 83% in population II, known to consist of small, immunologically incompetent cells. The third population studied (Ib), consisting of intermediate density cells, had 74% rosette-forming cells.