Qualitative and quantitative studies on mixed homologous chicken thymus cell cultures.

The proliferative interaction of mixed homologous chicken thymus cells was studied in a serum-free culture system using thymus cell populations from thymus glands that had been experimentally manipulated to yield varying proportions of lymphocytes from the medulla and cortex of the gland. It could be demonstrated that the proliferative responsiveness of thymus cells to immuno-genetically different cells resided with the lymphocyte population located in the medulla of the thymus. The capability of medullary thymus cells to participate in a mixed lymphocyte interaction (MLI) was found to be nearly equal to that of splenic lymphocytes. The in vitro survival of medullary thymus cells was markedly superior to cortical thymus cells. Kinetic studies with medullary thymus cells revealed that the proliferative response in the MLI was initiated during the first 24–40 hr culture period and generally reached its peak 4 days after culture initiation. It could be demonstrated that responding cells were capable of several repeated divisions. In addition, previously nondividing cells entered the reaction for the first time up to the 3rd and possibly 4th day after culture initiation. Calculations revealed that 0·7–1·9% of the original viable thymus cell population participated in the response. It was also calculated that peripheral blood lymphocytes contaminating the thymus cell populations of both cell donors contributed less than 1% to the total number of responding thymus cells. When the response of mixed homologous thymus cells was compared in a chemically defined and serum containing medium, striking differences in the time course and magnitude of the reaction were seen. It could be shown that the viability and proliferation of thymus cells was adversely affected by serum and markedly enhanced by insulin supplementation to a chemically defined medium.