Con A response and interleukin 2 receptor expression of thymocytes rosetting with phagocytic cells of the thymic reticulum

Thymocytes bind to the phagocytic cells of the thymic reticulum (P-TR) and spontaneously forming rosettes were isolated and characterized. Rosetting thymocyte subsets included cells expressing different surface phenotype: most of them (91%) were of the double positive L3T4+ Lyt-2+ phenotype; a minor subpopulation (2.4%) expressed the helper L3T4+ Lyt-2- phenotype and finally a small subpopulation (6.3%) was negative for both L3T4 and Lyt-2 markers. Although the rosetting thymocytes were not enriched in mature single positive cells as compared to the non rosetting population, they showed a higher responsiveness to ConA plus recombinant IL-2. Moreover the rosetting thymocytes were induced to express IL-2 receptors just after stimulation with ConA whereas co-stimulation with ConA plus IL-2 was essential for the generation of IL-2 receptors on the non rosetting and total thymocytes. The possibility that the rosetting thymocytes acquired this activity during the rosetting process is discussed.