Development of CD4+ Macrophages from Intrathymic T Cell Progenitors Is Induced by Thymic Epithelial Cells

Abstract

It was recently demonstrated that there are CD4+ macrophages, which exhibit strong phagocytic activity, in the thymus. They are suggested to play an important role for the elimination of apoptotic thymocytes. However, the origin and nature of CD4+ macrophages in the thymus remain unexplored. In this study, we describe that the most immature intrathymic progenitors (CD25−/CD44+/FcR+) give rise to CD4+ macrophages by oncostatin M-responsive thymic epithelial cells (ORTEC) in an IL-7-dependent manner. Neither conditioned medium of ORTEC nor a mixture of cytokines induced CD4+ macrophages, and oncostatin M receptor was not expressed in thymocytes, suggesting that the development of CD4+ macrophages from the immature thymocytes requires a direct interaction with ORTEC. These results collectively suggest that the development of CD4+ macrophages from the intrathymic T cell progenitors is induced by thymic epithelial cells.