Turnover of ED2-expressing macrophages in the thymus cortex of rats

To investigate the turnover of thymic ED2⁺ cortical macrophages, vascular thymus transplantation in RT7-congenic rats were performed. Thymus graft cell suspensions were analyzed using ED2 in combination with congenic markers. Immunohistology of thymus graft sections was performe to demonstrate the immigration and persistance of these macrophages at several time points after transplantation. In contrast to other mobile thymus cells like thymocytes and interdigitating cells, most ED2⁺ cortical macrophages showed a slow turnover rate. At 76 days after transplantation more than 30% of ED2⁺ macrophages were still of donor origin. The migration properties of these macrophages are discussed in relation to their presumed tole in thymocyte maturation and proliferation.