Participation of radioresistant Forssman antigen-bearing macrophages in the formation of stromal elements of erythroid spleen colonies.

Using immunohistological methods with anti-Forssman glycosphingolipid antiserum and F4/80 monoclonal antibody, we investigated the dynamics of stromal macrophages during the development of haematopoietic spleen colonies in lethally irradiated adult mice which had been transplanted with syngeneic bone marrow cells. After irradiation, the spleen had shrunk and both Forssman +F4/80+ and Forssman-aggregated F4/80+ macrophages tended to aggregate in the red pulp. On the other hand, after irradiation and transplantation, discriminate erythroid foci developed in the shrunken splenic red pulp and both types of aggregating macrophages, which were involved in the foci, began to extend their cytoplasmic processes. Later, the macrophages distributed themselves within the enlarged erythroid colonies and showed fine cytoplasmic extensions among erythroblasts. We also examined the occurrence of stromal macrophages in the haematopoietic foci during spleen development. While Forssman + macrophages were scarcely present at birth when erythropoietic activity had already occurred, many F4/80+ macrophages were observed. Forssman + macrophages gradually increased in number up to 3 weeks after birth. The results clearly demonstrated heterogenicity of stromal macrophages in haematopoietic foci.