Regulation of Forssman antigen expression during maturation of mouse stromal macrophages in haematopoietic foci.

During a trial to develop a monoclonal antibody (mAb) specific to stromal macrophages (M phi) in haematopoietic foci, we have created a mAb, designated F10, that stains the stromal M phi more selectively than any other mAb reported. As F10 was found to react with Forssman glycosphingolipid (GSL) specifically and to give clearer immunostaining than anti-Forssman GSL IgG, we have studied Forssman antigen expression during maturation of the stromal M phi in splenic haematopoietic foci using F10 and a system of allogenic bone marrow transplantation which allows us to know the turnover of the stromal M phi in vivo. C3H/He mice (H-2k) were lethally irradiated and intravenously infused with the bone marrow cells of BALB/c nu-nu mice (H-2d). Splenic frozen-sections and cytocentrifuge preparations of splenic haematopoietic clusters from the recipient mice were stained with F10 and with mAb against major histocompatibility class I antigens. H-2d-type stromal M phi began to appear in the haematopoietic clusters at Week 5 and they gradually replaced H-2k-type stromal M phi. The percentage of Forssman+ stromal M phi gradually decreased and reached a nadir at Week 6, when most stromal M phi were already of the donor type. At Week 8, however, Forssman+ stromal M phi levels returned to normal. The delayed expression of Forssman antigen on the stromal M phi in haematopoietic foci following genotypic conversion suggests that Forssman antigen is regularly expressed on the subpopulation of stromal M phi, which mature well under specific microenvironmental factors in vivo.