INTEGRIN-ASSOCIATED PROTEIN (IAP, ALSO TERMED CD47) IS INVOLVED IN STROMA-SUPPORTED ERYTHROPOIESIS

Erythropoiesis is regulated by the hematopoietic microenvironment of t he spleen, fetal liver, and bone marrow in mice, We previously showed that established stromal cells from these organs selectively support e rythropoiesis in vitro. To identify the cell surface molecule(s) on th e stromal cells involved in erythropoiesis, we raised monoclonal antib odies (MAbs) to MSS62 stromal cells derived from newborn spleen and ob tained MAb-100.1, which partially inhibited the stroma-supported eryth ropoiesis in vitro. Using an expression cDNA library of MSS62 cells, w e cloned a gene encoding the protein recognized by MAb100.1 and identi fied it as integrin-associated protein (IAP, also termed CD47), which may play a general role in integrin-mediated signal transduction. IAP/ CD47 is expressed in the stromal cells of spleen, fetal liver, and bon e marrow, and in a variety of hematopoietic cells including erythrobla sts. Thus, IAP may be partly involved in the erythropoietic supporting ability of the stromal cells.