Abstract
During hematopoiesis in the bone marrow (BM), hematopoietic progenitor cells (HPC) proliferate and differentiate in intimate contact with BM stromal cells in a highly regulated interplay among cytokines, chemokines, and adhesion molecules. Using the mouse BM stromal cell line MS-5 as immunogen, we raised monoclonal antibodies (mAb) against surface proteins that could participate in interactions between HPC and stroma. Flow cytometry and immunodepletion analysis indicated that two antibodies, MA-8 and MA-2, recognized CD44. Although MA-8 and another anti-CD44 antibody, IM7.8.1, blocked adhesion of hematopoietic cells to hyaluronate, adhesion to BM stroma was notably increased by these mAb, suggesting minor roles for CD44/hyaluronate interaction and the triggering of additional adhesion pathways upon CD44 engagement. The presence of MA-8 in Dexter-type long-term BM cultures (LTBMC) only slightly inhibited production of myeloid cells, and the number of myeloid progenitors (measured as CFU-GM) in the supernatants of LTBMC performed with MA-8 was similar to those carried out with control antibodies. Instead, IM7.8.1 completely blocked myelopoiesis, whereas an anti-α4 integrin mAb increased CFU-GM amounts. In summary, two anti-CD44 antibodies with similar effects in cell adhesion showed notable differences in myelopoietic cultures, indicating the structural and functional complexity of the CD44 molecule.
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