Ligation of N-acetylgalactosamine–containing structures on rat bone marrow cells enhances myeloid differentiation and murine granulocyte-macrophage colony-stimulating factor-induced proliferation

Previously we have reported the differentiation-dependent expression of a soybean agglutinin (SBA)-binding structure on rat bone marrow cells (BMCs) during their differentiation into macrophages (m phi s). In the present study we tried to analyze the functional role of the SBA-binding structure in BMC proliferation and differentiation. Addition of SBA to BMC cultures driven into m phi differentiation by recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF), resulted in a two- to threefold increased proliferation rate compared with rmGM-CSF alone. However, the number of colonies in methyl cellulose was not increased by SBA. The effect of SBA was dose dependent (from 4 to 83 pM SBA), with a maximum effect at 83 pM. Experiments to detect a possible synergistic effect of additional cytokines produced by BMC after SBA treatment were inconclusive. The enhancing effect of SBA was also seen when high-density cells, which did not proliferate in response to rmGM-CSF (mainly granulocytes), were removed. Therefore, SBA may increase the CSF reactivity of responsive m phi progenitor cells directly by binding to N-acetylgalactosamine residues on their surface.