Regulation of L-selectin expression on cultured bone marrow leukocytes and their precursors

Abstract

L-selectin (LECAM-1, LAM-1, MEL-14 antigen, Dreg antigen) is one of the molecules controlling lymphocyte homing from the blood to peripheral lymph nodes and granulocyte adhesion to inflamed endothelium. In this work, regulation of L-selectin expression on mouse bone marrow cells was studied. L-selectin-negative cells were isolated by panning technique, cultured for 1-7 days with cytokines and mitogens, and L-selectin expression was analyzed by immunofluorescence staining. When cultured for 3 days with interleukin (IL) 1, IL 2, IL 5, IL 6, phytohemagglutinin, pokeweed mitogen or in the medium alone, 75%-85% of L-selectin-negative large cells (including granulocytes, macrophages/monocytes, blasts and their precursors) became L-selectin positive. In contrast, IL 3, IL 4, granulocyte-macrophage colony-stimulating factor (GM-CSF) and lipopolysaccharide (LPS) prevented the induction of L-selectin in a time- and dose-dependent manner. GM-CSF was the most potent inhibitor and only 10%-15% of cells became L-selectin positive after 3 days of culture. Furthermore, L-selectin was down-regulated on cultured unselected bone marrow cells by IL 3, IL 4, GM-CSF and LPS stimulation. After culture, the relative molecular mass of L-selectin was 100 kDa, similar to the size of the granulocyte form of this antigen. Cultured cells adhered to high endothelial venules (HEV) only 10%-32% as effectively as freshly isolated bone marrow cells despite high levels of L-selectin expression. The phenotypic analysis and the HEV binding data indicate that after culturing L-selectin was almost exclusively expressed on bone marrow leukocytes of myeloid series, and on these cells it was not functional in mediating peripheral lymph node HEV binding. Overall, these results show that the expression of L-selectin can be modulated by regulating the maturation and differentiation of the cells in vitro. This supports the idea that different cytokines and mitogens may also be important in controlling migrational status of leukocytes in vivo.