MODULATION OF CELL-SURFACE ANTIGENS AND REGULATION OF PHAGOCYTIC-ACTIVITY MEDIATED BY CD11B IN THE MONOCYTE-LIKE CELL-LINE U937 IN RESPONSE TO LIPOPOLYSACCHARIDE

Modulation of the cellular antigens and regulation of the phagocytic activity of the monocyte-like cell line U937 after culture with lipopolysaccharide (LPS) were investigated. CD14 expression was induced on the surface of the U937 cells after 48 h of culture with LPS and then they became adhesive with numerous filamentous filopodia extruded on the cell surface, exhibiting the enhanced expression of CD16 and CD23, the activation cell surface markers for differentiation into macrophage. However, no induction or enhancement of the cell surface expression was observed with respect to CD11b, CD18, HLA-A, B, C, HLA-DR, DQ, DP or CD57. These U937 cells also acquired the ability to produce superoxide anions and to phagocytose the Salmonella enteritidis strain, 116-54. This phagocytosis was inhibited by the anti-CD11b monoclonal antibodies, but not by the anti-CD14, anti-CD16, anti-CD18, anti-CD23, anti-HLA-A, B, C or anti-HLA-DR monoclonal antibodies. These findings indicate that the phagocytic activity against Salmonella enteritidis 116-54 induced by LPS is mediated mainly via the CD11b molecule, but is not associated with the increased expression of CD11b. Puromycin and cycloheximide, inhibitors of protein synthesis, or a divalent cation-chelating agent, EDTA completely inhibited this phagocytic activity. Interestingly, EDTA was found to suppress specifically the CD11b expression on the U937 cells cultured with LPS. No phagocytic activity was induced when the U937 cells cultured with LPS were incubated at 4-degrees-C, but restored to the control level when shifted up to 37-degrees-C. This experimental system provides an excellent model for the investigation of the molecular mechanism underlying modulation of the cell surface antigens and regulation of the phagocytic activity mediated by CD11b in the U937 cells in response to LPS.