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Published on: September 9, 2014
Bacterial lipopolysaccharide, phorbol myristate acetate, and muramyl dipeptide stimulate the expression of a human
Abstract:
Exposure of mononuclear phagocytes to bacterial lipopolysaccharide (LPS), phorbol myristate acetate (PMA), or muramyl dipeptide (MDP) is known to stimulate a variety of cellular activities that include increases in phagocytosis, oxidative metabolism, synthesis and secretion of monokines, and cytotoxicity of microbes and tumor cells. We now report that culture of human peripheral blood monocytes in medium containing LPS, phorbol compounds, or MDP also results in the acquired expression of a plasma membrane antigen. Mo3e, as identified by a murine monoclonal antibody. Mo3e is barely detectable (by immunofluorescence flow cytometry) on freshly isolated monocytes, but is expressed in high antigen density after exposure of cells to E. coli, Salmonella minnesota, or Serratia marcescens LPS (at concentrations exceeding 0.1 ng/ml), PMA (and other biologically active phorbol compounds) (0.5 to 1 X 10(-8) M), or MDP (0.01 to 1 X 10(-6) M). Mo3e expression stimulated by LPS is prevented by pretreatment of LPS with polymyxin B, suggesting that the lipid A portion of LPS is responsible for Mo3e induction (polymyxin B has no effect on Mo3e expression stimulated by PMA or MDP). Culture of monocytes in medium containing protein synthesis inhibitors (or at 4 degrees C) blocks the acquisition of Mo3e. Recombinant IFN-gamma, which is also known to "activate" mononuclear phagocytes, does not stimulate Mo3e expression, although both LPS and IFN induce enhanced expression of monocyte Ia antigen. Analogous to their stimulatory effect on monocytes, LPS and PMA induce Mo3e expression by the human monocytic cell line, U-937. On the basis of these observations, Mo3e may represent an immunologic marker for monocyte activation stimulated in vitro by LPS, PMA (and related compounds), and MDP.
Insights
Bacterial lipopolysaccharide (LPS), phorbol myristate acetate (PMA), and muramyl dipeptide (MDP) induce a new plasma membrane antigen, Mo3e, on human monocytes. This Mo3e antigen may serve as a marker for monocyte activation in laboratory settings.
Area of Science:
- Immunology
- Cell Biology
Background:
- Mononuclear phagocytes exhibit increased activity upon stimulation with bacterial lipopolysaccharide (LPS), phorbol myristate acetate (PMA), or muramyl dipeptide (MDP).
- These stimuli are known to enhance phagocytosis, oxidative metabolism, monokine secretion, and cytotoxicity.
Purpose of the Study:
- To investigate the expression of a novel plasma membrane antigen, Mo3e, on human peripheral blood monocytes following stimulation.
- To determine if Mo3e expression can serve as a marker for monocyte activation.
Main Methods:
- Human peripheral blood monocytes were cultured with LPS, PMA, or MDP.
- Mo3e expression was assessed using immunofluorescence flow cytometry and a murine monoclonal antibody.
- The role of LPS's lipid A component was investigated using polymyxin B.
- The effect of protein synthesis inhibitors and temperature on Mo3e acquisition was examined.
- Monocytic cell line U-937 was used to confirm findings.
Main Results:
- LPS, PMA, and MDP induced significant expression of the Mo3e antigen on monocytes.
- Mo3e expression was dose-dependent and required protein synthesis.
- Polymyxin B inhibited LPS-induced Mo3e expression, indicating the lipid A component's role.
- Interferon-gamma (IFN-γ) did not induce Mo3e expression, although it enhanced Ia antigen expression.
- LPS and PMA also induced Mo3e expression in the U-937 monocytic cell line.
Conclusions:
- Mo3e is a novel plasma membrane antigen acquired by human monocytes upon stimulation with LPS, PMA, or MDP.
- Mo3e expression represents a potential immunologic marker for in vitro monocyte activation by these specific stimuli.
