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Interferon-gamma and interleukin-4 down-regulate soluble CD14 release in human monocytes and macrophages
R Landmann1, A E Fisscher, J P Obrecht
1Department of Research, University Hospital, Basel, Switzerland.
Abstract:
CD14 is a 53-kd glycoprotein that is mainly expressed in myeloid cells and exists in two forms. The membrane-bound form represents the receptor for complexes of lipopolysaccharide (LPS) with LPS binding protein. The function and regulation of the soluble form are unknown. In the present study we investigated the release of soluble CD14 (sCD14) in cultures of human mononuclear leukocytes, elutriated monocytes, and monocyte-derived macrophages. The release of sCD14 into the medium of the cells cultured for 15 and 45 h was investigated in the absence or presence of selected cytokines. sCD14 release occurred constitutively and correlated with cell number. In monocytes differentiating into macrophages, cumulative release of sCD14 was linear from day 1 to day 7. Spontaneous sCD14 release after 15 h of culture (2 x 10(6) cells/ml) was higher in the supernatant from monocytes (314 +/- 58 ng/ml) than that from mononuclear leukocytes (68 +/- 10 ng/ml) and similar to that from macrophages (469 +/- 79 ng/ml). Cycloheximide and actinomycin D inhibited sCD14 release. Recombinant interferon-gamma (rIFN-gamma) and recombinant interleukin-4 (rIL-4) directly decreased sCD14 release in mononuclear leukocyte, monocyte, and macrophage cultures. rIL-2 and rIFN-alpha reduced sCD14 release into the supernatants of mononuclear leukocytes only. Use of anti-IFN-gamma antibodies indicated that the down-regulation of sCD14 release by rIL-2 and rIFN-alpha was partially due to induction of endogenous IFN-gamma. The down-regulation of sCD14 release by all four cytokines was both time and dose dependent. rIFN-gamma and rIL-4 added simultaneously had a synergistic effect on sCD14 down-regulation. In conclusion, sCD14 release may have an immunomodulatory role in circulating monocytes, is apparently not related to the process of macrophage differentiation, and is selectively down-regulated during an immune response when levels of IFN-gamma and IL-4 are high.
Insights
Soluble CD14 (sCD14) is released constitutively by myeloid cells. Cytokines like interferon-gamma and interleukin-4 selectively decrease sCD14 release, suggesting an immunomodulatory role during immune responses.
Area of Science:
- Immunology
- Cell Biology
Background:
- CD14 is a glycoprotein primarily on myeloid cells, existing in membrane-bound and soluble forms.
- The function and regulation of soluble CD14 (sCD14) are largely unknown.
- sCD14 is involved in lipopolysaccharide (LPS) recognition via its membrane-bound form.
Purpose of the Study:
- To investigate the release of soluble CD14 (sCD14) from human myeloid cells.
- To determine the effect of cytokines on sCD14 release.
- To explore the potential immunomodulatory role of sCD14.
Main Methods:
- Culturing human mononuclear leukocytes, monocytes, and macrophages.
- Measuring sCD14 release in cell supernatants over time.
- Treating cultures with cytokines (IFN-γ, IL-4, IL-2, IFN-α) and inhibitors (cycloheximide, actinomycin D).
Main Results:
- sCD14 was constitutively released by all tested myeloid cell types, correlating with cell number.
- Monocytes and macrophages released significantly more sCD14 than mononuclear leukocytes.
- Interferon-gamma (IFN-γ) and Interleukin-4 (IL-4) dose- and time-dependently decreased sCD14 release, with a synergistic effect when combined.
- Interleukin-2 (IL-2) and Interferon-alpha (IFN-α) also reduced sCD14 release, partly via endogenous IFN-γ induction.
Conclusions:
- sCD14 release is constitutive and not directly tied to macrophage differentiation.
- Cytokine-mediated down-regulation of sCD14 suggests a role in modulating immune responses.
- High levels of IFN-γ and IL-4 during immune responses may selectively reduce sCD14 levels.