CD11b+Ly6C++Ly6G- cells show distinct function in mice with chronic inflammation or tumor burden

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>S100A9 has been shown to be important for the function of so called Myeloid Derived Suppressor Cells (MDSC). Cells with a similar phenotype are also involved in pro-inflammatory processes, and we therefore wanted to investigate the gene expression and function of these cells in animals that were either subjected to chronic inflammation, or inoculated with tumors.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>CD11b<jats:sup>+</jats:sup>Ly6C<jats:sup>++</jats:sup>and Ly6G<jats:sup>+</jats:sup>cells were isolated from spleen, tumor tissue or inflammatory granulomas. S100A9, Arginase 1 and iNOS gene expression in the various CD11b<jats:sup>+</jats:sup>cell populations was analyzed using Q-PCR. The suppressive activity of the CD11b<jats:sup>+</jats:sup>cell populations from different donors was studied in co-culture experiments.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>S100A9 was shown to be expressed mainly in splenic CD11b<jats:sup>+</jats:sup>Ly6C<jats:sup>+</jats:sup>G<jats:sup>+</jats:sup>cells both at the RNA and protein level. Arginase I and iNOS expression could be detected in both CD11b<jats:sup>+</jats:sup>Ly6C<jats:sup>+</jats:sup>Ly6G<jats:sup>+</jats:sup>and CD11b<jats:sup>+</jats:sup>Ly6C<jats:sup>+</jats:sup>G<jats:sup>-</jats:sup>/C<jats:sup>++</jats:sup>G<jats:sup>-</jats:sup>derived from tumors or a site of chronic inflammation, but was very low in the same cell populations isolated from the spleen. CD11b<jats:sup>+</jats:sup>cells isolated from mice with peritoneal chronic inflammation were able to stimulate T lymphocytes, while CD11b<jats:sup>+</jats:sup>cells from mice with peritoneal tumors suppressed T cell growth.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>An identical CD11b<jats:sup>+</jats:sup>Ly6C<jats:sup>++</jats:sup>G<jats:sup>-</jats:sup>cell population appears to have the ability to adopt immune stimulatory or immune suppressive functions dependent on the presence of a local inflammatory or tumor microenvironment. Thus, there is a functional plasticity in the CD11b<jats:sup>+</jats:sup>Ly6C<jats:sup>++</jats:sup>G<jats:sup>-</jats:sup>cell population that cannot be distinguished with the current molecular markers.</jats:p></jats:sec>