Tumor Growth Alters T Cell and Macrophage Production of and Responsiveness to Granulocyte-Macrophage Colony-Stimulating Factor: Partial Dysregulation through Interleukin-10

Tumor growth induces phenotypic and functional changes among splenic T cells and macrophages (Mφ) that contribute to the immunosuppression observed in tumor-bearing hosts (TBH). These changes partly arise through alterations in immune cell production of and responsiveness to cytokines. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important T cell- and Mφ-derived cytokine that is produced during normal host immunogenic challenge, but itʹs involvement during cancer is poorly defined. In contrast, interleukin-10 (IL-10) is an inhibitory cytokine that is produced by immune cells as a deactivation factor. IL-10 can disrupt GM-CSF synthesis and may be associated with tumor-induced changes in cytokine synthesis. We determined if tumor growth alters T-cell and Mφ synthesis of and responsiveness to GM-CSF, and if these alterations occur because tumor growth heightens immune cell sensitivity to IL-10. Tumor growth significantly decreased T-cell synthesis of GM-CSF during activation by concanavalin A, and TBH T cells were more susceptible to GM-CSF synthesis inhibition by IL-10 than their normal host (NH) counterparts. This suppression was observed using both unseparated splenic lymphocyte preparations and purified CD4+ and CD8+ T cells. Similarly, TBH Mφ (both splenic and peritoneal) produced less GM-CSF than NH Mφ during activation by lipopolysaccharide. Tumor growth also altered major histocompatibility complex (MHC) class II- Mφ GM-CSF synthesis. TBH Mφ were more susceptible to GM-CSF synthesis inhibition by IL-10 than their NH counterparts. Although TBH T cells demonstrate less proliferation than NH T cells during activation, tumor growth did not compromise T-cell responsiveness to GM-CSF. However, tumor growth did increase TBH T-cell susceptibility to inhibition of proliferation by IL-10. Tumor growth suppressed Mφ responsiveness to GM-CSF, and IL-10 further decreased Mφ responsiveness to GM-CSF. Collectively, these results suggest that T cell and Mφ production of and responsiveness to GM-CSF is disrupted during tumor growth, and that TBH T cells and Mφ are more susceptible to the suppressor activity of IL-10 than their NH counterparts.