Immunosuppressive Effect of Mesenchymal Stromal Cells is Enhanced by IL-1α from Oral Squamous Cell Carcinoma Cells

Background: We have already reported that mouse Oral Squamous Carcinoma Cells (OSCCs) Sq-1979 specifically enhance the immunosuppressive activity of mesenchymal 10T1/2 cells via the functional soluble factor (s). Objective: In this report, we attempted to identify soluble factor(s) mediating the immunosuppression of Sq-1979 cells. Methods: L5-11 cells are a variant established from the metastatic lymph nodes of Sq-1979-implanted mice. Unlike parental Sq-1979 cells, however, L5-11 cells lack promotion of immunosuppressive activity in 10T1/2 cells. In order to identify cytokine mRNAs specifically expressed in Sq-1979 cells but not in L5-11 cells, eDNA microarray was performed. Conditioned medium from Sq-1979 cells (CM) was absorbed by several different neutralizing antibodies (abs) against the corresponding cytokines. The absorbed CM was then co-cultured with 10T1/2 cells and anti-CD3 antibody-stimulated mouse spleen cells. The Interferon (IFN)gamma-producing capability of the stimulated spleen cells was evaluated using Enzyme-Linked Immunosorbent Assay (ELISA). By using a specific cytokine product instead of CM in this co-culture system the source of the immunosuppressive effect was identified. Results: The expression of Ccl2, Ccl7, Il1-alpha, IL1f6 and Il6 mRNAs was specifically elevated in Sq-1979 cells compared to L5-11 cells. The suppression of the IFN-gamma producing capability of stimulated spleen cells in the co-culture system was specifically alleviated by absorbing the CM with anti-IL-1 alpha ab. We further demonstrated that the immunosuppressive effect of CM in the co-culture system could be completely substituted by IL-1 alpha protein (50 pmol/ml). Conclusion: The immunosuppressive function of 10T1/2 cells is specifically promoted by IL-1 alpha, secreted by Sq-1979 cells.