A novel tool to identify the relative contribution of lymphoid cell types that contribute to IL-10 production during the infection with Schistosoma mansoni: The TIGER index

• Flow cytometry data and cell count analysis are combined to the TIGER index (TI).
• TI is a combination of flow cytometry data (GFPpos cells; MFI) and total cell numbers.
• The TI allows unveiling the highest producers of IL-10 during S. mansoni infection.
• In late S. mansoni infection, CD4pos CD25neg cells have the highest TI in spleens.
• Using the TI prevents the requirement of external standards in long-term experiments.

Introduction: Infection with the trematode helminth Schistosoma mansoni affects more than 200 million people worldwide. Infected patients are thought to show a decreased incidence of asthma and autoimmune diseases, which is, among others, considered a result of an increased production of the immunoregulatory cytokine IL-10. However, the location and the type of cell that is responsible for the highest production of IL-10 in vivo are still unknown. Aim: Identification of the hierarchy of IL-10 producing cell types in the mesenteric lymph node and spleen during the course of the murine infection with S. mansoni without the need of an external standard. Methods: We describe the use of the IL-10 reporter mouse TIGER for the study of murine schistosomiasis and introduce a novel tool, which we have called the TIGER index (TI). This index combines data from flow cytometric measurements and cell count analysis and allows identifying the cell type with the highest contribution of IL-10 during the course of infection in the secondary lymphoid organs, sites of extensive immunoregulatory activity in schistosomiasis. Results: In this paper we have calculated the TI for the mesenteric lymph nodes and the spleen in the course of a chronic infection with S. mansoni. Using the TI, we identified CD4pos CD25pos and CD4pos CD25neg cell populations as the highest producers of IL-10 in the mesenteric lymph node and the spleen in chronic schistosomiasis, respectively, whereas B cells, NK cells and NKT cells showed a lower contribution to IL-10 production throughout the infection. Conclusion: The TI is a highly useful tool to measure the relative contribution of different cell types, which are responsible for the in vivo production of IL-10 in the secondary lymphoid organs during the infection with S. mansoni. Thus, the strength of the TI ensures the possibility to analyze IL-10 production in a long term experiment without the need of an external standard between each time point of analysis.