This study investigates the phenotypic and functional features of human Th17 cells, particularly in the context of Crohn's disease (CD). Th17 cells are a subset of CD4+ T cells that play a protective role against extracellular microbes but are associated with autoimmune disorders in mice. The study demonstrates the presence of Th17 cells in the gut of CD patients, some of which also produce IFN-γ (Th17/Th1). These cells express markers such as IL-23R, CCR6, and RORγt, and exhibit functional similarities, including the ability to help B cells, low cytotoxicity, and resistance to suppression by regulatory T cells. Interestingly, these cells also express T-bet, a transcription factor typically associated with Th1 cells, and their production of IFN-γ can be induced by IL-12, while IL-23 partially inhibits this effect. The study also shows that Th17 and Th17/Th1 cells share functional and receptor characteristics with Th1 and Th2 cells, suggesting a potential developmental or functional relationship between Th17 and Th1. Th17 cells derived from healthy gut areas and peripheral blood also exhibit similar features, indicating that these cells are not unique to CD. The findings highlight the importance of IL-23 in the survival and maintenance of Th17 cells, rather than their expansion. Additionally, the study reveals that Th17 cells can produce IFN-γ in response to IL-12, suggesting a dynamic interplay between Th17 and Th1 cells. The study provides the first detailed phenotypic and functional characterization of human Th17 cells, identifying IL-23R, CCR6, and RORγt as specific markers. It also describes a new subset of Th17 cells that produce IFN-γ and share features with both Th1 and Th17 cells, which has not been previously reported in mice. These findings suggest that Th17 cells in humans can exhibit functional flexibility and may play a significant role in inflammatory processes. The study underscores the importance of understanding the complex interactions between Th17 and Th1 cells in the context of autoimmune diseases.This study investigates the phenotypic and functional features of human Th17 cells, particularly in the context of Crohn's disease (CD). Th17 cells are a subset of CD4+ T cells that play a protective role against extracellular microbes but are associated with autoimmune disorders in mice. The study demonstrates the presence of Th17 cells in the gut of CD patients, some of which also produce IFN-γ (Th17/Th1). These cells express markers such as IL-23R, CCR6, and RORγt, and exhibit functional similarities, including the ability to help B cells, low cytotoxicity, and resistance to suppression by regulatory T cells. Interestingly, these cells also express T-bet, a transcription factor typically associated with Th1 cells, and their production of IFN-γ can be induced by IL-12, while IL-23 partially inhibits this effect. The study also shows that Th17 and Th17/Th1 cells share functional and receptor characteristics with Th1 and Th2 cells, suggesting a potential developmental or functional relationship between Th17 and Th1. Th17 cells derived from healthy gut areas and peripheral blood also exhibit similar features, indicating that these cells are not unique to CD. The findings highlight the importance of IL-23 in the survival and maintenance of Th17 cells, rather than their expansion. Additionally, the study reveals that Th17 cells can produce IFN-γ in response to IL-12, suggesting a dynamic interplay between Th17 and Th1 cells. The study provides the first detailed phenotypic and functional characterization of human Th17 cells, identifying IL-23R, CCR6, and RORγt as specific markers. It also describes a new subset of Th17 cells that produce IFN-γ and share features with both Th1 and Th17 cells, which has not been previously reported in mice. These findings suggest that Th17 cells in humans can exhibit functional flexibility and may play a significant role in inflammatory processes. The study underscores the importance of understanding the complex interactions between Th17 and Th1 cells in the context of autoimmune diseases.