The Maxpar Human Helper T Cell Phenotyping Panel Kit is for the identification and phenotyping of human CD4+ helper T cell subsets, including T helper 1 (Th1), Th2, Th17, Th22, T follicular helper (TFH) and T regulatory (Treg). Differentiation of CD4+ T cells into functionally distinct helper T subsets is essential for normal immunoregulation. These subsets are specified by extrinsic and intrinsic cues, and the resultant cell populations acquire stable phenotypes defined by expression of signature cytokines, master regulator transcription factors, and characteristic cell surface phenotypes. Originally, CD4+ T cells were viewed as having only 2 major fates: T helper 1 (Th1) cells, which express T-bet and selectively produce interferon IFNγ, and Th2 cells, which express GATA3 and produce interleukin IL-4. Although this represented a simple model system for understanding basic principals in cellular immunology, the Th1/Th2 paradigm failed to explain several facets of immunity and autoimmunity. The recognition of cells that selectively produce IL-17 and the transcription factor RORγt (Th17 cells) led to renewed interest in the topic of helper T cell differentiation. Treg cells are another CD4+ lineage with essential immunosuppressive functions that express the master transcription factor Foxp3. Newer fates for helper T cells, including Th22 cells, continue to be identified, with nomenclature based on production of their signature cytokines. The newest lineage of CD4 T cells, follicular helper T (TFH) cells, are crucial for providing B cell help by promoting class-switching of B cells. They are defined by expression of master regulator Bcl-6 and effector cytokine IL-21, along with key surface molecules (PD-1, CXCR5, and ICOS).