CD4+ T cells are crucial for regulated immune responses against pathogens. Naive CD4+ T cells differentiate into various subtypes, such as Th1, Th2, Th17, Treg, Tfh, and Th9, based on cytokine signals and transcription factors. These subtypes have distinct functions, including immune regulation, inflammation, and antibody production. Th1 cells produce IFNγ and are involved in fighting intracellular pathogens, while Th2 cells produce IL4 and are involved in combating extracellular parasites and allergic responses. Th17 cells produce IL17 and are involved in immune responses against bacteria and fungi, while Treg cells suppress immune responses and maintain tolerance. Tfh cells assist B cells in antibody production, and Th9 cells produce IL9 and are associated with allergic diseases. The differentiation of these cells is regulated by complex signaling pathways, transcription factors, and epigenetic modifications. Recent studies have shown that some CD4+ T cell subsets, such as Treg and Th17, exhibit plasticity, allowing them to switch between different functional states. This plasticity has implications for immune diseases and organ transplantation. Understanding the mechanisms of CD4+ T cell differentiation and function is essential for developing therapeutic strategies for immune-related disorders.CD4+ T cells are crucial for regulated immune responses against pathogens. Naive CD4+ T cells differentiate into various subtypes, such as Th1, Th2, Th17, Treg, Tfh, and Th9, based on cytokine signals and transcription factors. These subtypes have distinct functions, including immune regulation, inflammation, and antibody production. Th1 cells produce IFNγ and are involved in fighting intracellular pathogens, while Th2 cells produce IL4 and are involved in combating extracellular parasites and allergic responses. Th17 cells produce IL17 and are involved in immune responses against bacteria and fungi, while Treg cells suppress immune responses and maintain tolerance. Tfh cells assist B cells in antibody production, and Th9 cells produce IL9 and are associated with allergic diseases. The differentiation of these cells is regulated by complex signaling pathways, transcription factors, and epigenetic modifications. Recent studies have shown that some CD4+ T cell subsets, such as Treg and Th17, exhibit plasticity, allowing them to switch between different functional states. This plasticity has implications for immune diseases and organ transplantation. Understanding the mechanisms of CD4+ T cell differentiation and function is essential for developing therapeutic strategies for immune-related disorders.