- T helper 2 (Th2) cells are a distinct subset of CD4+ T lymphocytes that play a crucial role in humoral immunity and host defense against extracellular pathogens, particularly parasitic worms (helminths) and other multicellular organisms. These cells are essential mediators of allergic responses and contribute to mucosal immunity.
- The differentiation of Th2 cells from naïve CD4+ T cells is primarily driven by interleukin-4 (IL-4), which can be initially produced by various cell types including basophils, mast cells, and innate lymphoid cells. The transcription factor GATA3 serves as the master regulator of Th2 cell development and function. Once differentiated, Th2 cells produce their characteristic array of cytokines, including IL-4, IL-5, IL-9, IL-13, and IL-25, each serving distinct but complementary functions in the immune response.
- These signature cytokines orchestrate a complex immune response aimed at eliminating extracellular pathogens. IL-4 promotes B cell class switching to produce IgE antibodies and further drives Th2 cell differentiation in a positive feedback loop. IL-5 stimulates the production, activation, and recruitment of eosinophils, while IL-13 induces mucus production by goblet cells and promotes smooth muscle contractility in the airways. Together, these responses create an environment hostile to parasitic invaders.
- Th2 cells coordinate multiple aspects of the immune response through their interactions with other immune cells. They support B cell differentiation and antibody production, particularly IgE synthesis, which is crucial for allergic responses and anti-parasitic immunity. They also activate and recruit eosinophils, stimulate mucus production, and enhance smooth muscle contractility in the airways. Additionally, Th2 responses promote tissue repair and can help restore homeostasis following inflammation or injury.
- While Th2 responses are essential for protection against certain pathogens, dysregulation of Th2 immunity is associated with various pathological conditions. Excessive or inappropriate Th2 responses are central to the development of allergic diseases such as asthma, atopic dermatitis, and allergic rhinitis. The IgE-mediated hypersensitivity reactions orchestrated by Th2 cells can lead to acute allergic responses and chronic inflammatory conditions. Therefore, like other T helper subsets, Th2 cell responses must be carefully regulated to maintain immune homeostasis and prevent allergic disease.
- Understanding the role of Th2 cells in both protective immunity and pathological conditions is crucial for developing targeted therapies for allergic diseases and parasitic infections. The balance between Th2 and other T helper cell responses, particularly Th1 responses, is critical for appropriate immune function and health maintenance.
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