Th2

Th2 cells, or T helper type 2 cells, are a subset of CD4+ T lymphocytes that coordinate humoral immunity and defense against extracellular parasites. They differentiate from naive CD4+ T cells in response to IL-4 signaling, with the transcription factor GATA3 acting as a master regulator. IL-4, produced by developing Th2 cells and by mast cells and basophils, supports the Th2 differentiation and can inhibit Th1 development.

The cytokine profile of Th2 cells is characteristic and includes IL-4, IL-5, and IL-13, with occasional IL-9 production by some cells. IL-4 and IL-13 promote B cell isotype switching toward IgE, a key feature of allergic responses, while IL-5 drives eosinophil growth, recruitment, and activation. IL-13 shares several functions with IL-4, contributing to mucus production and airway hyperresponsiveness.

Functions of Th2 cells center on helping B cells produce antibodies and promoting immune responses at mucosal surfaces. They also participate in defense against helminth infections by mediating eosinophil and cytokine responses. Th2 activity can be antagonistic to Th1 and Th17 pathways, influencing the overall balance of cellular versus humoral immunity.

Regulation of Th2 responses involves complex networks of cytokines and regulatory cells, and skewing toward Th2 can contribute to allergic diseases such as asthma, atopic dermatitis, and allergic rhinitis. Conversely, Th2 responses can be beneficial for parasite control where appropriate.

Clinical relevance includes therapies targeting Th2-associated pathways. For example, blockade of IL-4 and IL-13 signaling by IL-4 receptor alpha inhibitors, and anti-IL-5 or anti-IL-5 receptor therapies, are used to reduce eosinophilic inflammation in allergic diseases. Th2 biology remains a focus of research due to its central role in allergy and parasitic defense.