Th1

Th1 cells, or T helper type 1 cells, are a subset of CD4+ T lymphocytes that support cell-mediated immune responses. They differentiate from naive CD4+ T cells in the presence of interleukin-12 (IL-12) and interferon-γ (IFN-γ) signaling, with the transcription factor T-bet driving their development and function. Th1 cells predominantly produce IFN-γ, as well as interleukin-2 (IL-2) and tumor necrosis factor-α (TNF-α).

The principal role of Th1 cells is to activate macrophages and promote intracellular immunity, helping control pathogens such as viruses and intracellular bacteria. IFN-γ produced by Th1 cells enhances antigen presentation and supports the activation of cytotoxic T cells, contributing to effective cell-mediated defense.

Th1 responses are part of the broader Th1/Th2 paradigm and are regulated by the cytokine milieu. Th2 cytokines, notably IL-4, can suppress Th1 differentiation, while regulatory mechanisms, including IL-10 and transforming growth factor-β (TGF-β), can dampen Th1 activity. Th1 responses can also contribute to granulomatous inflammation and are implicated in certain autoimmune and inflammatory conditions when dysregulated.

Clinical relevance lies in how skewing toward a Th1 profile influences infection outcomes and autoimmune disease risk. Therapeutic approaches that modulate IL-12, IFN-γ, or T-bet activity can alter Th1 differentiation and effector function.