Which cytokine is primarily produced by TH2 cells?

• A. IFN-γ
• B. IL-4
• C. IL-2
• D. TNF-α

Answer: (B)

TH2 cells specialize in humoral immunity and responses against parasites and allergens. The cytokine they predominantly produce is IL-4, which drives B cells to class-switch to IgE and supports the TH2 differentiation program (via transcription factors like GATA3). This helps explain why TH2 responses are linked to allergic inflammation and antibody-mediated defense. In contrast, IFN-γ is a hallmark of TH1 cells and promotes macrophage activation and cell-mediated immunity. IL-2 is a general T cell growth factor produced by many activated T cells, not specific to TH2, and TNF-α is a broad pro-inflammatory cytokine produced by various cells. Therefore, IL-4 best represents the TH2 cytokine profile.