Medicine & USMLE

Th1 Cells

B Cells and T Cells
  1. MHC I
  2. MHC II
  3. B Cells - Overview
  4. B Cells - Activation
  5. Plasma B Cells
  6. Memory B Cells
  7. T Cells - Overview
  8. T Cells - Activation
  9. T Cells - Differentation
  10. Cytotoxic (Killer) T Cells
  11. Helper T Cells - Overview
  12. Th1 Cells
  13. Th2 Cells
  14. Th17 Cells
  15. Regulatory T Cells (Tregs)


T-Helper Type 1 (Th1) cells are a subset of effector helper T-cells that coordinate attacks against intracellular pathogens. Th1 cell differentiation is stimulated by interleukin-12 (IL-12), a cytokine produced by macrophages. Once Th1 cells are formed, they secrete two products: interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). IL-2 stimulates Killer T-cells and NK cells, which go on to directly kill infected cells. However, IL-2 also works in an autocrine fashion to stimulate proliferation of Helper T-Cells, which eventually increases the number of Th1 cells, amplifying the immune response. On the other hand, IFN-gamma activates macrophages. These activated macrophages increase their antigen presenting roles and release of IL-12, which goes back to stimulate Th1 cells. This feedback loop between macrophages and Th1 ensures a robust immune response against intracellular pathogens.

Key Points

  • T Helper Type 1 (Th1) Cell
    • Subset of effector (activated) Helper T-cells
    • Generally coordinate immune response against intracellular antigens
    • Induced by Interleukin-2 (IL-2), Interleukin-12 (IL-12)
      • IL-2 also produced by Th1, works in an autocrine fashion
      • IL-12 from macrophages binds to IL-12R to induce differentiation of Th1 cells; defective signalling in IL-12R Deficiency
      • All Th-cell types are cross-inhibitory, so Th1 differentiation is inhibited by IL-4 and IL-10 (cytokines mediating Th2 line)
    • Secretes Interferon gamma (IFN-gamma), and IL-2
      • IL-2 stimulates Killer T-cells and NK cells
      • IFN-gamma activates Macrophages to kill microbes
        • Macrophages also involved in granuloma formation, so Th1 signalling is involved in pathophysiology of granulomas