Medicine & USMLE

Helper T Cells - Overview

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)


Helper T-cells are a type of T-cells in the adaptive immune system that work by coordinating the actions of other immune cells against a specific antigen. Specifically, they use chemical signals called cytokines to tell other cells what to do in response to a threat. Helper T-cells are identified by their expression of CD4, which distinguishes them from other types of T-cells. This CD4 is also responsible for recognizing MHC II, an antigen-presenting complex found exclusively on antigen-presenting cells (APC). Once activated to a threat (specific antigen), helper T-cells then differentiate into effector subtypes (including Th1, Th2, and Th17), depending on the type of antigen presented. The effector subtype determines what cytokines the active Helper T-cell will eventually produce.

Key Points

  • Helper T Cells (Th Cells)
    • Subtype of T-lymphocytes in the adaptive immune system
    • Express CD4 (also known as CD4+ T-cells)
    • Recognize antigens bound to MHC II
      • Via T-cell receptors (TCR) with the help of CD4
    • Stimulated by Interleukin-2 (IL-2)
      • IL-2 stimulates growth of all lymphocytes, including T-cells
    • After T-cell Activation, differentiate into effector subtypes depending on antigen presented:
    • Primary target in HIV infection