CD4 T cells, also known as helper T cells, orchestrate the immune system's response to infections and diseases. They don't directly kill infected cells, but instead, they activate and coordinate other immune cells to do so.
Key Functions of CD4 T Cells:
-
Activation of B cells: CD4 T cells help B cells mature and produce antibodies, which neutralize pathogens and mark them for destruction. This involves direct contact and the release of specific cytokines.
-
Activation of Cytotoxic T Cells (CD8 T cells): They assist in the activation and proliferation of cytotoxic T cells, which directly kill infected or cancerous cells. Again, this is facilitated through cytokine release and direct interaction.
-
Activation of Macrophages: CD4 T cells activate macrophages, enhancing their ability to engulf and destroy pathogens (phagocytosis) and present antigens to other immune cells.
-
Cytokine Production: Perhaps their most crucial function, CD4 T cells secrete various cytokines, which are signaling molecules that influence the behavior of other immune cells. Different types of CD4 T cells produce different cytokines, allowing for a tailored immune response. Examples of CD4 T cell subsets include:
- Th1 cells: Produce IFN-γ, which activates macrophages and promotes cell-mediated immunity against intracellular pathogens.
- Th2 cells: Produce IL-4, IL-5, and IL-13, which stimulate B cell antibody production, particularly IgE, and promote immunity against parasites and allergens.
- Th17 cells: Produce IL-17, which recruits neutrophils and promotes inflammation, important for fighting extracellular bacteria and fungi.
- Treg cells: Produce IL-10 and TGF-β, which suppress the immune response and prevent autoimmunity.
-
Antigen Presentation: While not their primary function, CD4 T cells also interact with antigen-presenting cells (APCs) like dendritic cells, which present processed antigens bound to MHC class II molecules. This interaction is critical for initiating the adaptive immune response.
In summary, CD4 T cells are central to adaptive immunity, acting as coordinators and regulators that fine-tune the immune response to effectively combat a wide range of threats. Their role in activating other immune cells and producing cytokines makes them essential for a robust and targeted immune defense.
