2.5.6 The Role of Helper T cells

Key Roles of Helper T Cells:

1. Activation of Helper T Cells:

• Antigen-presenting cells (APCs), such as macrophages or dendritic cells, present non-self antigens bound to MHC class II molecules to helper T cells.
• The T cell receptor (TCR) on the helper T cell binds to the antigen-MHC complex, activating the Tᕼ cell.
• Once activated, helper T cells divide by clonal expansion and release cytokines to stimulate other immune cells.

2. Stimulating Other Immune Cells:

• B Cells:
• Helper T cells release cytokines (e.g., interleukins) to stimulate B cells to divide and differentiate into plasma cells (which produce antibodies) and memory B cells.
• Cytotoxic T Cells (Tᴄ):
• Helper T cells enhance the activation and proliferation of cytotoxic T cells, which kill infected or abnormal cells by releasing perforins and granzymes.
• Phagocytes:
• Helper T cells secrete cytokines to recruit macrophages and neutrophils, increasing the efficiency of phagocytosis.

3. Coordinating the Immune Response:

• Helper T cells act as immune system regulators, ensuring a targeted and effective response by activating the appropriate cells.
• Without helper T cells, the immune response is weakened or absent (e.g., in HIV/AIDS).

The Importance of Helper T Cells:

1. Link Between Innate and Adaptive Immunity:

• Helper T cells respond to APCs and activate other immune cells, bridging the innate and adaptive immune responses.

2. Immunological Memory:

• Helper T cells stimulate the formation of memory B cells and memory T cells, enabling faster responses to future infections.

3. Protection Against Pathogens:

• Helper T cells are essential for combating viruses, bacteria, fungi, and other pathogens by coordinating the immune attack.

Diseases Related to Helper T Cell Dysfunction:

4. HIV/AIDS:

• HIV targets CD4 receptors on helper T cells, reducing their numbers and impairing the immune response.
• This leads to increased susceptibility to opportunistic infections.

5. Autoimmune Diseases:

• Overactive or misdirected helper T cells can contribute to conditions such as type 1 diabetes or multiple sclerosis.