Production of Lymphocytes - Cellular Immune Response (Response of T-Cells to Antigens)

Cell-mediated immunity operates through a sequential activation cascade rather than a single-step reaction. Understanding this sequence is essential for diagram-based board questions.

1. Antigen Recognition: A specific antigen enters the body and is recognised by a matching T-cell.
2. Cloning: The T-cell clones itself; each clone remains specific to a single antigen.
3. Migration: Programmed T lymphocytes travel to lymphoid tissue (spleen, lymph nodes).
4. Transformation: These cells transform into lymphoblasts within the lymphoid tissue.
5. Division: Lymphoblasts divide repeatedly to produce activated T-lymphocytes.
6. Site Migration: Activated T-lymphocytes migrate to the site of antigen entry to carry out their specific function.

There are four major types of T-cells, each with a distinct immunological role.

1. Cytotoxic T-Cells (Killer T-Cells)

• Directly destroy antigen-containing cells
• Primary defense against virus-infected cells
• Release cytotoxic substances that lyse the target cell

2. Helper T-Cells

• Do not attack pathogens directly
• Stimulate B-cells to produce antibodies
• Activate macrophages through lymphokines
• Destroyed by HIV, leading to AIDS (a key exam linkage point)

3. Suppressor T-Cells (Regulatory T-Cells)

• Inhibit and control immune responses
• Prevent overactivity of the immune system
• Maintain immunological tolerance toward self-antigens

4. Memory T-Cells

• Remain dormant in lymphoid tissue after the first exposure
• Recognise the same antigen instantly upon re-exposure
• Enable a faster, stronger secondary immune response