Definition
Cellular immunity involves T lymphocytes (T cells) that target infected cells, tumor cells, or intracellular pathogens.
Unlike humoral immunity, it does not rely on antibodies but instead directly attacks infected or abnormal cells.
Key Players
T lymphocytes (T cells) – Produced in the bone marrow, mature in the thymus.
T-helper cells (CD4⁺ cells) – Regulate immune responses via cytokines.
Cytotoxic T cells (CD8⁺ cells) – Directly kill infected or abnormal cells.
Memory T cells – Provide long-term immunity.
Mechanism of Cellular Immunity
1) Antigen Recognition
T cells recognize antigen fragments presented on MHC molecules on infected or abnormal cells.
2) Types of T Cells Involved
A) CD8⁺ Cytotoxic T Cells (CTLs)
Recognize antigens presented on MHC-I.
Kill infected or cancerous cells using:
Perforins – Create pores in target cells.
Granzymes – Induce apoptosis (cell death).
B) CD4⁺ Helper T Cells (Th Cells)
Recognize antigens presented on MHC-II by antigen-presenting cells (APCs).
Secrete cytokines that:
Activate macrophages for enhanced pathogen destruction.
Promote inflammation.
Enhance B cell antibody production.
Assist CD8⁺ T cells in activation.
Advantages of Cellular Immunity
Eliminates intracellular infections (e.g., viruses, intracellular bacteria, protozoa).
Essential for tumor surveillance, preventing cancer growth.
Orchestrates the immune response, supporting antibody production and immune regulation.
