cell mediated - Histology

Cell-mediated immunity is a crucial component of the adaptive immune system, primarily involving the activation and response of T cells. Unlike humoral immunity, which relies on antibodies produced by B cells, cell-mediated immunity does not involve antibodies. Instead, it focuses on the direct destruction of infected or abnormal cells by T cells.

Key Players in Cell-Mediated Immunity

The main cells involved in cell-mediated immunity are:

- T lymphocytes (T cells): These are the primary effectors of cell-mediated immunity. They are produced in the bone marrow and mature in the thymus.
- Antigen-presenting cells (APCs): These cells, such as dendritic cells and macrophages, present antigens to T cells, initiating the immune response.
- Cytotoxic T cells (CTLs): These T cells directly kill infected or cancerous cells.
- Helper T cells (Th cells): These cells assist other immune cells by releasing cytokines that help regulate the immune response.

Mechanism of Action

The process of cell-mediated immunity involves several key steps:

1. Antigen Presentation: APCs capture antigens from pathogens and present them on their surface using major histocompatibility complex (MHC) molecules.
2. T Cell Activation: When a T cell receptor (TCR) on a T cell recognizes and binds to the antigen-MHC complex, the T cell becomes activated.
3. Clonal Expansion: Activated T cells proliferate and differentiate into various subtypes, including helper T cells and cytotoxic T cells.
4. Target Cell Destruction: Cytotoxic T cells recognize infected or abnormal cells presenting the antigen and release perforin and granzymes, leading to the target cell’s apoptosis.

Types of T Cells Involved

There are multiple subtypes of T cells involved in cell-mediated immunity:

- Helper T cells (CD4+ T cells): These cells are critical for orchestrating the immune response by releasing cytokines that activate other immune cells.
- Cytotoxic T cells (CD8+ T cells): They are responsible for directly killing infected, cancerous, or damaged cells.
- Regulatory T cells (Tregs): These cells help maintain immune tolerance and prevent autoimmune responses.

Role of Cytokines

Cytokines are signaling molecules that play a pivotal role in the immune response. Helper T cells release various cytokines, such as interleukin-2 (IL-2), which promotes T cell proliferation, and interferon-gamma (IFN-γ), which activates macrophages and enhances their pathogen-killing abilities.

Clinical Relevance

Understanding cell-mediated immunity has significant clinical implications:

- Immunotherapy: Techniques that enhance the cell-mediated immune response, such as CAR-T cell therapy, are used to treat cancers.
- Transplantation: Cell-mediated immunity is a critical factor in transplant rejection, where the recipient’s T cells attack the transplanted organ.
- Autoimmune Diseases: Dysregulation of cell-mediated immunity can lead to autoimmune conditions, where the immune system mistakenly targets the body’s own cells.

Conclusion

Cell-mediated immunity is a vital aspect of the immune system, involving the intricate interplay of various cells and molecules to protect the body from infections and malignancies. Understanding its mechanisms and roles paves the way for advancements in medical treatments and therapies.