Cell-mediated immunity

Definition

Cell-mediated immunity is a crucial aspect of the adaptive immune response that primarily involves T lymphocytes, or T cells, in recognizing and responding to infected or abnormal cells. This type of immunity is essential for targeting intracellular pathogens like viruses and certain bacteria, as well as cancerous cells, ensuring that the immune system effectively eliminates threats from within the body's own cells. T cells play various roles in this process, including direct killing of infected cells and helping to orchestrate other immune responses.

5 Must Know Facts For Your Next Test

1. Cell-mediated immunity is particularly important for fighting off viral infections and controlling tumors by recognizing altered or infected self-cells.
2. Cytotoxic T cells are activated when they recognize foreign antigens presented by Major Histocompatibility Complex (MHC) molecules on the surface of infected cells.
3. Helper T cells play a key role in amplifying the immune response by activating B cells and enhancing the function of cytotoxic T cells.
4. Memory T cells are formed after an initial infection and provide long-lasting immunity by quickly responding to previously encountered pathogens.
5. Dysregulation of cell-mediated immunity can lead to autoimmune diseases, where the immune system mistakenly attacks the body's own healthy cells.

Review Questions

• How do T lymphocytes contribute to cell-mediated immunity, and what are their different functional types?
  • T lymphocytes are essential components of cell-mediated immunity, with two main functional types: cytotoxic T cells and helper T cells. Cytotoxic T cells directly target and destroy infected or cancerous cells by recognizing specific antigens presented on MHC molecules. Helper T cells support other immune functions by releasing cytokines that stimulate B cells and enhance the activity of cytotoxic T cells, thereby coordinating a robust immune response against pathogens.
• Discuss the mechanisms through which cytotoxic T cells eliminate infected or abnormal cells during cell-mediated immunity.
  • Cytotoxic T cells eliminate infected or abnormal cells primarily through two mechanisms: the release of perforin and granzymes, and the engagement of death receptors. When a cytotoxic T cell recognizes an infected cell via specific antigen-MHC interactions, it releases perforin that forms pores in the target cell's membrane. This allows granzymes to enter the cell, triggering apoptosis. Additionally, cytotoxic T cells can bind to death receptors on target cells, inducing programmed cell death through receptor-mediated pathways.
• Evaluate the impact of memory T cells on long-term immunity in relation to cell-mediated immunity.
  • Memory T cells have a significant impact on long-term immunity as they provide a rapid and effective response upon re-exposure to previously encountered pathogens. Following an initial infection, some activated T lymphocytes differentiate into memory T cells that persist in the body for years. If the same pathogen infects the host again, these memory T cells can quickly recognize the antigen and initiate a robust immune response much faster than during the primary exposure. This mechanism is crucial for developing effective vaccines and offers protection against future infections.

Related terms

T lymphocytes:

A type of white blood cell that plays a central role in cell-mediated immunity, with subtypes including cytotoxic T cells and helper T cells.

Cytotoxic T cells:

A subtype of T lymphocyte that directly kills infected or cancerous cells by recognizing specific antigens presented on their surfaces.

Helper T cells: A subtype of T lymphocyte that aids other immune cells by releasing signaling molecules called cytokines, enhancing the overall immune response.