Cell-mediated immunity

Definition

Cell-mediated immunity is a crucial aspect of the adaptive immune response that involves the activation of T cells to recognize and eliminate infected or cancerous cells. This process does not rely on antibodies but instead depends on the direct actions of T lymphocytes, particularly cytotoxic T cells and helper T cells, to coordinate the immune response. It plays a key role in controlling intracellular pathogens, such as viruses and certain bacteria, and is essential for graft rejection and tumor surveillance.

5 Must Know Facts For Your Next Test

1. Cell-mediated immunity is primarily mediated by T cells, which can directly kill infected or cancerous cells without the involvement of antibodies.
2. Cytotoxic T cells (CD8+ T cells) are specifically responsible for recognizing and destroying virus-infected cells by inducing apoptosis.
3. Helper T cells (CD4+ T cells) are crucial in orchestrating the immune response by releasing cytokines that enhance the activity of other immune cells, including B cells and macrophages.
4. Antigen presentation is essential for activating T cells; this occurs when dendritic cells or other antigen-presenting cells present processed antigens to T cell receptors.
5. Cell-mediated immunity is particularly important in responding to intracellular pathogens and in situations like organ transplantation, where it can contribute to graft rejection.

Review Questions

• How do cytotoxic T cells contribute to cell-mediated immunity, and what mechanisms do they use to eliminate infected cells?
  • Cytotoxic T cells contribute to cell-mediated immunity by specifically recognizing infected or cancerous cells through their T cell receptors, which bind to antigens presented by major histocompatibility complex (MHC) molecules on the surface of these target cells. Once activated, cytotoxic T cells release perforin and granzymes, which form pores in the target cell's membrane and induce apoptosis. This direct killing mechanism allows them to effectively eliminate intracellular pathogens and maintain cellular integrity.
• Discuss the role of helper T cells in cell-mediated immunity and how they interact with other components of the immune system.
  • Helper T cells play a pivotal role in cell-mediated immunity by providing essential signals that activate both cytotoxic T cells and B cells. They recognize antigens presented by antigen-presenting cells through MHC class II molecules. Upon activation, helper T cells secrete cytokines that enhance the proliferation and differentiation of cytotoxic T cells and stimulate other immune components like macrophages to improve their pathogen-fighting abilities. This coordination ensures a robust immune response against infections.
• Evaluate the importance of antigen presentation in the activation of T cells during cell-mediated immunity and its implications for immune response effectiveness.
  • Antigen presentation is fundamental for the activation of T cells in cell-mediated immunity because it bridges the recognition of pathogens with the initiation of an immune response. Antigen-presenting cells process foreign antigens and display them on their surface using MHC molecules, allowing naive T cells to recognize specific antigens. This critical interaction ensures that only those T cells that can respond to specific threats are activated. The effectiveness of the immune response relies on this precise mechanism, as improper antigen presentation can lead to insufficient responses against infections or autoimmunity if self-antigens are mistakenly recognized.

Related terms

T lymphocytes: A type of white blood cell that plays a central role in cell-mediated immunity, including cytotoxic T cells that kill infected cells and helper T cells that assist other immune cells.

Antigen presentation: The process by which antigen-presenting cells display foreign antigens on their surface to activate T cells, which is vital for initiating cell-mediated immunity.

Cytokines:

Signaling molecules released by immune cells that mediate and regulate immunity, inflammation, and hematopoiesis, playing a significant role in coordinating the immune response during cell-mediated immunity.