Cell-mediated response

Definition

The cell-mediated response is a crucial aspect of the adaptive immune system, primarily involving T lymphocytes (T cells) that target and eliminate infected or abnormal cells. This response is vital for combating intracellular pathogens, such as viruses, and plays a significant role in tumor surveillance. T cells recognize specific antigens presented by infected cells or antigen-presenting cells through major histocompatibility complex (MHC) molecules, leading to their activation and subsequent immune action.

5 Must Know Facts For Your Next Test

1. The cell-mediated response is mainly mediated by cytotoxic T cells (CD8+ T cells), which directly kill infected or cancerous cells.
2. Helper T cells (CD4+ T cells) play an important role by releasing cytokines that enhance the activity of other immune cells during the cell-mediated response.
3. The activation of T cells requires two signals: recognition of the antigen-MHC complex and additional co-stimulatory signals from antigen-presenting cells.
4. Once activated, T cells can proliferate and differentiate into memory T cells, providing long-term immunity against previously encountered pathogens.
5. The cell-mediated response is particularly important in controlling infections caused by intracellular pathogens, such as HIV and certain bacteria like Mycobacterium tuberculosis.

Review Questions

• How do T lymphocytes recognize and respond to antigens during the cell-mediated response?
  • T lymphocytes recognize antigens through their T cell receptors (TCRs), which specifically bind to antigen-MHC complexes presented by antigen-presenting cells. The interaction between the TCR and the MHC-peptide complex is critical for the activation of T cells. Additionally, co-stimulatory signals from the antigen-presenting cell are necessary for full activation. Once activated, T cells undergo clonal expansion and differentiation to effectively target and eliminate infected or abnormal cells.
• Discuss the roles of cytotoxic T cells and helper T cells in the cell-mediated response.
  • Cytotoxic T cells (CD8+ T cells) are primarily responsible for directly killing infected or cancerous cells by recognizing specific antigens presented on MHC class I molecules. In contrast, helper T cells (CD4+ T cells) do not directly kill target cells but instead provide essential support by secreting cytokines that enhance the immune response. These cytokines stimulate other immune cells, including B cells and macrophages, facilitating a coordinated attack against pathogens and improving overall immune function.
• Evaluate the importance of the cell-mediated response in combating viral infections compared to humoral immunity.
  • The cell-mediated response is critical for combating viral infections because viruses often replicate inside host cells, where they are not readily accessible to antibodies produced by humoral immunity. Cytotoxic T cells can identify and destroy infected cells displaying viral antigens on their surface via MHC class I molecules. This direct elimination prevents further viral replication and spread. In contrast, humoral immunity relies on antibodies produced by B cells to neutralize free-floating viruses before they enter host cells. While both responses are vital for effective immunity, cell-mediated mechanisms provide essential protection against intracellular pathogens that evade antibody detection.

Related terms

T lymphocytes: A type of white blood cell that plays a central role in the immune response, specifically involved in recognizing and responding to specific antigens.

Antigen-presenting cells: Cells that capture, process, and present antigens on their surface using MHC molecules, which are essential for T cell activation.

Major histocompatibility complex (MHC): A set of cell surface proteins that present peptide fragments of proteins to T cells, crucial for the recognition of foreign molecules by the immune system.