Lecture Notes: Cell-Mediated Response in Immunity

Introduction

• Focus on the cell-mediated response or cellular response of immunity.
• Emphasizes the role of T lymphocytes (T cells).
• Second line of defense in the immune response.

T Lymphocytes (T Cells)

• Involved in the specific immune response.
• Produced in the bone marrow.
• Mature in the thymus.
• Active in response to specific antigens.

Antigen-Presenting Cells (APCs)

• Cells that display non-self antigens on their surface.
• Could be:
  • Infected body cells presenting viral antigens.
  • Phagocytes like macrophages after phagocytosis.
  • Cells from a transplanted organ.
  • Abnormal cells such as cancer cells.

Cell-Mediated Response

• Involves the response of T cells to antigens presented on APCs.
• T cells do not respond to free-floating antigens.
• Steps involved:
  1. Pathogen engulfed by phagocytosis.
  2. Antigens presented on the surface of the phagocyte, creating an APC.
  3. Helper T cells bind to antigens on APCs.
  4. Binding activates helper T cells which divide by mitosis, forming clones.

Role of Helper T Cells

• Helper T cells stimulate other immune responses:
  • Activate B cells (involved in the humoral response).
  • Stimulate macrophages for further phagocytosis.
  • Some differentiate into memory cells, retaining memory of the antigen.
  • Some become cytotoxic (killer) T cells.

Cytotoxic T Cells (Killer T Cells)

• Destroy abnormal or infected cells.
• Release protein called perforin that creates pores in cell membranes.
• Cause cell death by disrupting cell membrane integrity.
• Important in viral infections where viruses replicate in body cells.
• Example: Sore throat in colds due to cytotoxic T cells destroying infected throat cells.

Summary

• Cell-mediated response involves T lymphocytes responding to antigens on APCs.
• Helper T cells differentiate into active immune cells.
• Cytotoxic T cells release perforin to destroy infected cells.

Additional Resources

• Practice questions available at Miss Astrick's website.
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