Understanding Immune Cell Surface Receptors

Apr 2, 2025

Lecture Notes: Immune Cell Surface Receptors

Overview of Immune Cell Receptors

  • Immune cells have a variety of surface receptors which allow them to sense and respond to pathogens and damaged cells.
  • Focus on 5 main categories of immune cell receptors:
    1. Antigen receptors
    2. Costimulatory receptors
    3. Inhibitory receptors
    4. Cytokine receptors
    5. Chemokine receptors

1. Antigen Receptors

  • Purpose: Sense infectious microbes and damaged/diseased self cells.
  • Types:
    • Pattern Recognition Receptors (PRRs):
      • Include Toll-like receptors (TLRs), NOD-like receptors (NLRs), C-type lectin receptors (CLRs), Rig-1-like receptors (RLRs).
      • Recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs).
      • PAMPs are unique to microbes, ensuring recognition by the immune system.
      • DAMPs are molecules like ATP or HMGB1 which signal cell damage.
    • Antigen-specific Lymphocyte Receptors:
      • Extremely specific due to genetic rearrangement in B and T cells.
      • Each B and T cell expresses one type, acting as a "specialist" for different antigens.

2. Costimulatory Receptors

  • Purpose: Provide an additional signal needed for immune cell activation.
  • Key Receptors:
    • CD28 on T cells binds to CD80/CD86 on antigen presenting cells (APCs).
    • ICOS (Inducible costimulator) on T cells, binds ICOS-ligand on APCs, crucial for CD4 T cells helping B cells.
    • CD40 on APCs binds CD40 ligand on T cells, vital for optimizing antibody production and sustaining activation.

3. Inhibitory Receptors

  • Purpose: Regulate immune responses to prevent damage to self tissues.
  • Key Receptors:
    • CTLA-4 on T cells binds CD80/CD86 with higher affinity than CD28, inhibiting activation.
    • PD-1 on activated T cells binds PD-L1/PD-L2 on various cells, promoting T cell apoptosis.
    • Regulate natural killer cell activity by balancing activation and inhibition.

4. Cytokine Receptors

  • Purpose: Enable long-distance communication between immune cells via cytokines.
  • Function: Dictate immune response type (bacterial, viral, or parasitic) and state (pro-inflammatory or tissue repair).
  • Critical for immune cell growth, development, and proliferation.

5. Chemokine Receptors

  • Purpose: Guide immune cells to infection or damage sites.
  • Structure: Typically large G-protein coupled receptors.
  • Function: Change cell adhesion and motility for migration to infected tissues.

Conclusion

  • Cytokines and chemokines are critical signaling molecules, warranting further detailed exploration in future discussions.

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