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INNATE IMMUNITY

Overview of Innate Immune Cells

Macrophage
  • Definition: Highly phagocytic cells that serve as the sentinel of the immune system.
  • Functions: Produces powerful inflammatory cytokines, which play a key role in the immune response.
Natural Killer Cells
  • Definition: Cells that perform innate monitoring of tissues for viral or tumor invasion.
  • Functions:
    • Recognizes and destroys infected or cancerous cells through direct cytotoxic activity.
    • Uses perforins and granzymes to induce cell death.
Neutrophils, Basophils, and Eosinophils
  • Definition: Specialized inflammatory cells of the immune system; also known as polymorphonuclear cells.
  • Functions:
    • Involved in the rapid-response phase of inflammation following infection.
    • Release of chemokines that help direct other immune cells to sites of infection.

Cytokines Involved in Innate Immunity

  • IL-6: A pro-inflammatory cytokine important in the immune response.
  • TNF-a: Tumor Necrosis Factor alpha, involved in systemic inflammation and activation of other immune cells.
  • Interferon (IFN):
    • IFN-y: Involved in the activation of macrophages and the enhancement of antigen presentation.
    • IFN-a/ß: Type I interferons, involved in antiviral responses.
  • TGF-beta: Transforming Growth Factor-beta, involved in immune regulation and inflammation.
  • IL-10: An anti-inflammatory cytokine that helps regulate immune responses.
Mechanisms of Innate Immune Response
  • Physical Barrier:
    • Acts as the first line of defense; includes skin and mucous membranes.
    • Breaches can occur through wounds, burns, scratches, or bites, leading to subsequent immune responses.
  • Inflammatory Response:
    • Occurs within 0-4 hours following the immune insult.
    • Involves chemokines and complement activation.
  • Complement System:
    • Components such as C3a and C5a contribute to recruiting immune cells to the site of infection.
    • Opsonization of Pathogens:
    • Mediated by complement proteins C3b and C4b, enhancing phagocytosis.
    • MAC Complex: (Membrane Attack Complex) facilitates lysis of pathogens through complement proteins C5b to C9.

ADAPTIVE IMMUNITY

Overview of Adaptive Immune Cells

CD8 T Cell
  • Common Name: Cytolytic "Killer T Cell"
  • Functions:
    • Activated CD8 T cells can directly induce apoptosis in infected target cells through the release of perforins and granzymes.
CD4 T Cell
  • Common Name: T-helper cell
  • Functions:
    • Activated by cytokines produced from CD4 T cell responses, they produce powerful inflammatory cytokines that assist in activating CD8 T cells and B cells.
    • Key in orchestrating the adaptive immune response.
B Cell
  • Common Name: Antibody-producing cell
  • Functions:
    • Activated B cells produce antibodies that specifically target and neutralize pathogens, contributing to humoral immunity.
Dendritic Cells
  • Functions:
    • Serve as antigen-presenting cells (APCs) that activate acquired immunity by presenting processed antigens to T cells.
Regulatory T Cell
  • Common Name: T-Reg
  • Functions:
    • Specific to antigens the body should not respond against; they produce anti-inflammatory cytokines to maintain immune tolerance and prevent autoimmunity.
NK-T Cells
  • Overview:
    • These cells are a hybrid of innate and adaptive immune cells.
    • They possess a T cell receptor (TCR) with a limited range of variability yet can be activated without classical antigen presentation.
Key Cytokines in Adaptive Immunity
  • IFN-y: Important in activating macrophages and enhancing the immune response.
  • Granzyme: Serine proteases that induce apoptosis in target cells.

Summary of Immune System Functions

  • The immune system comprises both innate and adaptive elements, working collaboratively to detect and respond to pathogens.
  • Cytokines play an essential role in regulating and mediating these immune responses, ensuring effective pathogen clearance while maintaining immune homeostasis.