CM

Notes on Immune Responses and Transplantation

Immune Responses and Transplantation

Overview of Immune Response

  • Complex Mechanism of Defense
    • Critical for maintaining health.
    • Common problems occur when altered:
    • Inflammation
    • Infection
    • Tissue integrity

Immunity

  • Definition: The body’s ability to resist disease.
  • Functions:
    • Defense
    • Homeostasis
    • Surveillance

Antigens

  • Definition: Substances that elicit an immune response.
  • Composition: Primarily proteins, but can also include:
    • Polysaccharides
    • Lipoproteins
    • Nucleic acids
  • Unique: Each individual's antigens are unique, allowing the body to recognize itself.

Types of Immunity

  • Innate Immunity:
    • Present at birth.
    • Acts as the first-line defense against pathogens.
    • Quick response.
  • Acquired Immunity:
    • Developed immunity classified into:
    • Active: Immunity developed after infection or vaccination.
    • Passive: Immunity passed from mother to child or through antibody injection.

Types of Acquired Specific Immunity

  • Natural Immunity:
    • Active: Contact with an antigen through actual infection (e.g., chickenpox).
    • Passive: Maternal transfer of antibodies (e.g., through breast milk).
  • Artificial Immunity:
    • Active: Immunization using vaccines.
    • Passive: Injection of serum containing antibodies from another person.

Organs of the Immune System

  • Central Lymphoid Organs:
    • Thymus Gland: Maturation of T lymphocytes.
    • Bone Marrow: Produces blood cells, including lymphocytes.
  • Peripheral Lymphoid Organs:
    • Lymph Nodes: Filter foreign material and circulate lymphocytes.
    • Spleen: Primary site for filtering blood antigens.
    • Tonsils and other lymphoid tissues (gut-associated, genital-associated, etc.).

Cells of the Immune Response

  • Mononuclear Phagocytes:
    • Role in capturing and processing antigens.
    • Include monocytes and macrophages.
  • Lymphocytes:
    • Produced in bone marrow; migrate to peripheral organs.
    • Differentiate into B (antibody-producing) and T (cell-mediated immune) lymphocytes.

Types of Lymphocytes

  • B Cells (10-20%): Plasma cells that produce antibodies.
  • T Cells (70-80%): Responsible for cell-mediated immunity against viruses and tumors; long-lasting immunity.
    • Types:
    • T Cytotoxic Cells (CD8): Attack infected cells.
    • T Helper Cells (CD4): Regulate immune responses.
  • Natural Killer (NK) Cells: Attack virus-infected and tumor cells.

Cytokines

  • Definition: Soluble factors secreted by white blood cells; act as messengers in the immune system.
  • Roles:
    • Regulate immune responses, hematopoiesis.
    • Can have both beneficial and detrimental effects (e.g., chronic inflammation).
  • Types of Cytokines:
    • Interleukins
    • Interferons
    • Tumor necrosis factor
    • Colony-stimulating factors
    • Erythropoietin

Immune Responses: Comparisons

  • Humoral Immunity:
    • Involves B cells and antibodies.
  • Cell-Mediated Immunity:
    • Involves T cells, macrophages, and NK cells.
  • Main Differences:
    • Humoral: Antibodies for extracellular pathogens.
    • Cellular: T cells for intracellular pathogens and tumor surveillance.

Secondary Immune Response

  • Faster response (1-3 days) due to memory cells.
  • Primarily involves IgG production, unlike the IgM produced during the primary response.

Immunosenescence

  • Effect of aging on immune response:
    • Reduced T-cell production and responsiveness.
    • Increased susceptibility to infections and autoimmunity.

Hypersensitivity Reactions

  • Histological Classification:
    • Type I: Immediate (e.g., anaphylaxis).
    • Type II: Antibody-mediated, causing tissue damage.
    • Type III: Immune complex-mediated reactions (e.g., lupus).
    • Type IV: Delayed responses involving T cells (e.g., contact dermatitis).

Anaphylaxis and Allergic Reactions

  • Manifestations:
    • Smooth muscle contraction, hypotension, increased vascular permeability.
  • Examples:
    • Allergic rhinitis, asthma, atopic dermatitis, hives, angioedema.

Summary of Hematopathology in Transplantation

  • Understanding immune responses is crucial in the context of organ transplantation and the management of transplant rejection through immunosuppressive therapies.