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.