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Biology -Entrance Exam ( Universidad de Navarra) - unit 6 (1)

Unit 7 - Immunology

Introduction to Immunology

  • Definition: The study of how the body protects itself against infectious diseases from microorganisms (bacteria, viruses, protozoa, fungi) and parasites (helminths).

  • Initial Barriers: Physical barriers like skin, and substances like saliva and tears neutralize bacteria.

    • Mucosal tissues protect internal areas (e.g., lungs, gut) with mucus that traps pathogens.

    • Cilia in airways transport contaminants away.

Immune System Overview

  • Components:

    • Innate Immune System: Provides rapid, general responses to infections.

    • Adaptive Immune System: Develops specific responses and immune memory.

  • Both systems work cooperatively; the innate system alerts the adaptive system.

Immune Tissues

  • Origin of immune cells: Bone marrow (hematopoietic stem cells).

    • T Lymphocytes: Mature in the thymus (primary lymphoid tissue).

  • Secondary Lymphoid Tissues:

    • Lymph Nodes: Monitor lymph for infection.

    • Spleen: Acts like a lymph node for blood.

    • MALT: Important for mucosal immune responses (gut, airways).

Innate Immunity

Key Cells and Mechanisms

  • Mast Cells & Basophils: Activated to secrete histamine, involved in inflammatory responses.

  • Phagocytes:

    • Neutrophils and Macrophages: Respond to infection, perform phagocytosis (engulf pathogens).

  • Pattern Recognition: Uses Pattern Recognition Receptors (PRRs) like Toll-like receptors (TLRs) to identify pathogens.

Complement System

  • Composed of proteins that enhance the immune response.

  • Complement Pathways:

    • Classical, alternative, and mannose-binding lectin pathways.

Adaptive Immunity

Lymphocytes

  • T Lymphocytes (T Cells): Mature in the thymus.

  • B Lymphocytes (B Cells): Mature in bone marrow.

    • Each cell becomes specific to a unique antigen.

  • Helper T Cells: Activate and shape immune responses; classified into subtypes (Th1, Th2, Th17).

Antigen-Presenting Cells (APCs)

  • Major APCs: Dendritic cells, macrophages, B cells.

  • Process and present antigens to T cells via MHC molecules.

Cellular and Humoral Responses

  • Cellular Response: Cytotoxic T cells target infected or malignant cells.

  • Humoral Response: B cells produce antibodies following T cell activation.

Immune Memory

  • Memory Cells: Formed after primary response for quick reactivation upon re-exposure to pathogens.

  • Cytokines: Proteins facilitating communication in immune responses.

Immune Dysfunction

Types

  • Inborn Immunodeficiencies: Genetic disorders like Severe Combined Immunodeficiency (SCID).

  • Autoimmunity: Immune system attacks self-tissues (e.g., rheumatoid arthritis).

Pathologies

  • Autoimmune Diseases: Includes type 1 diabetes, multiple sclerosis.

Nonspecific Innate Immunity

Physical Defenses

  • Barriers: Skin, mucous membranes prevent pathogen entry.

  • Skin Structure: Epidermis protects through keratin production.

Chemical Defenses

  • Sebum: Oil secreted by skin, provides additional barriers.

  • Enzymes: Salivary and digestive enzymes eliminate pathogens.

Antigen Definition & Properties

  • Antigen: A substance that can trigger an immune response. Includes proteins, carbohydrates, and other molecules recognized as foreign.

Characteristics of Antigens

  1. Foreign Nature: Recognized as non-self.

  2. Chemical Nature: Proteins are highly immunogenic, while polysaccharides are moderate.

  3. Molecular Size: Immunogenicity generally requires a size >5000 Da.

  4. Complexity and Rigidity: More complex and rigid molecules are more immunogenic.

  5. Molecular Determinants: Antigenic determinants (epitopes) bind to antibody receptors.

Types of Antigens

  • Exogenous Antigens: From outside the host (e.g., pathogens).

  • Endogenous Antigens: Produced within the host's own cells (e.g., from normal metabolism).

  • Autoantigens: Body's own proteins mistaken for foreign (causing autoimmune diseases).

  • Tumor Antigens: Unique surfaces of cancer cells triggered by mutations.

Production of Monoclonal Antibodies

Overview

  • Monoclonal Antibodies (mAbs): Engineered from single B cell clones targeting specific antigens.

  • Types:

    • Murine, Chimeric, Humanized, and Fully Human.

Applications

  • Treatment of cancers, autoimmune diseases, and diagnostic tools.

Limitations

  • Risk of immune responses to non-human components (e.g., HAMA reaction).

Mechanisms of Immune Response

  1. Recognition: Identification of foreign antigens.

  2. Activation: Initiation of immune responses.

  3. Attack: Targeting and elimination of pathogens.

  4. Control: Regulation and resolution of immune reactions after pathogen elimination.