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IMMUNOLOGY OVERVIEW

  • Overview of various cell types involved in the immune response:

    • Lymphocytes: B cells, T cells, NK (Natural Killer) cells.

    • Granulocytes: Neutrophils, Eosinophils, Basophils.

    • Monocytes: Develop into macrophages and dendritic cells.

HEMATOPOIESIS

  • Location: Bone Marrow.

  • Stem Cells: Pluripotent stem cells differentiate into:

    • White Blood Cells (WBC)

    • Red Blood Cells (RBC)

    • Platelets.

  • Progenitor Cells: Myeloid progenitors lead to various cell types, such as:

    • Neutrophils (40-75% of leukocytes)

    • Basophils (<1%)

    • Monocytes (2-10%)

    • Lymphocytes (20-50%).

  • Large Reserves: Neutrophils stored in bone marrow released as needed, migrate to tissues for inflammation and repair.

OBJECTIVES OF IMMUNOLOGY

  • Describe the physiological function of the immune system.

  • Differentiate between:

    • Self and non-self.

    • Innate and adaptive immunity.

    • Central and peripheral organs.

    • Cellular and humoral immunity.

    • Responses to intracellular and extracellular pathogens.

    • Primary and secondary (memory) responses.

    • Active and passive immunity.

    • Natural and artificial immunity.

  • Outline a typical response to pathogens.

  • Describe the cells involved in immune functions, such as:

    • Neutrophil

    • Macrophage (MΦ)

    • Natural Killer (NK) cell

    • Mast Cell

    • Dendritic Cell (DC)

    • B Cell

    • T Cell.

  • Diagram phases of immune response under first and second exposure.

PURPOSE OF THE LECTURE

  • To learn basic principles of immunology to prepare for detailed discussions.

  • Recommended Reading: Basic Immunology: Functions & Disorders of the Immune System by Abbas & Lichtman, Chapter 1 (pages 1-22).

IMMUNITY

  • Definition: State or quality of being resistant to infections (immunity) derived from:

    • Previous exposure (adaptive immunity)

    • Inherent traits (innate immunity).

  • Process involves recognition of antigens as foreign (non-self) and elimination.

RELEVANT DEFINITIONS

  • Immune System: A collection of cells, molecules, and tissues involved in the immune response.

  • Immune Responses: Actions against antigens on pathogens (defensive mechanisms).

  • Adaptive Immunity: Antigen-specific lymphocyte response which includes a memory component.

  • Innate Immunity: Non-specific protection existing before infection occurs.

  • Antigen (Ag): Molecules recognized by antibodies or lymphocytes.

FUNCTIONS OF THE IMMUNE RESPONSE

  • Goals:

    • Prevent infection

    • Eradicate established infections.

  • Main Tasks:

    • Immunological Recognition

    • Contain & Eliminate (effector functions)

    • Immune Regulation

    • Immunological Memory.

RECOGNITION OF ANTIGENS: SELF VS. NON-SELF

  • Immune response: Targets non-self antigens, distinguished from “self” antigens.

  • Immunological Tolerance: The immune system's non-reaction to self antigens.

IMMUNE RESPONSE SIMPLIFIED CONCEPT MAP

  • Categories:

    • Innate Immunity:

    • Surface defenses: Physical barriers (skin), Chemical barriers (digestive enzymes).

    • Subsurface defenses: Cells (Monocytes, PMNs, NK cells), Proteins (Complement, Cytokines).

    • Adaptive Immunity:

    • Humoral Immunity: B lymphocytes (antibody production).

    • Cellular Immunity: T lymphocytes.

INTEGRATED SYSTEMS: INNATE & ADAPTIVE

  • Immune defense systems continuously surveil the body, differentiating self from non-self and employing responses for pathogen destruction.

CHARACTERISTICS OF INNATE vs. ADAPTIVE IMMUNITY

  • Innate Immunity:

    • Specificity: Limited; targets general patterns of infection.

    • Memory: None.

  • Adaptive Immunity:

    • Specificity: High; targets specific antigens.

    • Memory: Yes; retains information for faster responses on re-exposure.

TYPICAL MICROBIAL RESPONSE

  • Most microbes are effectively cleared by innate immunity, while adaptive immunity provides long-term protection and memory.

INNATE IMMUNITY

  • Response Conditions:

    • Rapid defenders acting before infection.

    • Inherent mechanisms; no memory.

  • Types of Cells:

    • Neutrophils:

    • Primary responders; survive ~24 hours; phagocytic; can lead to pus formation.

    • Macrophages:

    • Differentiate from monocytes; present in the tissue; phagocytic; long-lived.

    • Natural Killer Cells:

    • Recognize and kill infected or malignant cells via toxins.

    • Dendritic Cells:

    • Antigen processing; bore the bridge between innate and adaptive immunity.

    • Eosinophils:

    • Combat multicellular parasites; involvement in allergic reactions.

    • Basophils and Mast Cells:

    • Involved in inflammatory responses; release histamine.

ADAPTIVE IMMUNITY

  • Develops in response to infections; characterized by specificity and memory.

  • Key cells include lymphocytes (B and T cells) and antibodies.

  • Defining Features:

    1. Specificity for unique antigens.

    2. Memory response; distinguish previous and new infections.

    3. Exquisite adaptation to pathogen exposure.

LYMPHOID ORGANS/TISSUES

  • Organ types where lymphocytes mature and respond to infection include:

    • Appendix

    • Tonsils

    • Adenoids

    • Peyer's patches

    • MALT/GALT/BALT.

ADAPTIVE: HUMORAL & CELL-MEDIATED

  • Humoral responses involve antibodies produced by B cells.

  • Cell-mediated responses involve T cells that directly attack foreign antigens.

EXTRACELLULAR VS. INTRACELLULAR PATHOGENS

  • Extracellular Pathogens:

    • Vulnerable at epithelial surfaces, interstitial spaces, blood, lymph to antibodies, complement activation, and phagocytosis.

  • Intracellular Pathogens:

    • Vulnerable in cytoplasm to cytotoxic T lymphocytes or NK cells; vesicles targeted by T cells.

CARDINAL FEATURES OF ADAPTIVE IMMUNITY

  • Characteristics include:

    • Specificity to distinct antigens

    • Diversity in response capabilities

    • Clonal expansion and selection

    • Memory formation for quicker responses upon re-exposure

    • Nonreactivity to self to prevent autoimmunity.

CLONAL SELECTION

  • A process where circulating lymphocytes interact with pathogens, leading to the selection and proliferation of specific lymphocytes tailored to eliminate pathogens.

PRIMARY VERSUS SECONDARY RESPONSES

  • Differences in the immune response upon first exposure to a pathogen versus subsequent exposures, focusing on speed and effectiveness of memory response.

ACTIVE VS. PASSIVE & NATURAL VS. ARTIFICIAL IMMUNITY

  • Examples of each type to demonstrate how immunity can be acquired:

    • Active: Exposure to infections or vaccinations leads to memory formation.

    • Passive: Direct transfer of antibodies (e.g., maternal antibodies) that do not establish memory.

    • Natural: Occurs through natural exposure.

    • Artificial: Through vaccines or medical interventions.

NON-REACTIVITY – SELF/NON-SELF

  • The goal of immunological tolerance is to avoid reactions against self-antigens, achieved through immune cell development processes.

CASE PRESENTATIONS

  • Multiple case presentations depicting various stages of immune responses and symptoms related to infections, illustrating practical applications of immunology in clinical scenarios.

TEST YOURSELF EXERCISES

  • Evaluative questions on distinguishing between innate and adaptive immunity, cell functions, and general understanding of immune system components and their roles.

A BALANCED IMMUNE SYSTEM

  • Internal and external threats to the immune system and conditions resulting from overreaction (autoimmunity, allergies) and underreaction (infections, cancer).