Innate and Adaptive Immunity, Vaccination, and Immune Disorders: Study Guide (Ch. 15-18)

Innate Immunity

Microbial Antagonism

Microbial antagonism refers to the competition between normal microbiota and potential pathogens for resources and space, which helps protect the host from infection.

• Definition: The inhibition of pathogenic microbes by the normal microbiota.

• Example: Lactobacillus in the vagina produces acid, lowering pH and inhibiting pathogens.

White Blood Cells (Leukocytes): Types and Functions

• Basophils: Release histamine; involved in inflammation and allergic responses.

• Monocytes: Differentiate into macrophages and dendritic cells; phagocytic.

• Macrophages: Engulf and digest pathogens and debris; antigen presentation.

• Neutrophils: Most abundant; phagocytic; first responders to infection.

• Eosinophils: Combat parasitic infections; involved in allergic responses.

Lines of Defense in Innate Immunity

• First Line: Physical and chemical barriers (skin, mucous membranes, secretions).

• Second Line: Cellular defenses (phagocytes, NK cells), inflammation, fever, antimicrobial proteins (complement, interferons).

Dendritic Cells

• Role: Antigen-presenting cells that initiate adaptive immune responses.

• Location: Found in tissues in contact with the external environment (skin, mucosa).

Inflammation and Tissue Repair

• Signs: Redness, heat, swelling, pain, loss of function.

• Processes: Vasodilation increases blood flow; increased permeability allows immune cells to access tissues; tissue repair restores function.

• Degranulation: Release of granule contents (e.g., histamine) from cells like mast cells and basophils.

Complement Cascade (Classical Pathway)

• Trigger: Antigen-antibody complexes.

• Molecules: C1, C2, C4, C3, C5–C9.

• Consequences: Opsonization, inflammation, cell lysis via membrane attack complex (MAC).

Interferons (Alpha and Beta)

• Respond to: Viral infections.

• Mechanism: Induce antiviral proteins in neighboring cells, inhibiting viral replication.

Phagocytosis

• Cells: Neutrophils, macrophages, dendritic cells.

• Process: Chemotaxis → Adherence → Ingestion → Digestion → Exocytosis.

Granulocytes vs. Agranulocytes

• Granulocytes: Neutrophils, eosinophils, basophils (contain visible granules).

• Agranulocytes: Lymphocytes, monocytes (lack visible granules).

• Granules: Contain enzymes and mediators for immune responses.

Opsonization

• Definition: Coating of pathogens with opsonins (e.g., antibodies, complement) to enhance phagocytosis.

Eosinophilia

• Definition: Elevated eosinophil count.

• Indicates: Parasitic infection or allergic reaction.

Natural Killer (NK) Lymphocytes

• Definition: Lymphocytes that kill virus-infected and tumor cells without prior sensitization.

• Mechanism: Release perforin and granzymes to induce apoptosis in target cells.

Adaptive (Acquired) Immunity

Key Terms and Definitions

• Antigen: Substance that elicits an immune response.

• Agglutination: Clumping of particles, such as cells, by antibodies.

• Immune Memory: Ability of the immune system to respond more rapidly to previously encountered antigens.

• Primary Immune Response: First response to an antigen; slower and less robust.

• Secondary Immune Response: Faster, stronger response upon re-exposure to the same antigen.

• Antigen Presentation: Display of antigen fragments on MHC molecules to T cells.

• Interferon, Interleukin, TNF, Growth Factors: Types of cytokines with various immune functions.

• Autoantigens: Self-antigens; normally not targeted by the immune system.

• Lysozyme: Enzyme that breaks down bacterial cell walls.

• Apoptosis: Programmed cell death.

Cytokines

• Definition: Small proteins that mediate and regulate immunity, inflammation, and hematopoiesis.

• Types: Interleukins (ILs), interferons (IFNs), tumor necrosis factors (TNFs), growth factors.

Adaptive Immune Response

• Adapts to: Specific pathogens or antigens encountered by the host.

• Features: Specificity, diversity, memory, self/non-self recognition.

Antigen Processing and Presentation

• Exogenous Antigens: Processed by antigen-presenting cells (APCs) and presented on MHC II to helper T cells.

• Endogenous Antigens: Processed within infected cells and presented on MHC I to cytotoxic T cells.

Autoantigens and Clonal Deletion

• Prevention of Autoimmunity: Self-reactive lymphocytes are eliminated during development (clonal deletion).

Humoral vs. Cell-Mediated Immunity

• Humoral (Antibody-Mediated): B cells produce antibodies; effective against extracellular pathogens.

• Cell-Mediated: T cells (especially cytotoxic T cells) target infected or abnormal cells.

Helper T Cells (Th) Interactions

• With Cytotoxic T Cells: Provide signals (cytokines) for activation and proliferation.

• With B Cells: Stimulate antibody production and class switching.

Major Histocompatibility Complex (MHC)

• MHC I: Found on all nucleated cells; presents endogenous antigens to cytotoxic T cells.

• MHC II: Found on APCs; presents exogenous antigens to helper T cells.

Types of Immunity

• Innate (Non-specific): Present from birth; immediate response.

• Acquired (Specific, Adaptive): Develops after exposure; specific and has memory.

• Active Immunity: Host produces own immune response (natural infection or vaccination).

• Passive Immunity: Transfer of antibodies (maternal, antiserum).

• Naturally-acquired: Through infection or maternal antibodies.

• Artificially-acquired: Through vaccination or antibody therapy.

Antibodies (Immunoglobulins, Ig)

• IgM: First antibody produced; effective in agglutination and complement activation.

• IgG: Most abundant; crosses placenta; provides long-term immunity.

• IgA: Found in mucosal areas and secretions (tears, saliva, breast milk).

• IgE: Involved in allergic responses and defense against parasites.

• IgD: Functions mainly as a B cell receptor.

Immunization and Immune Testing

Key Terms

• Adjuvant: Substance that enhances the body's immune response to an antigen.

• Pathogen: Disease-causing microorganism.

• Attenuation: Reduction of virulence of a pathogen for use in vaccines.

• Variolation: Early method of immunization using material from smallpox lesions; first used in China and the Middle East.

Historical Contributions

• Edward Jenner: Developed the first vaccine (smallpox) using cowpox virus.

• Louis Pasteur: Developed vaccines for rabies and anthrax; advanced the concept of attenuation.

Vaccine Types

Type	Description	Advantages	Disadvantages
Attenuated (Live)	Weakened pathogen	Strong, long-lasting immunity	Risk in immunocompromised; possible reversion
Inactivated (Killed)	Killed pathogen	Safe, stable	Weaker response; may need boosters
Toxoid	Inactivated toxin	Protects against toxin-mediated diseases	Requires boosters

Primary vs. Secondary Immune Response

• Primary: First exposure; slower, lower antibody levels.

• Secondary: Subsequent exposure; rapid, high antibody levels due to memory cells.

ELISA Testing

• Purpose: Detects presence of antigens or antibodies in a sample.

• Process: Antigen or antibody is immobilized; enzyme-linked antibody binds; substrate added; color change indicates positive result.

Immune Disorders and HIV/AIDS

Hypersensitivities (Types I-IV)

Type	Mechanism	Example
I (Immediate)	IgE-mediated, mast cell degranulation	Allergies, anaphylaxis
II (Cytotoxic)	Antibody-mediated cell destruction	Hemolytic anemia, transfusion reactions
III (Immune Complex)	Immune complex deposition	Serum sickness, lupus
IV (Delayed)	T cell-mediated	Contact dermatitis, TB test

Mast Cells and Degranulation

• Mast Cells: Granulocytes involved in allergic responses; release histamine upon activation.

• Degranulation: Release of granule contents (e.g., histamine) into tissues, causing inflammation.

Sensitization

• Definition: Initial exposure to allergen leads to IgE production and binding to mast cells.

Histamine

• Definition: Inflammatory mediator released by mast cells and basophils.

Tuberculin (TB) Testing

• Positive Response: Indicates prior exposure to Mycobacterium tuberculosis or vaccination.

• Mechanism: Delayed-type hypersensitivity (Type IV); T cell-mediated response to injected antigen.

Transplantation Terms

• Xenograft: Transplant from different species.

• Allograft: Transplant from same species, different individual.

• Isograft: Transplant from genetically identical individual (e.g., identical twin).

• Autograft: Transplant from same individual.

Hemolytic Disease of the Newborn

• Mechanism: Maternal anti-Rh antibodies cross placenta and destroy fetal red blood cells.

Autoimmune Diseases

• Susceptibility: Genetic and environmental factors.

• Examples:

  • Systemic Lupus Erythematosus (SLE): Autoantibodies against nuclear components; systemic symptoms.

  • Rheumatoid Arthritis: Autoantibodies against joint tissues; chronic inflammation.

  • Type I Diabetes Mellitus: Autoimmune destruction of pancreatic beta cells.

Immunodeficiencies

• Primary: Genetic or developmental defects (e.g., SCID).

• Acquired: Result from infection (e.g., HIV), malnutrition, or immunosuppressive therapy.

HIV/AIDS

• Target: CD4+ T cells (helper T cells).

• Viral Particle: RNA genome, reverse transcriptase, integrase, protease enzymes.

• Mechanism of Infection: Attachment to CD4 and co-receptors → fusion → reverse transcription → integration into host genome → production of new virions → release.

• HAART/ART Therapy: Combination antiretroviral therapy reduces viral load and slows disease progression.

HIV Enzymes and Functions

• Reverse Transcriptase: Converts viral RNA to DNA.

• Integrase: Integrates viral DNA into host genome.

• Protease: Processes viral proteins for assembly of new virions.

Additional info:

• For the complement cascade, the classical pathway is triggered by antigen-antibody complexes, leading to a cascade of proteolytic activations resulting in the formation of the membrane attack complex (MAC), which lyses pathogens.

• ELISA (Enzyme-Linked Immunosorbent Assay) is widely used for diagnostic purposes, such as detecting HIV antibodies or antigens in patient samples.

• HAART (Highly Active Antiretroviral Therapy) or ART (Antiretroviral Therapy) typically includes drugs targeting reverse transcriptase, integrase, and protease to inhibit different stages of the HIV life cycle.