Study Guide

🧠 IMMUNITY & HOST DEFENSE STUDY GUIDE

🛡 I. THREE LINES OF HOST DEFENSE1. First Line (Innate – External)

  • Purpose: Prevent pathogen entry

  • Components:

    • Physical barriers (skin, mucous membranes)

    • Chemical barriers (enzymes, acids)

    • Biological barriers (normal microbiota)

2. Second Line (Innate – Internal)

  • Purpose: Destroy pathogens that enter body

  • Includes:

    • Phagocytes

    • Inflammation

    • Fever

    • Antimicrobial proteins

3. Third Line (Adaptive Immunity)

  • Purpose: Specific, targeted immune response

  • Features:

    • Specificity

    • Memory

    • Lymphocytes (B & T cells)

🧬 MARKERS & IMMUNITY

  • Marker: A molecule (usually protein) on a cell surface used for identification

  • Importance:

    • 2nd line: Helps immune cells recognize “self vs non-self”

    • 3rd line: Essential for antigen recognition (T cells rely on markers like MHC)

🧍 BODY SYSTEMS IN IMMUNITY

  • Lymphatic system

  • Circulatory system

  • Integumentary system

  • Respiratory system

  • Digestive system

🧪 LYMPHATIC SYSTEMStructure:

  • Lymph vessels

  • Lymph nodes

  • Spleen

  • Thymus

Function:

  • Transports lymph (fluid with immune cells)

  • Filters pathogens

  • Houses lymphocytes

Connection to Circulatory System:

  • Returns fluid to bloodstream

  • Works closely with blood to circulate immune cells

🩸 CELLS OF INNATE IMMUNITYKey Cells:

  • Neutrophils

  • Macrophages

  • Natural Killer (NK) cells

Mononuclear Phagocyte System:

  • Network of phagocytic cells (monocytes → macrophages)

  • Engulfs and destroys pathogens

Histiocytes:

  • Tissue-resident macrophages

  • Difference: Stay fixed in tissues instead of circulating

🔥 CYTOKINES

  • Small signaling proteins

  • Coordinate immune response

Examples:

  • Pro-inflammatory: Interleukin-1 (IL-1)

  • Anti-inflammatory: Interleukin-10 (IL-10)

🧱 FIRST LINE OF DEFENSEComponents:

  1. Physical barriers

  2. Chemical barriers

  3. Microbiological barriers

Body Systems Involved:

  • Skin (integumentary)

  • Respiratory

  • Digestive

  • Genitourinary

Normal Microbiota:

  • Compete for nutrients

  • Produce antimicrobial substances

⚔ SECOND LINE OF DEFENSE4 Categories:

  1. Cells (phagocytes, NK cells)

  2. Inflammation

  3. Fever

  4. Antimicrobial molecules

🦠 PHAGOCYTOSIS (Steps)

  1. Chemotaxis

  2. Adherence

  3. Engulfment

  4. Phagosome formation

  5. Fusion with lysosome

  6. Destruction

  7. Exocytosis

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🔥 INFLAMMATION (Steps)

  1. Injury

  2. Vasodilation

  3. Increased permeability

  4. WBC migration

  5. Tissue repair

🌡 FEVER Mechanism:

  • Pyrogens → hypothalamus → increased temperature

Benefit:

  • Slows pathogen growth

  • Enhances immune activity

🧪 ANTIMICROBIAL PRODUCTS

  • Lysozyme

  • Interferons

  • Complement proteins

  • Defensins

Complement System (1 Sentence)

  • A protein cascade that enhances immune responses by promoting inflammation, opsonization, and pathogen lysis.

Interferons (1 Sentence)

  • Proteins released by infected cells that inhibit viral replication in neighboring cells.

🧠 THIRD LINE (ADAPTIVE IMMUNITY) Key Differences:

  • Specific vs general

  • Has memory

  • Slower initial response

🧬 ANTIGEN TERMS

  • Antigen: Any molecule recognized by immune system

  • Immunogen: Antigen that triggers response

  • Epitope: Specific part of antigen recognized

🔄 STAGES OF ADAPTIVE RESPONSE

  1. Recognition

  2. Activation

  3. Response

  4. Memory

🧾 MHC (2 sentences)

  • Major Histocompatibility Complex proteins present antigen fragments on cell surfaces.

  • They allow T cells to recognize infected or abnormal cells.

🧫 B & T CELL MATURATION

  • B cells: Bone marrow

  • T cells: Thymus

🧬 CLONAL SELECTION & DELETION

  • Selection: Activation and replication of specific lymphocytes

  • Deletion: Elimination of self-reactive cells

🧬 BCR vs TCR

  • BCR: Binds free antigens

  • TCR: Requires antigen presentation (via MHC)

🧬 ANTIGEN-PRESENTING CELLS

  • Dendritic cells

  • Macrophages

  • B cells

⚔ T CELLS

  • Helper (CD4): Coordinate immune response

  • Cytotoxic (CD8): Kill infected cells

🧬 B-CELL ACTIVATION (Summary)

  • Antigen binding → helper T activation → plasma cells + memory cells

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🧪 ANTIBODIESStructure:

  • Y-shaped protein

  • Variable region (binds antigen)

  • Constant region

Functions:

  • Neutralization

  • Opsonization

  • Agglutination

  • Complement activation

🧾 ANTIBODY TYPES

  • IgG (most abundant)

    • Only Ig to cross the placenta

  • IgA (mucosal)

  • IgM (first responder)

  • IgE (allergies)

  • IgD (B cell receptor role)

📈 PRIMARY vs SECONDARY RESPONSE

  • Primary: slow, low response

  • Secondary: fast, strong (memory)

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💉 IMMUNE STATES

  • Naturally acquired active

  • Naturally acquired passive

  • Artificially acquired active

  • Artificially acquired passive

💉 VACCINESQualities:

  • Safe

  • Effective

  • Long-lasting immunity

Types:

  • Whole-agent: live attenuated, inactivated

  • Subunit: toxoid, recombinant

🧪 IMMUNOPATHOLOGY

  • Disease caused by immune dysfunction

Types:

  1. Hypersensitivity

  2. Immunodeficiency

⚠ HYPERSENSITIVITIESTypes:

  1. Type I (allergy, IgE)

  2. Type II (cytotoxic)

  3. Type III (immune complex)

  4. Type IV (delayed)

🌼 ALLERGIESInfluences:

  • Genetics

  • Environment

IgE Conditions:

  • Asthma

  • Hay fever

  • Food allergies

⚠ ANAPHYLAXIS

  • Local vs systemic (systemic = more fatal due to shock)

🚫 PREVENT TYPE I

  • Avoid allergen

  • Antihistamines

  • Epinephrine

🩸 TYPE II DETAILS

  • Antibody + complement → cell lysis

Rh Factor:

  • Causes hemolytic disease

  • Prevented with RhoGAM

🧬 TYPE IV EXAMPLE

  • Contact dermatitis (poison ivy)

🧫 TRANSPLANTS

  • Autograft

  • Isograft

  • Allograft

  • Xenograft

Diseases:

  • Host vs graft

  • Graft vs host

🧠 AUTOIMMUNE DISEASES

  • Lupus

  • Rheumatoid arthritis

  • Type 1 diabetes

🛑 IMMUNODEFICIENCIES

  • Primary: genetic

  • Secondary: acquired (HIV, malnutrition)

🧪 MICROBIAL IDENTIFICATION

🔬 3 MAJOR CATEGORIES

  1. Direct methods: detect pathogen itself

  2. Indirect methods: detect immune response

  3. Molecular methods: detect genetic material

⚠ FACTORS AFFECTING IDENTIFICATION

  • Sample quality

  • Timing

  • Contamination

🏥 ROLE OF NURSE

  • Proper sample collection

  • Correct labeling

  • Timely transport

🧫 DIRECT METHODS

  • Microscopy

  • Culture

🧪 BIOCHEMICAL TESTING

  • Identifies microbes via metabolic traits

  • Example: sugar fermentation tests

Drawbacks:

  • Time-consuming

  • Some pathogens don’t grow in culture

🧬 SEROLOGY

  • Study of antibodies in blood

  • Based on antigen-antibody binding

Secondary Antibody Tests:

  • ELISA

  • Western blot

🧬 MOLECULAR METHODSPCR:

  • Amplifies DNA → highly sensitive

Hybridization:

  • DNA probes bind specific sequences

Whole Genome Sequencing:

  • Identifies pathogen by full DNA analysis

🩸 PCR FOR BLOODSTREAM INFECTIONS

  • Faster diagnosis

  • Detects low levels of pathogens

  • More accurate than culture

🧠 THREE METHODS

  • Phenotypic → observable traits

  • Immunologic → antigen-antibody

  • Genotypic → DNA-based

🧫 DIRECT IDENTIFICATION

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  • Gram stain

  • Acid-fast stain

  • KOH stain

🧪 CULTURE METHODS

  • Selective media

  • Differential media

🧪 KIRBY-BAUER

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  • Measures antibiotic effectiveness

🧪 SEROLOGY (IMMUNOLOGIC)

  • Antigen-antibody reactions

🧪 ELISA

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  • Uses enzyme-linked antibodies

  • Color change = positive

🧪 PCR (GENOTYPIC)

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  • Amplifies DNA

  • Fast & sensitive

🧬 HYBRIDIZATION

  • DNA probes bind target sequence