Immune system
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Immune System. Chapter 21. Immune System. Functional body system Structures are cells not organs Provides immunity Recognizes ‘self’ from ‘non-self’ Fights pathogens and infections Destroy cancer cells Isolate and remove foreign substances Divisions Innate immunity (non-specific)

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Immune System

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Immune system

Immune System

Chapter 21

Immune system1

Immune System

  • Functional body system

    • Structures are cells not organs

    • Provides immunity

  • Recognizes ‘self’ from ‘non-self’

    • Fights pathogens and infections

    • Destroy cancer cells

    • Isolate and remove foreign substances

  • Divisions

    • Innate immunity (non-specific)

    • Adaptive immunity (specific)

Innate immunity

Innate Immunity

  • External defenses prevent entry

    • Skin

    • Mucous membranes

  • Internal defenses prevent/inhibit spread

    • Identified by surface carbs or proteins

    • Types

      • Phagocytes and natural killer (NK) cells

      • Inflammation (chemicals) and fever

      • Antimicrobial proteins

External defenses

External Defenses

  • Most efficient when unbroken/uninjured

  • Skin

    • Keratinized stratified squamous

  • Mucous membranes (chemical barriers)

    • Lines body cavities w/external openings

    • Produce wide range of chemicals

      • Sebaceous and sweat glands

      • Gastric juices, urine, and vaginal secretions

      • Salivary and lacrimal lysozyme secretions

      • Nasal cilia

  • Table 21.2



  • Macrophages (monocytes)

    • Wander through tissues (free)

    • Kupffer cells in liver and microglia in brain (fixed)

    • Resilient fighters

  • Neutrophils

    • Need exposure to infectious substances

    • Self sacrifice fighters

  • Eosinophils

    • Against parasitic worms

  • Mast cells

    • Local inflammatory response w/ pathogen exposure (allergies)

    • Release histamine, heparin, and proteases



  • Microbe is engulfed  phagosome

    • Phagocyte adheres to PM identifiers

    • Complement proteins and antibodies assist  opsonization

  • Phagosome fuses to lysosome  phagolysosome

  • Digestion

    • Respiratory burst needed for complex microbes

      • Helper T cells stimulate macrophages to produce

      • Increase pH to activate additional enzymes

    • Neutrophils produce defensinsto pierce PM

  • Exocytosis

  • Fig 21.2

Natural killer nk cells

Natural Killer (NK) Cells

  • Large, granular lymphocytes

  • Recognize and attack any ‘non-self’ cells (non-specific)

    • Cancer and viral cells

  • Perforins secreted to puncture PM

  • Induce apoptosis, programmed cell death

  • Enhance inflammatory response

Inflammatory response

Inflammatory Response

  • Clean up area and isolate/stop spread

  • Process

    • Histamine released by damaged tissues

    • Local vessel(s) vasodilation and permeability increase

      • Hyperema from increased blood flow (Redness and heat)

      • Clotting factors & antibodies (exudate) into tissues (edema)

        • Swelling presses on nerves  releasing prostoglandins (pain)

        • Antihistamines and aspirin/acetaminophen reduces

    • Phagocytes attracted

    • Fig 21.3

Phagocyte attraction

Phagocyte Attraction

  • Leukocytosis

    • Chemical signals increase neutrophil number

  • Margination

    • Neutrophils cling to capillary walls in injured area

    • Cell adhesion molecules (CAM’s) signal location and facilitate attachment

  • Diapedesis

    • Neutrophils move from blood to tissue

  • Chemotaxis

    • Attracts WBC’s to area  phagocytosis

      • Monocytes follow neutrophils  macrophages

      • Pus with bad infections



  • Systemic response to pathogen invasion

  • Leukocytes & macrophages release pyrogens to signal hypothalamus

  • High is dangerous

    • Denaturation of proteins (enzymes)

  • Moderate can be beneficial

    • Metabolic rate up = tissue repair rate up

    • Liver & spleen withhold iron & zinc = starves microbe

Antimicrobial proteins interferons

Antimicrobial Proteins: Interferons

  • Synthesized by infected cells

    • Enter neighboring cells to ‘interfere’ w/ viral reproduction

  • Not virus specific

  • Activate macrophages and NK cells too

Antimicrobial proteins complement

Antimicrobial Proteins: Complement

  • ‘Complements’ innate and adaptive defenses

  • 20+ inactive blood proteins

  • Activation

    • Classical pathway: activates through antigen/antibody binding

    • Alternate pathway: proteins directly attach to antigen

  • Result

    • Lyse many cell types (‘self’ are protected)

      • Protein complex produces a pore in PM

      • H2O floods in

    • Amplifies inflammatory response

    • Opsonization

Adaptive defenses

Adaptive Defenses

  • Attacks specific foreign substances

    • Longer reaction (antigen exposure)

    • Systemic protection (blood stream residence)

    • Permanent protection (‘memory’)

  • Mechanisms

    • Humoral immunity utilizes antibodies

    • Cellular immunity utilizes lymphocytes and other phagocytes



  • Molecules/cells eliciting adaptive immune response

    • Antigenic determinants provide signal

      • Immunogenicity: stimulates lymphocyte and antibody production

      • Reactivity: react with lymphocytes and antibodies

  • Types

    • Complete

      • Biological macromolecules, pollen, and microorganisms

    • Incomplete (haptens)

      • Smaller molecules that bind to ‘self’ selves

      • Cause hypersensitivity or allergies

Mhc proteins

MHC Proteins

  • Basis for ‘self’ and ‘non-self’ identification

    • Major histocompatibility complex genes encode

    • Unique to all individuals

  • Synthesized in the ER and transported to the PM for display

    • Class I on all body cells

    • Class II on dendritic cells, macrophages, and B-cells

Lymphocytes revisited

Lymphocytes (revisited)

  • Produced in red bone marrow from hemocytoblasts

  • Develop immunocompetence in primary lymphoid organs

    • B-cells in bone marrow and T-cells in thymus

    • Multiple antigen receptors

  • Migrate to secondary lymphatic organs

    • Antigen binding completes differentiation

      • Learn self-tolerance through positive & negative selection

  • Effector or memory cells free to wander

Antigen presenting cells apcs

Antigen-Presenting Cells (APCs)

  • Dendritic cells, macrophages, and B-cells

  • Functions

    • Engulf antigens for T-cell presentation

      • Fragments join MHC proteins on PM surface

      • Enables visualization of antigen by T-cell

    • Self/non-self complex recognized by T-cell

      • Binding signals differentiation

  • Key to initiating adaptive immunity

Humoral immune response

Humoral Immune Response

  • Antigen challenge when B-cell first meets antigen

  • Clonal selection forms …

    • Plasma cells  antibodies circulate to ‘flag’ antigens

    • Memory cells  quicker repeat response

  • Occurs in spleen or lymph nodes

Immunological memory

Immunological Memory

  • Primary immune response

    • Antigen challenge

  • Secondary immune response

    • Stronger, faster, & longer

Humoral immunity 2 0

Humoral Immunity 2.0

  • Active immunity

    • B-cells encounter antigens and MAKES antibodies

      • Natural exposure causes symptoms & suffering

      • Artificial exposure from dead or attenuated (vaccines)

    • Examples of each?

  • Passive immunity

    • Antibodies WITHOUT antigen exposure

      • Naturally b/w mother and fetus/infant

      • Artificially through pre- or post-injection

    • Examples of each?



  • Produce by B-cells AFTER antigen challenge

    • Also known as immunoglobins (Igs)

  • 4 looping polypeptides

    • Identical light (2) and heavy (2) chains

    • Variable regions (2 per)

      • Bind antigen

    • Constant regions

      • Basis for class distinction (5)

      • Determine functioning

  • Functions

    • Recognize and bind antigens

    • Inactivation of antigens

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( and WH Freeman (

Antibody classes

Antibody Classes

  • IgM

    • Produced 1st by plasma cells; activates complement

  • IgA

    • Prevents pathogen attachment in mucus membranes

  • IgD

    • B-cell surface receptor to activate other B-cells

  • IgG

    • Most abundant for 1° and 2° responses; fetal immunity, activates complement

  • IgE

    • Responsible for allergies due to histamine release

Targeting antigens

Targeting Antigens

  • Precipitation

    • Phagocyte accessibility increase due to weight increase

  • Lysis (by complement)

    • Antibodies (which?) insert MAC into PM (earlier)

    • Enhance inflammatory response and opsonization

  • Agglutination

    • Clumps antigens for phagocytes

  • Neutralization

    • Bind/block attachment and exotoxin sites on antigen

    • Slows until phagocytosis

Cell mediated immune response

Cell-Mediated Immune Response

  • Works when cells are infected w/antigen

    • Requires ‘visualization’ of antigen for T-cell

  • T-cells distinguished by glycoprotein receptors

    • CD8 cells

      • Recognize class I MHC proteins (all body cells)

      • Become cytotoxic/killer T-cells (TC)

    • CD4 cells

      • Recognize class II MHC proteins (APCs)

      • Become helper T-cells (TH) or memory T-cells

T cell types

T-Cell Types

  • Cytotoxic T-cells directly attacks and kills

    • Perforins or apoptosis signal to ‘non-self’ cells

  • Helper T-cells elicit immune responses

    • Stimulate B-cells to proliferate

    • Activate CD8 cells w/ co-stimulatory chemicals

    • Increase macrophage strength, cytokine release, & amplify innate defenses

  • Memory T-cells remain to prepare for future exposure

  • Regulatory T-cells (TReg) inhibit immune response

    • Stops once unnecessary

    • Autoimmune disease protection

T cell differentiation and cloning

T-Cell Differentiation and Cloning

  • Differentiation requires double recognition

    • Self and non-self

      • Class I MHC proteins with endogenous antigens

      • Class II MHC proteins with exogenous antigens

    • CD8 and CD4 recognize and bind accordingly

  • Co-stimulation signals clones to be produced

    • Additional T-cell binding or cytokine/interleuken release

    • Lack of causes T-cell tolerance and prevents mitosis

Organ transplants

Organ Transplants

  • Key is to maximize match while reducing rejection

    • Blood type (ABO and Rh) AND MHC protein

  • Grafts exchange tissues b/w recipient and donor

    • Autografts: same person, different site

    • Isografts: genetically identical donor

    • Allografts: not genetically identical, but same species

    • Zenografts : different species

  • Post - immunosuppressive therapy lessons the rejection

    • Drugs to suppress inflammation response and mitosis

    • Increases chance of secondary infection



  • Hypersensitivity to otherwise harmless antigens (allergens)

    • Animal dander (skin cells) and saliva proteins

    • Dust (mite feces) and pollen

  • 2 stage reaction

    • Sensitization: IgE produced but no response

    • Allergic response: antigen binds IgE mast cells and histamine released

  • Triggers inflammatory response = symptoms



  • Immune response to harmless antigens that result in tissue damage

  • Immediate occurw/i seconds of exposure (IgE)

    • Atopy: allergic reaction not in direct allergen contact

    • Anaphylactic shock: system wide inflammatory response

  • Subacute occur 1 - 3 hours after exposure (IgG and IgM)

    • Cytotoxic (type II): binding signals phagocytosis and lysis (mismatched blood)

    • Immune complex (type III): antigen-antibody complex can’t be removed

  • Delayed occur 1 – 3 days after exposure

    • Contact dermatitis: hapten (incomplete antigen) exposure

    • Tuberculosis skin test: hardened lesion post-injection if sensitization had occurred



  • Reductions of immune system cell numbers

  • Examples

    • Severe Combined Immunodificiency(SCID): genetic abnormality that reduces B-cell number

    • Hodgkin’s disease: B-cell cancer that depresses lymph nodes

    • Acquired Immune Disease (AIDS): destroys CD4 receptor cells (helper T-cells primarily)

      • Caused by human immunodeficiency virus (HIV)

Autoimmune disease

Autoimmune Disease

  • Body recognizes ‘self’ selves as ‘non-self’ and attacks

  • Examples:

    • Multiple sclerosis: white matter (myelin) in CNS

    • Myasthenia gravis: skeletal muscle ACh receptors

    • Graves’ disease: excessive amounts of fluid by thyroid

    • Type I diabetes: pancreatic insulin producing cells

    • Systemic lupus erythematosus(SLE): chronic system inflammation (kidneys, heart, lungs, and skin common)

    • Rhematoid arthritis: bones and cartilage of joints

Immune response summary

Immune Response Summary

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