Defense Against Infectious Defense Against Infectious DiseasesDiseases

IB BiologyIB Biology

Natural Human DefensesNatural Human Defenses

To prevent infection, we employ a To prevent infection, we employ a variety of defenses to ward off variety of defenses to ward off infection:infection:– Physical DefensePhysical Defense

– Mechanical DefenseMechanical Defense

– Chemical DefenseChemical Defense

– Biological DefenseBiological Defense

Physical DefensePhysical Defense

SkinSkin– Tough outer layer of dead cellsTough outer layer of dead cells– Contains keratin and very little moistureContains keratin and very little moisture– Rarely penetrated by microorganismsRarely penetrated by microorganisms

Skin ChemicalsSkin Chemicals– Tears (lachrymal glands) for dilution Tears (lachrymal glands) for dilution – Sebum (sebaceous glands) w/ fatty acidsSebum (sebaceous glands) w/ fatty acids– Mucus (goblet cells) trap airborne pathogensMucus (goblet cells) trap airborne pathogens

Mechanical DefenseMechanical Defense

Nasal hairs filter air passing through nasal Nasal hairs filter air passing through nasal passagespassages

Cilia in lungs sweep away microbes Cilia in lungs sweep away microbes trapped in mucustrapped in mucus

Chemical DefenseChemical Defense

Tears, mucus, saliva, and sweat all Tears, mucus, saliva, and sweat all contain microorganism inhibitorscontain microorganism inhibitors

Lysosyme: enzyme found in many Lysosyme: enzyme found in many secretionssecretions– Catalyzes the hydrolysis of molecules in the Catalyzes the hydrolysis of molecules in the

cell walls of bacteriacell walls of bacteria

Lactate (in sweat) slows bacterial growthLactate (in sweat) slows bacterial growth

HCl in gastric juice kills most pathogensHCl in gastric juice kills most pathogens

Biological DefenseBiological Defense

Harmless colonies of symbiotic bacteria Harmless colonies of symbiotic bacteria live on skin and mucus membranes and live on skin and mucus membranes and inhibit pathogenic microbesinhibit pathogenic microbes

Harmless bacteria also compete with Harmless bacteria also compete with pathogenic bacteria for nutrientspathogenic bacteria for nutrients

Broad-spectrum antibiotics destroy the Broad-spectrum antibiotics destroy the good with the bad bacteria, leaving us with good with the bad bacteria, leaving us with fewer natural defensesfewer natural defenses

Immune ResponseImmune ResponseWhen a pathogen does sneak by the When a pathogen does sneak by the defenses, the body mounts an immune defenses, the body mounts an immune responseresponseEach pathogen has distinctive protein or Each pathogen has distinctive protein or glycoprotein markers called antigens glycoprotein markers called antigens which trigger the immune responsewhich trigger the immune responseAntigen: complex molecules on or Antigen: complex molecules on or produced by pathogens that generate an produced by pathogens that generate an immune response in hostimmune response in host– Self AntigensSelf Antigens– Non-Self AntigensNon-Self Antigens

Cell Mediated ImmunityCell Mediated Immunity

White Blood Cells InvolvedWhite Blood Cells Involved– Lymphocytes: recognize and react with Lymphocytes: recognize and react with

antigensantigensT-Lymphocytes (for cell-mediated immunity)T-Lymphocytes (for cell-mediated immunity)

B-Lymphocytes (for antibody production)B-Lymphocytes (for antibody production)

– Macrophages: universal phagocytosis of Macrophages: universal phagocytosis of foreign objectsforeign objects

Also called phagocytic leucocytesAlso called phagocytic leucocytes

Cell Mediated Immunity (Stages)Cell Mediated Immunity (Stages)

Macrophages engulf pathogensMacrophages engulf pathogensPathogen antigens can become imbedded Pathogen antigens can become imbedded in macrophage membranein macrophage membraneSpecialized T-lymphocytes recognize and Specialized T-lymphocytes recognize and fit with antigens fit with antigens T-lymphocytes go active and replicate T-lymphocytes go active and replicate rapidly (cloning those T-lymphocytes that rapidly (cloning those T-lymphocytes that recognize the antigens)recognize the antigens)Clones differentiate into 4 cell typesClones differentiate into 4 cell types

T-Lymphocyte Cell TypesT-Lymphocyte Cell Types

Cytotoxic T-cells: “killer cells” destroy the Cytotoxic T-cells: “killer cells” destroy the antigen (virus or cancer) directly by attaching antigen (virus or cancer) directly by attaching to them and releasing the chemical perforinto them and releasing the chemical perforin

Helper T-cells: direct the attack, summon Helper T-cells: direct the attack, summon macrophages, promote T and B cell activitymacrophages, promote T and B cell activity

Memory T-cells: no action, but multiply rapidly Memory T-cells: no action, but multiply rapidly if there’s a re-infectionif there’s a re-infection

Suppressor T-cells: slow down/stop immune Suppressor T-cells: slow down/stop immune response when job is doneresponse when job is done

T-lymphocyte

(containing binding sites

that fit the antigen)

Infected Cell with Antigens

Or Pathogen

Or Macrophage with AntigensActivated or Sensitized T-cell

Rapid Mitotic Divisions

Differentiation

Cytotoxic T-Cells

Helper T-Cells

Memory T-Cells

Suppressor T-Cells

Destroy pathogenic antigens

Coordinate attack by T-cells

Used in future

infections

Slow/Stop immune

response

Antibody Mediated ImmunityAntibody Mediated Immunity

Antibody: glycoprotein (immunoglobulin)Antibody: glycoprotein (immunoglobulin)– Attaches to specific antigen to destroy it or render it Attaches to specific antigen to destroy it or render it

incapacitated until a macrophage arrivesincapacitated until a macrophage arrives

Involved Cell Type: B-LymphocyteInvolved Cell Type: B-Lymphocyte– Stimulated by helper T-cellsStimulated by helper T-cells– Respond to antigens attached to macrophagesRespond to antigens attached to macrophages

3 Types of B-Lymphocytes3 Types of B-Lymphocytes– Plasma B-cells: secrete antibodiesPlasma B-cells: secrete antibodies– Memory B-cells: long-lived, respond rapidly to future Memory B-cells: long-lived, respond rapidly to future

infections by the same antigeninfections by the same antigen– Dividing B-cells: produce more B-cellsDividing B-cells: produce more B-cells

Antibody Mediated Immunity Antibody Mediated Immunity (Stages)(Stages)

Macrophages engulf pathogenMacrophages engulf pathogen

Pathogen antigens can become imbedded in Pathogen antigens can become imbedded in macrophage membranemacrophage membrane

B-lymphocytes activated when they contact B-lymphocytes activated when they contact antigensantigens

Activated B-cells clone & some convert to Activated B-cells clone & some convert to plasma B-cellsplasma B-cells

Plasma B-cells produce and secrete antibodiesPlasma B-cells produce and secrete antibodies

Antibodies circulate and attach to antigens and Antibodies circulate and attach to antigens and destroy them or form agglutinations destroy them or form agglutinations (described later)(described later)

B-lymphocyte

(containing binding sites that fit with pathogenic antigen)

Pathogen or Macrophage with pathogen antigens

Rapid Mitosis (cloning)

Differentiation

Plasma B-cells Memory B-cells Dividing B-cells

antibodies

Secondary ResponseSecondary Response

For cell-mediated and antibody-mediated For cell-mediated and antibody-mediated immunities, the secondary response is immunities, the secondary response is faster (second time you get the pathogen)faster (second time you get the pathogen)

Memory T-cells and B-cells ensure rapid Memory T-cells and B-cells ensure rapid cloning and differentiationcloning and differentiation

Antibody produced by a plasma B-cell

Antibodies and AntigensAntibodies and Antigens

The effect of an antibody attaching to an The effect of an antibody attaching to an antigen is first a shape change in the antigen is first a shape change in the antibodiesantibodiesNext, the antibody may cause Next, the antibody may cause agglutination (antigens will stick together)agglutination (antigens will stick together)This can stimulate phagocytosis by This can stimulate phagocytosis by neutrophils or macrophagesneutrophils or macrophagesIt can also prevent pathogens from It can also prevent pathogens from attaching to cell membranesattaching to cell membranes

Agglutination

Uses of AntibodiesUses of Antibodies

Also called Monoclonal AntibodiesAlso called Monoclonal Antibodies

DiagnosisDiagnosis– Detection of HIV with anti-HIV antibodiesDetection of HIV with anti-HIV antibodies– Detection of cardiac isoenzyme in suspected Detection of cardiac isoenzyme in suspected

heart-attack casesheart-attack cases– Detection of HCG for pregnancy test kitsDetection of HCG for pregnancy test kits

Uses of Antibodies (cont.)Uses of Antibodies (cont.)

TreatmentTreatment– Targeting of cancer cells with drugs attached Targeting of cancer cells with drugs attached

to monoclonal antibodiesto monoclonal antibodies– Emergency treatment of rabies or cancerEmergency treatment of rabies or cancer– Blood and tissue typing for transplant Blood and tissue typing for transplant

compatibilitycompatibility– Purification of industrially produced interferonPurification of industrially produced interferon

Interferons are glycoproteins used in response to Interferons are glycoproteins used in response to challenges by pathogens. They assist by inhibiting challenges by pathogens. They assist by inhibiting viral replication.viral replication.

Vaccinations/ImmunizationsVaccinations/Immunizations

Vaccinations or immunizations generate Vaccinations or immunizations generate an immune response, but not to a live an immune response, but not to a live pathogen (dead, inactive, or synthetic)pathogen (dead, inactive, or synthetic)Immune response stimulates memory T Immune response stimulates memory T and B cells, which remainand B cells, which remainSecondary response in the event of an Secondary response in the event of an actual pathogen infection is fast and actual pathogen infection is fast and strongstrongSymptoms not typically noticedSymptoms not typically noticed

Vaccination Pros & ConsVaccination Pros & ConsProsPros– Dramatically reduces odds of pathogenic infections Dramatically reduces odds of pathogenic infections

with symptomswith symptoms– Potential to wipe out dangerous communicable Potential to wipe out dangerous communicable

diseases (smallpox)diseases (smallpox)– Reduces cost of disease treatmentReduces cost of disease treatment

ConsCons– Possibility of becoming infected (if vaccination Possibility of becoming infected (if vaccination

contains any live pathogens)contains any live pathogens)– Vaccine cost, access, administration logisticsVaccine cost, access, administration logistics– Overall erosion of immune system?Overall erosion of immune system?– A variety of other theoretical drawbacksA variety of other theoretical drawbacks

MMR VaccineMMR Vaccine

MMR = Measles, Mumps, RubellaMMR = Measles, Mumps, RubellaProsPros– Measles is a nasty disease, good to vaccinateMeasles is a nasty disease, good to vaccinate

ConsCons– Most boys don’t need Rubella vaccineMost boys don’t need Rubella vaccine– Most girls don’t need Mumps vaccineMost girls don’t need Mumps vaccine– Girls don’t need Rubella vaccine until sexual Girls don’t need Rubella vaccine until sexual

maturitymaturity– Potentially contributes to autism Potentially contributes to autism

(hypothesized)(hypothesized)

Chicken Pox VaccineChicken Pox VaccineProsPros– In adults and some children who haven’t had In adults and some children who haven’t had

it before, it can be a dangerous illnessit before, it can be a dangerous illness– Good for those with compromised immune Good for those with compromised immune

systemssystems– Saves the discomfort of getting ill Saves the discomfort of getting ill

ConsCons– Its a common illness in children and its Its a common illness in children and its

usually mildusually mild– Re-exposure boost immune response, so Re-exposure boost immune response, so

vaccination could decrease bothvaccination could decrease both– Boosters? Unknown need.Boosters? Unknown need.

Influenza (Flu) VaccineInfluenza (Flu) Vaccine

ProsPros– Beneficial for those who get flu every yearBeneficial for those who get flu every year– Beneficial for those who have dramatic flu Beneficial for those who have dramatic flu

symptoms when they get the flusymptoms when they get the flu– Beneficial for the very young and the very old Beneficial for the very young and the very old

and those with weakened immune systemsand those with weakened immune systems

ConsCons– Higher (than most vaccines) incidence of Higher (than most vaccines) incidence of

contracting a live virus from the vaccinecontracting a live virus from the vaccine– Enabling immune system to become too Enabling immune system to become too

relaxed?relaxed?