Your Body’s DefensesYour Body’s Defenses

Fighting off PathogensFighting off Pathogens

Infectious DiseaseInfectious Disease

Caused by a pathogen (bacteria, virus, Caused by a pathogen (bacteria, virus, fungus, microscopic parasites…)fungus, microscopic parasites…)

Transmitted from one individual to anotherTransmitted from one individual to anotherAir currents, physical contact, contaminated Air currents, physical contact, contaminated

food or water, animal bite, etc.food or water, animal bite, etc.

Your Immune System: The “Basics”

Nonspecific DefensesNonspecific Defenses

What does “nonspecific” refer toWhat does “nonspecific” refer to?? These defenses provide general protection These defenses provide general protection

against any and all pathogens.against any and all pathogens. The defense is not tailored or targeted to a The defense is not tailored or targeted to a

specific antigen (pathogen).specific antigen (pathogen). Examples:Examples:

Skin and skin secretionsSkin and skin secretions MucousMucous FeverFever

These either destroy or inhibit the These either destroy or inhibit the growth/reproduction of pathogens.growth/reproduction of pathogens.

Specific Defense: Immune SystemSpecific Defense: Immune System

The immune system The immune system has many has many components.components.

The white blood The white blood cells necessary to cells necessary to mount a targeted mount a targeted attack first form in attack first form in the bone marrow.the bone marrow.

They then They then differentiate and take differentiate and take on various jobs.on various jobs.

The body is exposed to countless The body is exposed to countless antigens; each is uniqueantigens; each is unique

BacteriaBacteria

Each pathogen has an antigenEach pathogen has an antigen

Antigen: any substance that initiates an Antigen: any substance that initiates an immune response.immune response.

May be:May be:ProteinsProteinsLipidsLipidsCarbohydratesCarbohydrates

Typically, antigens are molecules at the Typically, antigens are molecules at the surface of the pathogensurface of the pathogen

MacrophagesMacrophages

These cells ingest (“gobble”) These cells ingest (“gobble”) pathogenspathogens..This helps rid the body of some pathogens. This helps rid the body of some pathogens.

(nonspecific).(nonspecific).More importantly, More importantly, when a macrophage when a macrophage

ingests a pathogen it displays pieces of ingests a pathogen it displays pieces of the pathogen at its surfacethe pathogen at its surface. (specific). (specific)

Otherwise known as an “Antigen Presenting Otherwise known as an “Antigen Presenting Cell”.Cell”.

Macrophages call to action the Macrophages call to action the Helper T cellsHelper T cells

Helper T cells coordinate the 2 major Helper T cells coordinate the 2 major activities of the immune response.activities of the immune response. Cell mediated immunity: cytotoxic (“killer”) T cells Cell mediated immunity: cytotoxic (“killer”) T cells

destroy infected body cells.destroy infected body cells. Humoral immunity: plasma cells (activated B cells) Humoral immunity: plasma cells (activated B cells)

release antibodies.release antibodies. The helper T cell is activated by “lock and The helper T cell is activated by “lock and

key” interaction with a macrophage.key” interaction with a macrophage. It then releases chemical signals It then releases chemical signals

(cytokines/interleukins) inducing the correct T and B (cytokines/interleukins) inducing the correct T and B cells to multiply.cells to multiply.

The attack is now targeted to a The attack is now targeted to a specific antigen specific antigen

(Find the enemy! Destroy it!)(Find the enemy! Destroy it!)

Antigen

Helper T Cells call in the “Killers”Helper T Cells call in the “Killers”

Helper T cells activate Helper T cells activate cytotoxic T cellscytotoxic T cells that that have receptors have receptors matching the shape of matching the shape of the antigen.the antigen.

These “killer” T cells These “killer” T cells then then find and destroy find and destroy cells that have been cells that have been infected.infected.

Helper T cells also bring B cells Helper T cells also bring B cells into the fightinto the fight

By chemical signaling By chemical signaling and “lock and key” and “lock and key” recognition, the recognition, the helper T cells helper T cells activate B cells.activate B cells.

B cells then produce B cells then produce millions of millions of antibodies, antibodies, each with each with the same shape-the the same shape-the shape that is shape that is complementary to the complementary to the antigen.antigen.

When activated, B cells with the correct receptor divide by mitosis, producing many identical B cells.

Some produce antibodies immediately and fight off the initial infection.

Others are memory cells that mount an attack against a 2nd infection.

AntibodiesAntibodies

Produced and secreted into the blood by B Produced and secreted into the blood by B cells.cells.

The antibodies are Y-shaped proteins; The antibodies are Y-shaped proteins; each has a specific shape that binds to each has a specific shape that binds to an antigenan antigen..

The antibodies latch onto antigens The antibodies latch onto antigens causing pathogens to clump together.causing pathogens to clump together.Makes for easier destruction and “clean-up”Makes for easier destruction and “clean-up”

ImmunityImmunity After initial exposure to a After initial exposure to a

specific antigen (primary specific antigen (primary response), a person is response), a person is “immune”.“immune”.

The pathogen may invade The pathogen may invade the body again, but does the body again, but does not cause illness.not cause illness.

The secondary response is The secondary response is fast and effective (due to fast and effective (due to memory cells), resulting in memory cells), resulting in no symptoms.no symptoms.

Immunity can be acquired by:

1) Fighting off an illness caused by the pathogen.

2) Vaccination: causes a primary response to the antigen, without causing illness.

Primary vs. Secondary ResponsePrimary vs. Secondary Response

Vaccination (a.k.a. Immunization)Vaccination (a.k.a. Immunization)

VaccineVaccine: contains : contains inactivated bacterial inactivated bacterial toxins, or weakened microbestoxins, or weakened microbes, etc. that , etc. that will will stimulate an immune responsestimulate an immune response, , because they are seen as antigens.because they are seen as antigens.Because the modified pathogens are Because the modified pathogens are

harmless, vaccines don’t result in illness. harmless, vaccines don’t result in illness. The memory cells produced during the The memory cells produced during the

primary response will protect you against primary response will protect you against future illness caused by the pathogen.future illness caused by the pathogen.

Common VaccinesCommon Vaccines

MeaslesMeasles MumpsMumps PolioPolio ChickenpoxChickenpox RubellaRubella TetanusTetanus Hepatitis BHepatitis B Influenza (many types)Influenza (many types) DiphtheriaDiphtheria

Short-term ImmunityShort-term Immunity

Passive immunity:Passive immunity:A pregnant woman passes antibodies to her A pregnant woman passes antibodies to her

child through the placenta. A nursing mother child through the placenta. A nursing mother passes antibodies to the child through breast passes antibodies to the child through breast milk.milk.

An injection of antibodies from an immune An injection of antibodies from an immune animal or human is given to a person. animal or human is given to a person. Example: a person bit by an animal with Example: a person bit by an animal with rabies is injected with antibodies.rabies is injected with antibodies.