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Immunity –Immunity –The War Against InfectionThe War Against Infection

Immunity: Immunity: ability of an ability of an organism to resist disease.organism to resist disease.

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

Antibodies:Antibodies: made in made in response to specific response to specific antigens; can inactivate the antigens; can inactivate the antigen that triggered the antigen that triggered the antibody formation.antibody formation.

The Body Fights Back: 2 WaysThe Body Fights Back: 2 Ways

Surface Barriers Keep Surface Barriers Keep Intruders OutIntruders Out• Prevents entry of antigens inside Prevents entry of antigens inside

our bodyour body• Skin, MucosaSkin, Mucosa

Two immune mechanisms:Two immune mechanisms:• Cell MediatedCell Mediated Immunity: Cell Immunity: Cell

activates itself to defend against the activates itself to defend against the attackattack

• HumoralHumoral Immunity: Cell produces Immunity: Cell produces antibodies carried in blood to antibodies carried in blood to combat the intrusioncombat the intrusion

The InvadersThe Invaders

The AntigenThe Enemy Invader

• Usually a bacteria or virus

The Warriors

Three Defense Systems:Three Defense Systems:

1.1.Macrophage cellsMacrophage cells

2.2.T cellsT cells

3.3.B cellsB cells

The Macrophage

Body's Radar

Type of cell normally present in the blood

Detects the enemy

and engulfs (eats) it

The WarriorsThe Warriors

The Warriors

The T-Helper CellCommunication Link

Communication Link Between the body's macrophages and B-cells

Inactivated in HIV infections

Macrophage Presents Antigen Macrophage Presents Antigen to T Cellsto T Cells

Virus

Virus

Virus

The B-CellThe War FactoryProduces antibodies

custom tailored for the type of enemy antigen

The Warriors

B-Cells in ActionB-Cells in Action

Virus

Virus

Virus

Virus

AntibodiesAntigen BustersDesigned to seek and

destroy the specific enemy antigen

Antibodies Need Help

ComplementSupport Troops Assists the

antibodies to neutralize the enemy antigen

Antibody Protein & Humoral ImmunityAntibody Protein & Humoral Immunity

Since antibodies circulate through the body fluids(humours), Since antibodies circulate through the body fluids(humours),

the protection afforded by B cells is called humoral immunity.the protection afforded by B cells is called humoral immunity.

Structure of antibodies (Y-shaped proteins)

So what does an So what does an antibody do?antibody do?

1.1. Binds to molecules Binds to molecules (antigens) on the surface (antigens) on the surface of invading organism.of invading organism.

2.2. Inactivates or renders the Inactivates or renders the microorganism susceptible microorganism susceptible to destruction by the to destruction by the immune system.immune system.

Review 1Review 1

What is the enemy called that invades the What is the enemy called that invades the cell?cell?

What keeps intruders out?What keeps intruders out?

What are the two kinds of immunity?What are the two kinds of immunity?

Surface Barriers or Mucosal Surface Barriers or Mucosal ImmunityImmunity

SkinSkin

CiliaCilia

Tears, Saliva, Urine.Tears, Saliva, Urine.

Sticky mucusSticky mucus

Stomach: Stomach: Hydrochloric AcidHydrochloric Acid

AnalogyAnalogy

Suppose the classroom is a body.Suppose the classroom is a body. All students are cells.All students are cells. Rats are Rats are AntigensAntigens.. Doors and Windows prevent them from entering Doors and Windows prevent them from entering

- - Surface BarriersSurface Barriers.. Some of you Some of you Tough onesTough ones (T-cells) (T-cells) will capture will capture

the rodents - the rodents - Cell-mediated ImmunityCell-mediated Immunity.. Some of you Some of you BrainiacsBrainiacs (B-cells) (B-cells) will call pest will call pest

control (control (AntibodiesAntibodies) to capture the rodents – ) to capture the rodents – Humoral ImmunityHumoral Immunity..

The Cells in BloodThe Cells in Blood

Source: National Library of Medicine*Lymphocyte not shown. Looks like a monocyte, except nucleus mostly fills the cell and does not have a notch in it.

The Role of NeutrophilsThe Role of Neutrophils

When a wound occurs, neutrophils migrate out of blood to rush to the wound and phagocytize (“eat”) the bacteria. This is what pus is made of.

“old” neutrophil surrounded by red blood cells

The Role of The Role of

Turn into MacrophagesTurn into Macrophages

Note the notch in the nucleus. Otherwise, it looks like a

lymphocyte.

MonocytesMonocytes EosinophilsEosinophilsAttack Internal ParasitesAttack Internal Parasites

Note the red granules in the cytoplasm.

The Role of MacrophagesThe Role of MacrophagesEngulf and then digest cellular debris and Engulf and then digest cellular debris and

microbes in the body tissues.microbes in the body tissues.

Note the irregular cell membrane. These are

monocytes in the bloodstream and once they

migrate into the tissues they become

macrophages.

The Role of PlateletsThe Role of PlateletsBlood ClottingBlood Clotting

They can clump together to form clots. No role in immunity.

LeukocytosisLeukocytosis

Leukocytosis: Leukocytosis: white blood cell count white blood cell count increasedincreased above the normal range.above the normal range.

It is not a disorder or a disease, but a It is not a disorder or a disease, but a signsign of of illness.illness.

It occurs in response to a wide variety of It occurs in response to a wide variety of conditions, including conditions, including viral, bacterial, fungal, or parasitic infectionviral, bacterial, fungal, or parasitic infectioncancer cancer Hemorrhage (internal bleeding)Hemorrhage (internal bleeding)exposure to certain medications or chemicals exposure to certain medications or chemicals

including steroids.including steroids.

LeukopeniaLeukopenia

LeukopeniaLeukopenia: a : a decreasedecrease in the number of in the number of circulating white blood cells in the blood.circulating white blood cells in the blood.

As white blood cells get “used up” during As white blood cells get “used up” during infection, leukopenia can place patients at infection, leukopenia can place patients at higher risk for infection.higher risk for infection.

Causes: Causes: Influenza, typhus, malaria, Influenza, typhus, malaria, HIVHIV, tuberculosis, dengue, Rickettsial , tuberculosis, dengue, Rickettsial

infections, enlargement of the spleen and folate deficiencies.infections, enlargement of the spleen and folate deficiencies. chemotherapy, radiation therapy, leukemia , myelofibrosis and chemotherapy, radiation therapy, leukemia , myelofibrosis and

anemia.anemia. many common medications like minocyclen. many common medications like minocyclen.

HIV (Human Immunodeficiency Virus)HIV (Human Immunodeficiency Virus)

HIV infection causes AIDS (HIV infection causes AIDS (Acquired Acquired ImmunoDeficiency SyndromeImmunoDeficiency Syndrome). ).

AIDS causes the immune system to fail, leading to life-AIDS causes the immune system to fail, leading to life-threatening opportunistic infections. threatening opportunistic infections.

Infection with HIV occurs by the transfer of blood, Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk.semen, vaginal fluid, pre-ejaculate, or breast milk.

The four major routes of transmission areThe four major routes of transmission are unprotected sexual intercourse,unprotected sexual intercourse, contaminated needles contaminated needles breast milkbreast milk transmission from an infected mother to her baby at birth.transmission from an infected mother to her baby at birth.

AIDSAIDS ( (Acquired ImmunoDeficiency SyndromeAcquired ImmunoDeficiency Syndrome))

Virus infects vital cells such as helper T Virus infects vital cells such as helper T cells and macrophages.cells and macrophages.

When When T cell numbers declineT cell numbers decline below a below a critical level,critical level, cell-mediated immunity is cell-mediated immunity is lostlost, and , and infectionsinfections with a variety of with a variety of opportunistic microbes appear.opportunistic microbes appear.

Cell-mediated immunityCell-mediated immunity

It is an immune response that It is an immune response that does not involve does not involve antibodiesantibodies, , but ratherbut rather the cells act as the killers the cells act as the killers themselves.themselves.

It protects the body by:It protects the body by:

Activating antigen-specific Activating antigen-specific T-cellsT-cells that destroy that destroy infected cells.infected cells.

Activating Activating macrophagesmacrophages that destroy that destroy intracellular pathogens.intracellular pathogens.

Activating Activating NK (Natural Killer)NK (Natural Killer) cells that release cells that release a protein that kills the target cellsa protein that kills the target cells

Review 3Review 3

What is Leukopenia and what does it What is Leukopenia and what does it cause?cause?

What immune response does not involve What immune response does not involve antibodies?antibodies?

Immune System ResearchImmune System Research

How do they test for antibodies?How do they test for antibodies?

ELISA TESTELISA TEST

Remove blood cells and use the fluid (serum) to test for presence of antibody.

A. Place target sample on a support

B. Add serum that has antibody against antigen being tested for. Antibody, if present, binds the antigen.

C. Add a second antibody (that was separately developed to react with the antibody/antigen complex in step B) binds it to the complex. Second antibody was also prepared with an enzyme attached to it.

D. This new complex is made visible by reacting it with an enzyme that converts it to a colored compound that you can see.