ImmunityImmunity

What is immunity?What is immunity?

Immunity is the body's ability to fight Immunity is the body's ability to fight off harmful micro-organisms –off harmful micro-organisms –PATHOGENS- that invade it. PATHOGENS- that invade it.

The immune system produces The immune system produces antibodies or cells that can deactivate antibodies or cells that can deactivate pathogens.pathogens.

Fungi, protozoans, bacteria, and viruses Fungi, protozoans, bacteria, and viruses are all potential pathogens.are all potential pathogens.

What advantage do pathogens What advantage do pathogens have over humans?have over humans?

All have a short life span and All have a short life span and reproductive time.reproductive time.

So what?So what?

What is an infectious disease?What is an infectious disease?

AnAn infectious diseaseinfectious disease is one in which is one in which minute organisms, invisible to the minute organisms, invisible to the naked eye, invade and multiply naked eye, invade and multiply within the body.within the body.

Many of these organisms areMany of these organisms are contagiouscontagious, , that is they spread that is they spread between people in close contact. between people in close contact.

The first person to identify microbes The first person to identify microbes as causing disease was as causing disease was Robert KochRobert Koch..

We still use We still use Koch’s PostulatesKoch’s Postulates in in disease identification. disease identification.

Koch’s PostulatesKoch’s Postulates1.1. Pathogen must be found in the host in Pathogen must be found in the host in

every case.every case.

2.2. Pathogen must be isolated from the host Pathogen must be isolated from the host and grown in pure culture.and grown in pure culture.

3.3. When placed in a healthy host, pathogen When placed in a healthy host, pathogen produced in pure culture must cause the produced in pure culture must cause the disease in the host.disease in the host.

4.4. Pathogen must be isolated from the new Pathogen must be isolated from the new host and shown to be the original host and shown to be the original pathogen.pathogen.

Endemic diseasesEndemic diseases are those found normally are those found normally in a population.in a population.

For example…….For example…….

AnAn epidemic diseaseepidemic disease is a disease that many is a disease that many people acquire over a short period of time. people acquire over a short period of time.

For example………For example………

AA pandemic diseasepandemic disease is a world-wide is a world-wide epidemic disease.epidemic disease.

For example……….For example……….

An An antibioticantibiotic is a chemical substance is a chemical substance derivable from a mold or bacterium derivable from a mold or bacterium that kills microorganisms and cures that kills microorganisms and cures infectionsinfections..

The Immune SystemThe Immune System - includes all - includes all parts of the body that help in the parts of the body that help in the recognition and destruction of recognition and destruction of foreign materials.  White blood cells, foreign materials.  White blood cells, phagocytes and lymphocytes, bone phagocytes and lymphocytes, bone marrow, lymph nodes, tonsils, marrow, lymph nodes, tonsils, thymus, and your spleen are all part thymus, and your spleen are all part of the immune system.  of the immune system.  

First-Line DefensesFirst-Line Defenses / /Innate Immune Innate Immune SystemSystem-- The body's first line of defense The body's first line of defense against pathogens uses mostly physical against pathogens uses mostly physical and chemical barriers such as and chemical barriers such as

Skin – acts as a barrier to invasionSkin – acts as a barrier to invasion Sweat – has chemicals which can kill Sweat – has chemicals which can kill

different pathogens. different pathogens. Tears - have lysozyme which has powerful Tears - have lysozyme which has powerful

digestive abilities that render antigens digestive abilities that render antigens harmless. harmless.

Saliva – also has lysozyme.Saliva – also has lysozyme. Mucus - can trap pathogens, which are Mucus - can trap pathogens, which are

then sneezed, coughed, washed away, or then sneezed, coughed, washed away, or destroyed by chemicals. destroyed by chemicals.

Stomach Acid – destroys pathogensStomach Acid – destroys pathogens

Second-Line DefensesSecond-Line Defenses - If a pathogen - If a pathogen is able to get past the body's first line is able to get past the body's first line of defense, and an infection starts, the of defense, and an infection starts, the body can rely on it's second line of body can rely on it's second line of defense.  This will result in what is defense.  This will result in what is called an………. called an……….

Inflammatory responseInflammatory response causes causes Redness - due to capillary dilation Redness - due to capillary dilation

resulting in increased blood flow resulting in increased blood flow

Heat - due to capillary dilation Heat - due to capillary dilation resulting in increased blood flowresulting in increased blood flow

Swelling – due to passage of plasma Swelling – due to passage of plasma from the blood stream into the from the blood stream into the damaged tissuedamaged tissue

Pain – due mainly to tissue destruction Pain – due mainly to tissue destruction and, to a lesser extent, swelling. and, to a lesser extent, swelling.

Third-Line DefensesThird-Line Defenses - - Sometimes the second Sometimes the second line of defense is still not enough and the line of defense is still not enough and the pathogen is then heading for the body's last pathogen is then heading for the body's last line of defense, the line of defense, the immune systemimmune system.  .  

The The immune systemimmune system recognizes, attacks, recognizes, attacks, destroys, and remembers each pathogen that destroys, and remembers each pathogen that enters the body.  It does this by making enters the body.  It does this by making specialized cells and antibodies that render the specialized cells and antibodies that render the pathogens harmless. pathogens harmless.

   Unlike the first line and second line defense Unlike the first line and second line defense

the immune system differentiates among the immune system differentiates among pathogens. pathogens.

For each type of pathogen, the immune For each type of pathogen, the immune system produces cells that are specific for that system produces cells that are specific for that particular pathogen.particular pathogen.   

An An antibodyantibody is a protein produced in response is a protein produced in response to an antigen.to an antigen.

AntigensAntigens are are macromoleculesmacromolecules that elicit an that elicit an immune response in the body. The most immune response in the body. The most common antigens are proteins and common antigens are proteins and polysaccharides.polysaccharides.

AntigensAntigens can enter the body from the can enter the body from the environment. These includeenvironment. These include

inhaled macromolecules (e.g., proteins on cat inhaled macromolecules (e.g., proteins on cat hairs that can trigger an attack of asthma in hairs that can trigger an attack of asthma in susceptible people)susceptible people)

ingested macromolecules (e.g., shellfish ingested macromolecules (e.g., shellfish proteins that trigger an allergic response in proteins that trigger an allergic response in susceptible people)susceptible people)

molecules that are introduced beneath the skin molecules that are introduced beneath the skin (e.g., on a splinter or in an injected vaccine)(e.g., on a splinter or in an injected vaccine)

antigens can be generated within the antigens can be generated within the cells of the body. These includecells of the body. These include

proteins encoded by the genes of proteins encoded by the genes of viruses that have infected a cell viruses that have infected a cell

aberrant proteins that are encoded aberrant proteins that are encoded by mutant genes; such as mutated by mutant genes; such as mutated genes in cancer cells genes in cancer cells

LymphLymph is a milky body fluid that is a milky body fluid that contains a type of white blood cells, contains a type of white blood cells, called called lymphocyteslymphocytes, along with , along with proteins and fats.proteins and fats.

LymphLymph seeps outside the blood seeps outside the blood vessels in spaces of body tissues and vessels in spaces of body tissues and is stored in the is stored in the lymphatic systemlymphatic system to to flow back into the bloodstream. flow back into the bloodstream.

Through the flow of blood in and out of Through the flow of blood in and out of arteries, and into the veins, and through arteries, and into the veins, and through the the lymph nodeslymph nodes and into the and into the lymphlymph, the , the body is able to eliminate the products of body is able to eliminate the products of cellular breakdown and bacterial invasion.cellular breakdown and bacterial invasion.

There are more than There are more than 100 tiny, oval 100 tiny, oval structures calledstructures called lymph nodeslymph nodes. . These are mainly in the neck, groin These are mainly in the neck, groin and armpits, but are scattered all and armpits, but are scattered all along the lymph vessels. along the lymph vessels.

They act as barriers to infection by They act as barriers to infection by filtering out and destroying toxins filtering out and destroying toxins and germs. The largest body of and germs. The largest body of lymphoid tissue in the human body is lymphoid tissue in the human body is the spleen. the spleen.

As the As the lymphlymph flows through lymph flows through lymph vessels, it passes through vessels, it passes through lymph nodeslymph nodes. .

White blood cells called White blood cells called macrophagesmacrophages trap and engulf cell debris and trap and engulf cell debris and pathogenspathogens. Other white blood cells, . Other white blood cells, called called

LymphocytesLymphocytes - - are a type of white are a type of white blood cell capable of producing ablood cell capable of producing a specific immune responsespecific immune response to unique to unique antigens. Theyantigens. They produce produce antibodiesantibodies which are chemicals that mark which are chemicals that mark pathogens for destruction.  pathogens for destruction.  

The scanning electron micrograph above, shows a human macrophage (gray) approaching a chain of Streptococcus pyogenes (yellow). Riding atop the macrophage is a spherical lymphocyte. Both macrophages and lymphocytes can be found near an infection, and the interaction between these cells is important in eliminating infection.

Once a white cell has left the blood vessel and Once a white cell has left the blood vessel and migrated to the enemy, the next job is to EAT migrated to the enemy, the next job is to EAT the microbe.the microbe.

The The macrophage macrophage is a large phagocyte. A is a large phagocyte. A phagocytephagocyte is an eating cell (phago = is an eating cell (phago = "eating", cyte = "cell") which engulfs invaders."eating", cyte = "cell") which engulfs invaders.

Immunity is the result of the action of two types Immunity is the result of the action of two types lymphocytes, thelymphocytes, the B lymphocytesB lymphocytes and theand the T lymphocytesT lymphocytes. .

B cells produce antibodies that are secreted into the B cells produce antibodies that are secreted into the blood and lymph. blood and lymph.

    T cells attack the cells that have antigens that they T cells attack the cells that have antigens that they

recognize.recognize.

Killer T Cells (lymphocytes) recognize surface markers on other cells labeled for destruction. They, Killer T Cells, help to keep virus-infected or malignant cells in check.

Here, a smaller Killer T Cell (arrow) is attacking and killing a much larger flu virus-infected target. The sequence represents 30 minutes elapsed time.

It has been estimated that during our It has been estimated that during our lifetime, we will encounter a million foreign lifetime, we will encounter a million foreign antigens capable of causing disease, and our antigens capable of causing disease, and our bodies need the same amount of bodies need the same amount of lymphocytes to defend against them.lymphocytes to defend against them.    

There will always be aThere will always be a different type of different type of lymphocyte for each possible antigenlymphocyte for each possible antigen. .

•Active Immunity occurs when when one makes his/her own antibodies. This type of immunity is long term.

•Getting the disease : If you get an infectious disease (like Chicken Pox), often times, that stimulates the production of MEMORY cells which are then stored to prevent the infection in the future.

             

       

Vaccination: A vaccination is an injection of a weakened form of the actual antigen that causes the disease. The injection is too weak to make you sick, but your B lymphocytes will recognize the antigen and react as if it were the "real thing". Thus, you produce MEMORY cells for long term immunity.

Passive Immunity occurs when the antibodies come from some other source. This type of immunity is short term.

Breastmilk : Milk from a mother's breast contains antibodies. The baby is acquiring passive immunity. These antibodies will only last several weeks.

                

                         

Gamma Globulin: A Gamma Globulin shot is purely an injection of antibodies to provide temporary immunity. You might receive an Gamma Globulin shot if you travel outside of the country.