Immune system

Germ Theory of Disease

• “Microorganisms cause infectious disease”

• Louis Pasteur and Robert Koch did several experiments to identify disease causing agents.

• Determined that each disease is caused by a “specific” microorganism

Agents of Disease

• The following types of organisms can cause disease:1. Viruses2. Bacteria3. Protists (malaria)4. Worms 5. Fungi

• Pathogen is anything that causes disease.

Koch’s Postulates

• In order to identify what organism causes a specific disease, certain rules are followed.

• Koch Postulates:1) pathogen must be found in subject with

disease but never in a healthy subject2) pathogen can be isolated from sick person

and grown in lab3) pathogens injected into healthy person will cause the individual to become infected with the same disease4) injected pathogens can be isolated from

newly infected individual and are identical to original pathogens

Koch’s Experiment- Germ Theory

• Koch’s postulates are very important because they are the basic steps for identifying, curing, and preventing specific diseases.

What is a system?

• A group of tissues (organs) work together to do a task.

• Ex) digestive system, circulatory system, immune system…

• Function of the immune system is to protect body from invasion by pathogens.

Overview of Body’s Defenses

Non-Specific Defenses Specific Defenses

First Line of Defense Second Line of Defense

Immune Response

Skin and Mucous Inflammatory ResponseNon-SpecificWBC (phagocytes)

Specific (diverse)Antigens/AntibodiesLots WBC Memory

Non-Specific Defense• Similar to “walls of a fort” protect by keeping

pathogens out of body• Body does NOT distinguish one pathogen from

another• Your body has several non-specific defenses…

1) External- skin and mucous membranes (1st line defense)

2) Internal- Inflammatory response (2nd line defense)

“Skin”

• Physical barrier• Chemical barrier-

secretes oil and sweat (lowers pH skin), tears (contain enzyme called lysozyme), and saliva

• Sheds constantly (1 million cells per hour)

“Mucous Membranes”

• Skin contains natural openings (nose, mouth, trachea, esophagus)

• These areas are lined by mucous membranes

• Secrete mucus traps foreign objects

• Areas lined with cilia• Any pathogens make it

past, may be killed by stomach acids.

“Small Scale Infections”

• The first line of defense has been broken… second line of defense is triggered to attack any invaders present

• Inflammatory response • Body’s attempt to destroy pathogens that enter the body when the skin

is injured• Triggers series of reactions …

1.) Chemical called histamine is released from white blood cells called basophils

2) Blood vessels in area of injury swell 3) Tissue at injury site swells4) Temperature in area of injury rises = redness5) White blood cells called phagocytes move from the vessels into the injured tissue eat pathogen and damaged skin cells6) Platelets clot blood and seal infected area

“What if pathogens get in?”

• White blood cells take over and specifically identify and eliminate the pathogen.

• White blood cells = “soldiers” • Immune Response

Organs of the Immune System

White blood cells called leukocytesMade thymus and bone marrowStored tonsils, spleen, and lymph nodes.

How does your body know

there is an invader?• All pathogens have “distinct” antigens.• Antigens are marker proteins- trigger immune

response• Your body must recognize antigens in order to

identify and defeat the pathogen. • Normal cells also have antigens.

Antigen

Antibodies • Your white blood cells produce antibodies in

response to specific antigens. • These are specific to each pathogen.• All pathogens are unique, your immune system

has to prepare a specific defense against each invader.

• If you makes/have the antibodies it can kill the pathogen and you can fight the infection.

• B-cells (type of white blood cell) make the antibodies!

Building “Immunity”

• What happens if a pathogen makes it past the first lines of defense and avoids the inflammation response?

• Your body must “actively” fight the disease.

• This takes time.• This requires a special group of white

blood cells lymphocytes.

“The Soldiers”

• Many types of WBC work together during the immune response to fight the infection.

• Macrophages• Lymphocytes

“The Soldiers”

• 3 major classes of lymphocytes:

1) B-cells (plasma cells)2) T-cells

-Helper T cells -Killer T cells-Suppressor T cells

3) Memory cells

Step #1 “Invader Identification”

• Macrophages identify pathogen, eat it, display antigens, signal helper T cells (interleukin-1).

• Body temperature will increase (interleukin-1) in attempt to slow down pathogen.

• Helper T cells release interleukin 2 – signals help other leukocytes (other T-cells and B-cells)

Step #2 “Cloning Phase”

• B cells make antibodies - lock onto antigens.“Marked for death.”

Antibodies

Antigen

• Killer T cells kill infected body cells.

Step #3 “The Attack Phase”

Step #3 “The Attack Phase”

• Macrophages clean up- eating pathogens, damaged body cells, etc.

• Suppressor T cells “call off the troops” stopping the immune response.

Step #4 “Memory Phase”

• Memory cells “remember” the attack and recognize a pathogen if it re-enters body.

• Primary vs. secondary immune response

Active vs. Passive Immunity

• Active = your body must fight off the disease to build up antibodies. Ex.) Fighting an infection or Vaccination

• Passive = receiving antibodies from an outside source. Ex.) Breast feeding

Other Topics – Related to Immune System

•It is the job of the immune system to distinguish between the body’s own molecules and foreign molecules•Antigens – “marker proteins”•Blood Transfusions and Organ Transplants

If the key fits the lock = bad!!!

Blood Transfusions and the Immune System

• Blood cells have marker proteins or “antigens”

Organ Transplants and the Immune System

• Foreign organs also have marker proteins.

• If recognized as “foreign” = REJECTION.• Doctors must “match” a new organs

marker proteins to the patients.• Drugs can help suppress the immune

response (immunosuppresants).

What if the immune system fails?

• Sometimes the immune system loses the ability to distinguish itself from non-self.

• Results in autoimmune disease• Body attacks own tissues• Ex) lupus, multiple sclerosis, arthritis

LUPUS

• Person’s immune system attacks various organs or cells of the body (skin, joints, kidneys, heart, and lungs) causing damage

• Lupus is a multi-system disease because it can affect many different tissues and organs in the body.

LUPUS

Symptoms:• Fatigue • Low-grade fever, rarely exceeding 102°F• Muscle pain and joint pain or swelling• Skin rash (face, back, arms) and hair loss • Kidney problems and weight loss

Multiple Sclerosis• Immune system attacks mylein around nerve cells• Symptoms: loss ability to walk and move,

loss bladder control, paralysis and death

What if the immune system fails?

• Sometimes the immune system collapses • Ex) HIV • Virus invades macrophages and helper T

cells • Without these WBC immune response

will not work• Body becomes overwhelmed with

pathogens (HIV AIDS)

What if the immune system fails?

• Sometimes the immune system overreacts thinking something is a pathogen when it is NOT

• Allergy- immune system response to a non-pathogenic antigen

• Ex) pollen, food, insect bite, dust, etc.

Steps – Allergic Reaction

• 1) Pollen inhaled• 2) cells of nasal passage

called mast cells release chemical-histamine

• 3) nearby capillaries swell- increases fluid

*Allergies are treated with medication that contains antihistamines (chemical that blocks histamine)

Immune System and Cancer

• Major function of immune system is to patrol for cancer cells

• Called Immunological Surveillance• Killer-T cells can identify, attack, and

destroy cancer cells