INTRODUCTION TO THE IMMUNE SYSTEM



INTRODUCTION TO THE IMMUNE SYSTEM

For thousands of years people believed that diseases were caused by evil spirits, magic, evil deeds (sin), and bad air. People who were sick were often considered cursed, etc.

THE GERM THEORY OF DISEASE- stated that disease is caused by pathogens (disease causing organisms bacteria, viruses, fungi.....-)--developed by Louis Pasteur and Robert Koch

SOME EXCEPTIONS:

1. Many healthy people carry pathogens but do not exhibit the symptoms of disease. Typhoid Mary—19th-20th century…..These “carriers” may transmit the pathogens to others who then may become diseased.

2. Some microbes are very difficult to grow under in-vitro (in the laboratory) conditions. Examples: viruses, Chlamydia, rickettsias, and bacteria that cause leprosy and syphilis. Some of the fastidious organisms can now be grown in cultures of human or animal cells or in small animals-leprosy in armadillos.

3. Not all laboratory animals are susceptible to all pathogens. Many pathogens are species specific. Ethical considerations limit the use of laboratory animals and human volunteers.

4. Certain diseases develop only when an opportunistic pathogen invades a susceptible host. These secondary invaders or opportunists cause disease only when a person is ill or recovering from another disease. For example in case of pneumonia and ear infections following influenza, isolation of bacteria causing pneumonia may mislead the isolation of influenza virus.

5. Not all diseases are caused by microorganisms. Many diseases are caused by dietary deficiencies (scurvy, rickets). Some of the diseases are inherited or are caused by abnormality in chromosomes. Still others such as cancer of the lungs and skin are influenced by environmental factors.

TYPES OF DISEASES

Infectious Only about 1/2 of diseases

Genetic

Wear and tear

Some prime source of pathogens=contaminated water, soil, food, animals

Transmission may be by

(1) direct contact (common cold)

(2) vectors (malaria, Lyme Disease, Bubonic Plague)

(3) object (food poisoning)

(4) airborne

IMMUNITY is RESISTANCE TO DISEASE

(1) Infectious disease-diseases that can be transmitted by infected animals, humans, or objects such as contaminated food, water or objects

(2) Contagious disease-narrower-only diseases spread from person to person

Rabies is infectious (from rabid animal bite) but not contagious

Flu is infectious and contagious-spread

Endemic-disease always present in the population-common cold

Epidemic-occurs when many in same area get disease at same time--flu, typhoid fever, etc.

Pandemic-world wide disease

Treatment (1) Antibiotic bacteria infection= -problem with resistance

(2) Vaccinations-Edward Jenner-=cowpox, smallpox

(3) Interferon-Naturally produced by body to interfere with virus’ ability to reproduce

(4) Chemotherapy/radiation

A FEW WORDS TO KNOW:

IMMUNITY-specific resistance to disease

PATHOGEN-Disease causing organism

ANTIGEN-substance foreign to the body such as bacteria-elicits immune response

ANTIBODY-substance that acts against foreign bodies such as bacteria

THERE ARE 2 DEFENSE MECHANISMS

(1) NONSPECIFIC IMMUNITY- not concerned with what type pathogen or invader attacks the body general defense against anything that the body recognizes as NOT SELF-

Advantage: Meets the enemy as soon as It presents Itself-

NEUTROPHILS, MONOCYTES, MACROPHAGES, NK CELLS

(2) SPECIFIC IMMUNITY-mechanisms that recognize SPECIFIC agents-

Disadvantage: (1) Must be primed

(2) Takes TIME to recognize their target and react with sufficient force to overcome the enemy

NONSPECIFIC DEFENSES:

1st Line of Defense:

MECHANICAL BARRIER:SKIN/MUCOUS MEMBRANES/HAIRS/CILIA

CHEMICAL BARRIER:

(a) skin secretions (acid pH)

(b) HCl protects stomach lining/kills bacteria in stomach

(c) saliva and tears contain LYSOZYME, enzyme that

destroys bacteria

(d) sebum-contains bactericide

(e) mucus-sticks pathogens together--sweep away

When nick or cut breaks the surface barriers, microorganisms infiltrate and then need 2ND LINE OF DEFENSE

2ND LINE OF DEFENSE:NONSPECIFIC DEFENSES---5 PARTS TO THIS

1. INFLAMMATORY RESPONSE-surface barrier is breached by pathogens or tissues are injured by heat, cold, UV radiation or physical trauma

INFLAMMATION

Right after injury brief vasoconstriction, then vasodilation Serotonin-Inhibits neurotransmitters--helps with vasodilation

PUS=mixture of dead or dying neutrophils, broken down tissue cells, and living and dead pathogens

5 Cardinal Signs of Inflammation

(1) Redness=hyperemia=vasodilation=more blood to area, the chemicals that promotes this is HISTAMINE

(2) Swelling (edema)=capillaries become more permeable and fluid seeps out (plasma)

(a) dilutes harmful substances,

(b) brings oxygen and nutrients for repair,

(c) allows clotting proteins in

(3) Pain=caused by swelling pressing on nerve endings

(4) Fever=pyrogens-chemicals causing fever

(5) Impairment of function allows rest and recovery (usually at a joint)

2. PHAGOCYTOSIS

MACROPHAGES AND NEUTROPHILS engulf foreign substances- -destroys the substance/pathogen

1st to ARRIVE: MAIN PHAGOCYTE:Neutrophils=ALSO RELEASE into the surrounding area an oxidizing agent, a chemical (like bleach) which causes thorough killing activity in the area so that the neutrophils as well as the pathogen are destroyed

Phagocytes have a short life span and they pile up at the inflammation site-forming most of the PUS

3. NATURAL KILLER CELLS--NONSPECIFIC

(1) kill cancer and virus infected cells by lysis

(2) attack transplanted tissue/grafts

NKs are a group of LYMPHOCYTES-BUT NOT T OR B (Which ARE SPECIFIC)

NKs act spontaneously against any virus infected or tumor cells- nonspecific-DAMAGE THE CELL MEMBRANES TO LYSE OR BREAK THEM APART

4. ANTIMICROBIAL SUBSTANCES

(1) INTERFERON-produced by virus infected cells- binds to other cells and protects them by interfering with the ability of viruses to reproduce in these cells

(2) COMPLEMENT-about 20 Inactive enzymes In the plasma

when complement is FIXED AND ACTIVATED chemicals are released that magnify the inflammatory response-it "complements" the effectiveness of non-specific and specific response to lyse microorganisms and enhance phagocytosis and inflammatory response

5. FEVER-370C (98.60F) normal-Part of inflammatory response Macrophages release pyrogens (chemicals which raise blood

temperature)

HIGH FEVER= Dangerous-inactivates enzymes

MODERATE FEVER=Benefits:

(1) Speeds up metabolism and defensive actions of body

(2) Liver and spleen sequester iron-makes it less available to bacteria which require a large amount of iron to proliferate

3RD LINE OF DEFENSE: SPECIFIC BODY DEFENSES-IMMUNE RESPONSE

TO BE SPECIFIC IT MUST RECOGNIZE NOT SELF (UNSELF) AGENTS

These experiments revealed three important aspects of immune response:

(1) Antigen specific-recognizes and works against particular

antigens-200 different types of strep-different response to each

(2) Systemic-immunity is not restricted to the initial infection site-

The entire body is protected.

(3) Memory-recognizes and mounts a vigorous attack on previously encountered pathogens.

Thus they discovered 2 TYPES OF SPECIFIC IMMUNITY

(1) ANTIBODY MEDIATED IMMUNITY-provided by the antibodies in the body fluid--produced by lymphocytes-B CELLS

Antibodies bind to bacteria and their toxins and to free viruses inactivating them temporarily and marking them for destruction by phagocytes or complement

(2) CELL-MEDIATED IMMUNITY-provided by NON-ANTIBODY producing lymphocytes T CELLS

1. directly attack invaders and lyse body cells infected by viruses or other intracellular parasites, cancer cells,

foreign grafts

2. release chemicals that enhance the inflammatory response or help to activate lymphocytes or macrophages.

Densest populations of lymphocytes:

1. bone marrow 2. thymus 3. lymph nodes 4. spleen

CELLS OF THE IMMUNE SYSTEM

LYMPHOCYTES:

T or B lymphocyte

INACTIVE B cells-synthesize, but do not secrete antibodies-INSTEAD they insert about 100,000 antibodies on their plasma membranes- the combining sites on these antibodies serve as receptors for their "matching" antigens->leave bone marrow and->lymph nodes, spleen, other lymphoid tissue

SECOND STAGE-occurs when B cell is activated by an encounter with its specific antigen-when the epitopes combine with the antibody combining sites on the surface of the B cell and activate a series of mitotic divisions--- >>>>CLONE of Identical B cells-->some DIFFERENTIATE into PLASMA CELLS which produce antibodies---others do not differentiate and are so-called MEMORY B CELLS--which do not produce antibodies but later if they are exposed to the antigen that triggered their formation, they will become PLASMA CELLS->antibodies

ULTIMATE FUNCTION OF B CELLS IS TO BE THE ANCESTOR OF PLASMA CELLS

The antibodies circulate in the blood or lymph where they bind to antigens and MARK THEM FOR DESTRUCTION BY OTHER SPECIFIC OR NOT SPECIFIC MECHANISMS

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