Immunity The Body Defense

3 Lines of Defense First line - Surface and Mucus Barrier Second Line Physical and Chemical barriers Second Line Inflammatory response and Leukocyte response Third Line – Immune response The purposes of these are to protect your body against Pathogens Pathogens – viruses, bacteria and other microorganisms that cause disease

Surface Barriers (1st Line) Skin The skin cannot be penetrated by most organisms unless it already has an opening, such as a nick, scratch, or cut. Mechanically pathogens are expelled from the lungs by ciliary action as the tiny hairs move in an upward motion; coughing and sneezing abruptly eject both living and nonliving things from the respiratory system the flushing action of tears, saliva, and urine also force out pathogens, as does the sloughing off of skin. Sticky mucus in respiratory and gastrointestinal tracts traps many microorganisms.

Surface Barriers Continued Acid pH (< 7.0) of skin secretions inhibits bacterial growth. Hair follicles secrete sebum that contains lactic acid and fatty acids both of which inhibit the growth of some pathogenic bacteria and fungi. Saliva, tears, nasal secretions, and perspiration contain lysosomes, an enzyme that destroys bacteria. The stomach is a formidable obstacle secreting hydrochloric acid (0.9 < pH < 3.0, very acidic) and protein-digesting enzymes that kill many pathogens. The stomach can even destroy drugs and other chemicals.

Inflammation (2nd Line) Inflammation is characterized by redness and swelling Inflammation is stimulated by chemical factors released from damaged cells. The increased blood flow causes puffiness, warmth, and attracts phagocytes (Neutrophils/Macrophages) Macrophages are giant white blood cells that ingest large numbers of bacteria. As the inflammation response proceeds, the phagocytes ingest the pathogens and any damaged tissue Pus – a mixture of dead WBCs (phagocytes), dead cells, bacteria and body fluid. Pus is either brained or absorbed by the body

Immune System (3rd Line) When the first two systems fail to stop the pathogen the immune system is the last line of defense. The immune system Recognizes the pathogen Attacks Destroys Remembers This is done by creating antibodies and specialized cells that destroy pathogens Unlike the first two lines of defense the immune system is specific for each pathogen

The immune response Immunity – the ability to fight infection through the production of antibodies or cells that inactivate pathogens In order for the immune system to work properly the body needs to be able to recognize SELF from NON-SELF

Antigens Antigen – ANY substance that causes an immune response. Viruses and microorganisms have substances on their outer surfaces that are antigens. Most antigens are proteins. Humans have a unique combination of proteins that no other human has. As a result transplanted tissue will act as an antigen. The job of the immune system is to attack and destroy any antigens.

Lymphocytes Lymphocytes are WBCs that recognize specific antigens and either produce antibodies or kill foreign cells directly. 2 Types of Lymphocytes B lymphocytes – B cells T Lymphocytes – T cells B and T cells are capable of recognizing different antigens B cells mature in the bone marrow T cells mature in the thymus gland

Primary Immune Response When antigens enter your body for the first time your immune system goes through the primary immune response The first 5 days following exposure to the antigen there is no measurable amounts of antibodies or specialized immune cells. Over the next 10-15 days there is a gradual rise in the levels of these products

Secondary Immune Response If an antigen enters the body for second time the response is much more rapid. Within 1 to 2 days after infection of antigen, high levels of antibodies and immune cells are present in blood

B Cells When a B cell comes in contact with an antigen (bacteria) it doesn’t automatically produce antibodies it needs to be stimulated by a helper T cell that recognizes the same antigen that is being displayed by a phagocyte. Following this stimulation the B cell divides into a plasma cell and memory B cells Plasma cell produce antibodies. These antibodies bind to the specific antigen which attracts other phagocytes. Phagocytes engulf and destroy the antigen-antibody complex Plasma cells only last a few days, memory b cells can last a life time (secondary immune response)

Immune control As the antibodies and phagocytes overcome the infection other T – cells help to slow down and stop the plasma cells from producing antibodies These T cells are known as suppressor T- cells This activity of the suppressor T – cells keeps the immune system under control

T Cell When the antigen is a virus - infected cell a single T cell recognizes the antigen the cell surface. Helper T cells recognize the antigen when it is displayed by a phagocyte Helper T cells stimulate the T cells to divide into Killer T cells and Memory T cells Killer T cells bind to the antigens on the viral infected cells and cause the cell to burst. Memory T cells will activate and cause a secondary immune response if the same virus infects the body again

Active Immunity Active immunity: being infected by a live antigen (bacteria/virus) causing a primary immune response. (Memory B and T cells) Active immunity is also developed though a vaccination. Vaccinations consist of dead or weakened bacteria or viruses that cause an immure response but do not make an individual sick. Ex. small pox

Passive Immunity Passive (borrowed) immunity : due to acquiring preformed antibodies from another individual. Example: immunized person gets tetanus shot after stepping on rusty nail. Shot consists of antibodies to the tetanus toxin made in the body of some animal (e.g. horse). Provides immediate protection, but will not last. Passive immunity typically lost after 6 months. Newborn children do not yet have active immunity. For first 6 months, don't get many diseases, protected by mother's antibodies passed to blood system of newborn before birth. After 6 months, infant must rely on its immune system to "learn" and acquire immunity to series of diseases.

Normal Adult Blood Cell Counts Red Blood Cells - 5.0*106/mm3 Platelets - 2.5*105/mm3  Leukocytes - 7.3*103/mm3   Neutrophil 50-70%  Lymphocyte 20-40%  Monocyte 1-6%  Eosinophil 1-3%  Basophil <1%

Antibodies & Antigens Antigens are "foreign" substances that induce some kind of immune response. Antibody or immunoglobulin is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen on the surface of the bacteria or virus

Types of Vaccines Whole microbe vaccines Killed vaccines : heat, formalin, etc. Example: Salk polio vaccine Live vaccines : attenuated strains. An attenuated virus is a weakened, less vigorous virus Example: Sabin polio vaccine. Note: live vaccines generally preferable (one dose vs many), but may cause disease in immunocompromised, so killed vaccines still useful.

Auto-immune diseases The immune system fails to recognize some body cells as self cells. Makes antibodies against self cells and the immune system attacks self-cells. autoimmune diseases: juvenile diabetes – immune system attacks insulin producing cells Multiple sclerosis – immune system attacks the fatty covering of the nerve cells

Allergy Allergy is a rapid overreaction to an antigen that is not normally harmful Allergy common symptoms: Runny nose Swollen, ichy eyes Sneezing, coughing A rash These symptoms are causes by the release of histamine which causes an inflammatory response Antihistamines are used to counter these effects

HIV and AIDS HIV = Human Immunodeficiency virus AIDS = Acquired Immune Deficiency syndrome When HIV enters the body the immune system recognizes it as an antigen and responds but the body defenses are unsuccessful HIV infects Helper T- cells It can stay there for months or years without producing any symptoms When HIV becomes active it reproduces and destroys the helper T- cells. This weakens the immune system and the body cannot fight infections. (HIV  AIDS) HIV can also attacks the nervous system and can cause memory loss, partial paralysis, or mental disorder

How is HIV Spread HIV is primary a sexually transmitted disease ANY intimate sexual contact that involves the exchange of body fluids. (except deep kissing) Blood to blood contact Sharing dirty needles HIV can be transmitted from a mother to an unborn baby

Prevention ABSTINENCE Condoms – help but do not eliminate the chance of getting HIV Not using intravenous drugs Do not come into contact with someone's blood without protective gear.