Immunity

The Body Defense

3 Lines of Defense

• First line - Surface and Mucus Barrier– 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 or Mucosal Immunity (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.

Primary Defense

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 Gram positive bacteria causing cell lysis (death).

• The stomach is a formidable obstacle secreting HCl (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. – Developed from monocytes– 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 drained 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 the 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

T- Lymphocyte

Primary Immune Response

• When a antigen enters 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 a memory B cells– Plasma cell produce antibodies. – These antibodies bind to the specific antigens 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)

Phagocytosis of antigen

Macrophage and E Coli

Plasma (B-cell) Making antibodies

Complement System

• When the antigen is a bacterium the complement system helps destroy the bacterium

• Complement System – is a a series of enzymes in the blood that catalyze reactions that result in the bursting of the bacterial cell

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 on 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

Phagocyte engulfs and displays antigen

Killer T - Cell

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 vaccination

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, and from BREAST MILK. After 6 months, infant must rely on its immune system to "learn" and acquire immunity to series of diseases. (unless still being breast fed)

Vaccination against polio

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

• Antibodies = gamma globulins = immunoglobulins, all synonymous terms.

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.

autoimmune diseases

• The immune system fails to recognize some body cells as self. 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 caused 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 also attacks the nervous system and can cause memory loss, partial paralysis, or mental disorder

HIV

How is HIV Spread

• HIV is primarily 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.