I MMUNE S YSTEM Chapter 24. T HE K ISSING D ISEASE The Epstein-Barr virus (EBV) is one of the most common human viruses During childhood symptoms are.

IMMUNE SYSTEMChapter 24

THE KISSING DISEASE

The Epstein-Barr virus (EBV) is one of the most common human viruses During childhood symptoms are mild and often

unnoticeable, but causes mononucleosis or mono in newly infected teens and adults

No vaccine to prevent or an effective treatment Antibiotics are ineffective against viruses

Can only get once because the body develops immunity to it Recognizes and fights pathogens, infectious agents

that cause disease Acquired immunity backs up innate immunity to

form an immune system which limits infections in animals

INNATE IMMUNITY First line of defense

against potential invaders Respond the same

whether invader is novel or not

Invertebrates Sole defense is

external and internal barriers Exoskeleton,

lysozymes to digest cell walls, immune cells to phagocytize foreign invaders, and recognition proteins

Vertebrates Coexists with acquired

immunity

VERTEBRATE DEFENSES

External to prevent Skin and mucus membranes protect systems

exposed to external environments E.g. nostril hairs to filter particles from the air and

respiratory tract mucus to trap those it misses, and cilia to move them up and out

Internal fight after infection occurs WBC’s found in interstitial fluid and blood vessels

E.g. neutrophils and macrophages phagocytic and wander interstitial fluid ‘eating’ bacteria; natural killer cells release chemicals to promote cell death

COMPLEMENT PROTEIN SYSTEM

Enhances innate immune responses About 30 different proteins present in an

inactive form in the blood at all times Activated by surface receptors of microbes which

creates a trigger cascade to activate other proteins

Leads to lysing of invaders Some help trigger inflammation response

INFLAMMATORY RESPONSE Triggered by any damage to a tissue

From microorganisms to insect bites and scratches Seen with improperly treated cuts, also responsible

for sore throats Triggering the response

Damaged cells release a chemical signal such as histamine Induces nearby blood vessels to dilate and leak

Blood flow to the area increases producing the redness, heat, and swelling

Other chemicals attract phagocytes Purpose to disinfect and clean injured tissue

Engulf bacteria, damaged or dead body cells, and dead WBC’s Pus is dead WBC’s and fluid from leaking capillaries

Prevents spreading of infection via clotting proteins and platelets

TAKING INFLAMMATION ON THE ROAD

Inflammation response can be local, as just described, or widespread (systemic)

Once entering the bloodstream, microbes can be carried throughout the body

Several responses occur Elevated WBC count is one indicator Fever or abnormally high body temperature

Triggered by toxins or macrophages and can stimulate phagocytosis and speed tissue repair

Septic shock, an overwhelming inflammatory response Very high fever and low blood pressure Common cause of death in critical care hospital units

LYMPHATIC SYSTEM

Involved in innate and acquired immunity Includes numerous structures, vessels, and cells Circulates lymph which is similar to interstitial

fluid, but with less O2 and fewer nutrients Main functions:

Return tissue fluid to circulatory system Lymph drains to veins in chest Vessels have valves to prevent backflow and depend mainly

on skeletal muscles to move fluid (like veins) Fight infections

Carries invaders to lymphatic organs to be engulfed by permanent macrophage residents (innate of acquired response)

Cause lymph nodes to swell from number of cells

ACQUIRED IMMUNITY

Second line of defense for when innate response fails

Only in vertebrates and is active only AFTER exposure to pathogens Varies between individuals depending on

exposure Highly specific defense so acts against only 1

agent Can amplify innate responses like

inflammation and the complement system Obtained by natural exposure or through

vaccinations

FIGHTING THE INVADERS

Antigens are the foreign molecules responsible for eliciting these responses Molecules from pathogens or other particles such as

viruses, bacteria, mold spores, or transplanted organs Body remembers antigens previously exposed to Body responds to antigen presence by:

Increasing cells to attack the invader Producing immune proteins called antibodies which

attach to specific antigens to counter its’ effects Response is usually quick enough to attack and

destroy before symptoms occur; its adaptive Exposure enhances future responses to the same

agent

VACCINATIONS Exposure to harmless variants, inactivated

toxins, or dead/weakened microbes to stimulate the immune system

Almost eliminated numerous viral diseases E.g. polio, smallpox, mumps and measles

Resulting immunity from antigen exposure, naturally or artificially, is active immunity Body actively produces antibodies

Receiving premade antibodies is passive immunity When travelers go to foreign countries or treatment

of a snakebite with antivenom Temporary results because body isn’t stimulated by

antigens, the immunity ends once antibodies are gone

LYMPHOCYTES

WBC’s that reside in tissues and organs of the lymphatic system

Responsible for acquired immune responses Originate from stem cells in bone marrow

Remain and become B cells Move to the thymus and become T cells Both eventually to spleen and other organs

Work to form a dual defense Humoral immune response Cell-mediated immune response

IMMUNE RESPONSE TYPES

Secretion of B cells into blood and lymph

Defends against bacteria and viruses in body fluids (outside cells)

Passively transferred via blood plasma containing antibodies from immune to nonimmune individuals

Defensive proteins responsible

Produced by T cells Attack body cells

infected with bacteria or viruses

Promote phagocytosis by other WBC’s

Stimulating B cells to make antibodies

Defensive cells responsible

Humoral Cell-Mediated

PRODUCTION OF B CELLS AND T CELLS Certain genes are

turned on in developing cells

Synthesizes proteins to be incorporated onto the PM called antigen receptors which bind specific antigens

All receptors on a single cell are identical B cells to the

particular antibody it produces

ANTIGEN AND ANTIBODY BINDING

Antigens don’t usually belong to the host animal Proteins or polysaccharides on foreign cell

surfaces E.g parts of capsules, bacterial cell walls, and

macromolecules on the surface of other organisms

Antibodies bind to an antigenic determinant or epitope of an antigen Complementary shapes on both facilitate it

Antigens possess several determinants so multiple antibodies can bind Single antigens can stimulate production of

multiple types of antibodies

HUMORAL RESPONSE WEAPONS B cells secrete antibodies

(proteins) Made of 2 heavy chains and 2

light chains Functions to:

Recognize and bind certain antigens (light chains)

Assist in neutralizing the antigen it recognizes (heavy chains)

Antigen-binding site varies in shape to enable it to react to any antigen

Tail for disposal and groups them into 1 of 5 major classes of antibodies Differ in body location and function

ELIMINATING ANTIGENS Antibodies must be able to mark invaders

Form an antigen-antibody complex held by weak bonds Actual binding of antibodies trigger destruction called

effector mechanisms Specific recognition-and-attack phase followed by a

nonspecific destruction phase

Blocks viral binding sites

Group cells

Group dissolved molecules

Attach andpoke holes inthe PM=lysis

T CELL TYPES

Respond to antigens on cell surfaces = infection inside cells

Cytoxic T cells attack body cells infected with pathogens

Helper T cell roles are multifaceted, and interact with WBC’s that function as antigen-presenting cells Interaction activates helper T cells to activate

other cells of immune system

o Macrophage ingests a microbeo Self-proteins bind microbe pieces = nonself moleculeso Helper T recognizes self-nonself complex

o Has 2 binding sites

oActivates Helper T which promotes the immune response

Activating Helper T Cells

o Only T cells that actually kill infected cellso Identify infected cells like Helper T cellso Binding activates so new proteins produced

o Produce holes in cell membrane

o Enzymes enter to promote apoptosis

Cytotoxic T Cells

ALLERGIES

Hypersensitive responses to antigens in our surroundings Allergens are antigens that cause allergies

Feces of tiny mites in dust and animal dander (shed skin cells)

Bed Bugs (Cimex lectularius)

Dog/cat allergies commonly to saliva proteins deposited on fur

Symptoms from 2 stage reaction Sensitization Allergic response

Reactions can vary Anaphylactic shock when allergens make mast cells

release inflammatory chemicals suddenly Blood vessels dilate so blood pressure drops rapidly Epinephrine injections can counter

ALLERGIC REACTIONS

Allergen enters bloodstream and binds B cells B cells proliferate and secrete lots of antibodies

Attach to mast cells which produce histamine for inflammatory response

Allergen enters body and bind to antibodies on mast cells

Releases histamine to trigger symptoms Antihistamines interfere with and so provide relief