The Immune System(Chapter 15)

The Immune System

• Immunity is the ability to react to antigens so that the body remains free of disease.– Disease is a state of homeostatic imbalance.

• Can be due to infection or failure of the immune system.

Primary Lymphatic Organs

• Lymphatic organs contain large numbers of lymphocytes (White Blood cells).

• Primary organs are:-– Red Bone Marrow.

• Site of stem cells.– Source of B lymphocytes.

– Thymus Gland. Lymphocytes from bone marrow pass through to form T-lymphocytes

• Produces thymic hormones (thymosin).

• Aids in T lymphocyte maturation.

Secondary Lymphatic Organs

• Secondary lymphatic organs are places where lymphocytes encounter and bind with antigens.– Spleen.– Lymph nodes.– Tonsils.– Peyer’s patches.

Lymphatic Organs

Secondary Lymphatic Organs

• Spleen – upper left of abdominal cavity behind stomach. Sectioned off by connective tissue- white pulp & red pulp.

– White pulp – lymphocytes

– Red pulp – filters blood. Blood entering the spleen passes through red pulp before it leaves (network of sinuses)

– FRAGILE

Secondary Lymphatic Organs• Lymph Nodes – occur along

lymphatic vessels. Formed from connective tissue.

– Packed full of B-lymphocytes

– As lymph courses through sinuses it is filtered by macrophages, which engulf pathogens and debris.

– Also present- T-lymphocytes – fight infection and attack cancer cells

Secondary Lymphatic Organs• Tonsils – patches of

lymphatic tissue. • Perform the same function

as lymph nodes– First line of defense

• Peyer’s Patches – on the intestinal wall and appendix. Attack pathogens that ender the body by way of the intestinal tract.

Nonspecific Defenses• Barriers to Entry.

– Mucous membranes • Line respiratory, digestive, and urinary tract.

– Oil gland secretions.• Chemicals that kill or weaken bacteria on skin

– Ciliated cells.• Sweep mucus & particles into throat

– Bacteria• Both in stomach and vagina, prevent pathogens

from gaining a foot-hold.

– Acid

Innate Immunity• One important function of the immune system is to promote

growth and repair after injury– Either via physical damage or microorganisms

• The mobilization of innate immune cells to get rid of damaged cells or microorganisms is called inflammation

• Small molecules called cytokines are also involved

Innate Immunity• Inflammatory Reaction.

– Tissue damage causes – tissue cells and mast cells to release chemical mediators.

Innate Immunity• Inflammatory Reaction.

• Histamine and kinins.– Capillaries dilate and become more permeable.

» Skin reddens and becomes warm.– Proteins and fluids escape from tissue. Swelling occurs

Innate Immunity

• Inflammatory Reaction.– Proteins and fluids escape from tissue and cause swelling.

» Swelling stimulates free nerve endings, causing the sensation of pain.

Innate Immunity– Neutrophils and

Monocytes migrate to site of injury.

– Amoeboid – can change shape – squeeze through capillary walls and enter tissue fluid.

– Neutrophils engulf pathogens –destroyed by hydrolytic enzymes when fused to a lysosome

Innate Immunity• Macrophages:

Monocytes change into these as they leave the blood and enter the tissues.– These are phagocytic cells– Can eat many (100’s) of

pathogens and survive.– Eat old blood cells and bits

of dead tissue– Stimulate the immune

response.• Increase production of white

blood cells in bone marrow

Innate Immunity• Macrophages:

Monocytes change into these as they leave the blood and enter the tissues.

• Macrophages enter lymph vessels carring bacteria fragments to lymph nodes

• This starts a specific immune response

Protective protein system• Known as Complement proteins

• Are activated when pathogens enter the body.• Complement certain immune responses.

Protective protein system• Attract phagocytes.

• Form holes in bacteria.• Interferon binds to receptors of non-infected cells causing them to prepare for possible attack

Specific immunity• Antigen--shape on cell, allows recognition of self

and detection of foreign cells.• Antibody--protein that recognizes and binds

antigens.

• Specific defenses respond to antigens.– Lymphocytes recognize an antigen due to antigen

receptors whose shape allows them to combine with a specific antigen.

• Immunity is primarily the result of the action of B lymphocytes and T lymphocytes.

White blood cells• Granular Leukocytes

– Neutrophils: Most abundant. Have multilobed nucleus.• They are the first to respond to infection, and engulf pathogens

during phagocytosis.

– Eosinophils: Have bilobed nucleus• Known to increase in number in the event of parasitic worm

infection and during allergic reaction.

– Basophils: U-shaped or lobed nucleus.• In connective tissues release histamines along with Mast Cells

White Blood Cells • Agranular Leukocyles

– Monocyles: Largest of the white blood cells.• Differentiate into even larger Macrophages

• Phagocytize pathogens, old cells and debris

• Stimulate production of other white blood cells

– Lymphocytes: Two types:• T-lymphocytes – Destroy any cell with foreign antigens

• B-lymphocytes – Produce antibodies that combine with antigens

–Target pathogens for destruction

Natural Killer Cells• Natural killer cells kill

virus-infected cells and tumor cells by cell-to-cell contact.– Large, granular

lymphocytes.

T Cells

• Provide cell-mediated immunity.

• Produced in bone marrow, mature in thymus.

• Antigen must be presented in groove of HLA molecule.

• Cytotoxic T cells destroy non-self protein-bearing cells.

• Helper T cells secrete cytokines that control the immune response.

B Cells• Provide antibody-mediated immunity against

bacteria.

• Produced and mature in bone marrow.

• Reside in spleen and lymph nodes.– Circulate in blood and lymph.

• Directly recognize antigen and then undergo clonal selection.

• Clonal expansion produces antibody-secreting plasma cells and memory B cells.

Clonal selection Theory• The antigen selects which

lymphocyte will undergo clonal expansion and produce more lymphocytes with the same type of antigen receptor.– Some become memory

cells – long term immunity to the same infection.

– B-cells become plasma cells – fight infection

– Apoptosis – when danger of infection is over, all plasma cells undergo programmed cell death

Specific Defenses– Antibodies are proteins

shaped like an antigen receptor and capable of combining with, and neutralizing, a specific antigen.

Antibodies• Classes.

– IgG - Enhances phagocytosis.– IgM - Activates complement proteins.– IgA - Prevents attachment of pathogens.– IgD - Antigen receptors on virgin B cells.– IgE - Immediate allergic response.

Induced Immunity• Active Immunity.

– Immunization involves use of vaccines.

– Contain an antigen to which the immune system responds.

– Primary response. Secondary (booster) response.

– Dependent upon the presence of memory B and T cells capable of responding to lower antigen doses.

Induced Immunity• Passive immunity

• occurs when an individual is given prepared antibodies.

– Temporary.• No memory cells.• Primary and

secondary injections

Issue - Allergies• Occurs when your immune system reacts atypically to some

antigens to which the host does not need protection.

• Pollen, dust mites, cats, a hard days work!– Called Allergens

• The atypical response produces a special antibody– IgE

• A form of innate immunity

Allergies• IgE binds to mast cells.

• When a person later encounters the same allergen, the allergen binds to the IgE on the mast cell

• This triggers the explosive release of histamine

• Capillaries dilate and become more permeable.

• Skin reddens and becomes warm. Proteins and fluids escape from tissue. Swelling occurs

–

Allergies

• The large amounts of histamines released in an allergic reaction cause strong symptoms

• Runny eyes, sneezing, or shortness of breath

• Depends upon the tissue in which the mast cells were triggered

Allergies• As allergy symptoms are caused by histamines, taking

antihistamines stops the build up of histamines in the cells of blood vessels.

• However, antihistamines do not stop the immune response or the release of histamines in mast cells

• Other allergies are mediated by T-cells– Latex, poison ivy, dyes or chemicals in cosmetics or clothing

– Antihistamines do not help in these allergic reactions

Allergies• As each allergy is an antigen-specific immune response it

shows memory and a greater response on the next exposure– This is why allergies get worse over time

• Thousands of different substances can produce allergies in people – each triggered by a specific antigen-specific response– Why people are usually bothered by only a few

• Appears to be inherited– Remember human genetics and meiosis!!!!

The End.

Any Questions?