Immune System• An animal must defend itself against

unwelcome intruders - the many potentially dangerous viruses, bacteria, and other pathogens it encounters in the air, in food, and in water.

• White Blood cells function as part of the immune system. There are many types of WBC’s- (also called leukocytes)- including lymphocytes, monocytes, neutrophils.

Non-specific Defense Mechanisms

Non-specific

Defense Mechanisms

Specific Defense Mechanisms

(Immune Response)

1st Line of Defense

2nd Line of Defense 3rd Line of Defense

1. Skin

2. Mucous membranes

3. Secretions of Skin and Mucous membranes

1. Phagocytic white blood cells

2. Antimicrobial proteins

3. Inflammatory response

1. WBC’s (Lymphocytes)

2. Antibodies

1st line of Defense

• An organism invading our body must first pass the first line of defense- the skin and mucuous membranes and their secretions– Tears, saliva, sweat

– All secretions contain antimicrobial proteins

– The enzyme, lysozyme, digests cell walls of many bacteria, destroying them.

– Mucous traps and destroys many organisms

– Stomach acids kill many organisms in foods

2nd Line of Defense-

Phagocytosis

• White Blood cells- phagocytize microbes– Neutrophils (60% of WBC’s) engulf microbes

– Monocytes (5% of WBC’s) attach to polysaccharides on microbe’s surface, engulf, and put microbe into lysosome with lysozyme.

• Lysozyme is an enzyme, found in the lysosome of cells, that digests microbial components.

2nd Line of Defense- Inflammatory Response

• Cause: Triggered by damage to tissue by a physical injury or by the entry of microorganisms

• Steps in Inflammatory Response1. Damaged cells or bacteria release chemical signals that cause nearby capillaries to dilate and become more permeable, leading to clot formation at the injury.2. Increased local blood supply leads to the characteristic swelling, redness, and heat of inflammation.

Inflammatory Response3. Phagocytic white blood cells (neutrophils and monocytes) leave

blood and arrive at the site of invasion. “The neutrophilic polymorphonuclear leukocyte (practice saying that phrase!) is the

bacteria bomb. They're very active cells, so they migrate into an infected site very quickly and start chowing down. Major component of inflammation and pus formation. They're full of really high activity lysosomes. When they eat bacteria, activation of those lysosomes is so intense that the bacteria are quickly killed and the whole leukocyte is also killed. Doesn't matter--the bone marrow makes more of these guys every day, so they're essentially suicide cells for rapid attack against bacterial infections. The monocytes/macrophages are larger and slower white cells that come in later and clean up the mess.”Karl J. Aufderheide, Associate Professor, Texas A&M University

4. Pus accumulates at the site of some infections. It consists mostly of dead phagocytic cells and the fluid and proteins that leaked from capillaries during the inflammatory response. (It is eventually re-absorbed by the body.)

5. Increase in WBC’s and development of fever occurs in some severe infections. Fever raises the body temperature and inhibits the growth of some microorganisms.

Inflammatory Response

1. Localized response is triggered with chemical release2. Capillaries dilate, increase blood flow and permeability. 3. Phagocytes and lymphocytes are attracted.4. Phagocytes consume pathogens and cell debris, and tissue

heals

Antigen

• A foreign molecule that illicits a lymphocyte response

• Usually a foreign protein

• Foreign = non-self

• Antigens include molecules belonging to viruses, bacteria, fungi, protozoa, parasitic worms, and nonpathogens like pollen and transplanted tissue

Antibodies

• Produced by plasma cells (a type of WBC) in response to a specific antigen

• Antibodies are specific

• Antibodies are proteins

• Antibodies attack antigens

Lymphocytes- a type of WBC• Lymphocytes form in the bone marrow. • Some migrate to mature in the thymus gland-

they become lymphocytic T cells.• Those that stay and mature in the bone marrow

become lymphocytic B cells.• Mature lymphocytes circulate throughout the

blood and lymph.• B cells and T cells specialize in different types

of antigens, and they carry out different, but complementary, defensive actions.

Functions of lymphocytes

• B Lymphocytes (B cells)-• produce plasma cells which produce antibodies• Produce memory cells

• T Lymphocytes (T cells) • Helper T cells- identify foreign cells and stimulate B

lymphocytes

• Suppressor T cells- stop activities of B and T cells once infection has passed

• Killer T cells- kill cancer cells, kill body cells that have been invaded, responsible for “rejection” of transplanted tissues

The Lymphatic Systemwith bone marrow & thymus gland

Primary Immune Response

• Primary Immune Response– First encounter with a foreign antigen– Usually takes 10-17 days for maximum

response– Lymphocytic B cells produce

• Plasma cells that secrete antibodies• Memory cells for the specific antigen

– More T cells are produced, which directly attack the antigen

Production of Plasma and Memory Cells from B cells

Secondary Immune Response

• Secondary Immune Response– Takes only 2-7 days for maximum response– Memory cells are already available; they make

plasma cells that produce the specific antibody– Response is quicker, more prolonged and more

intense.

Immune Response

Self/ Non-self• It is important for your immune system to

distinguish self from non-self.• There are sets of glycoproteins located on

the surface of most of our cells that identify these cells as “self”.

• Only identical twins have identical glycoproteins

• Failure to identify “self-cells” can lead to auto-immune diseases

Blood Transfusions and Transplants

• Matching antigens prior to blood transfusions and transplants is essential.

• Foreign proteins/antigens can cause an immune response.

• Incorrect blood types- result in clotting and death of recipient

• “Rejection” of transplants, can cause the transplant to fail.

• Cyclosporine is a drug that decreases immune response- often administered to transplant recipients.

Active Immunity• Active immunity- caused by acquiring memory cells

– Natural- by exposure to an antigen – Artificial- by immunization or vaccination

• Vaccines include inactivated toxins, killed microbes, parts of microbes, and viable but weakened microbes.

• These no longer cause disease, but they can act as antigens, stimulating an immune response, and more important, immunological memory.

• First vaccination- Edward Jenner- against smallpox

• Louis Pasteur- vaccines for anthrax, rabies, cholera

• Polio vaccine: 1950’s Salk- injected; Later, Sabin- oral

Passive Immunity

• Passive immunity- antibodies transferred from one individual to another

• Passive immunity persists as long as these antibodies last, a few weeks to a few months– antibodies of a pregnant woman cross the

placenta to her fetus– antibodies are passed from mother to nursing

infant in breast milk

Allergies

• Allergies are hypersensitive (exaggerated) responses to certain environmental antigens, called allergens.

• Antibodies may attach to mast cells in connective tissues- not to the antigen (i.e. pollen)

• Later exposure to the antigen, causes the antigen (pollen) to attach to the mast cell.

• This triggers the mast cells to release histamines.

Allergies-2

• High levels of histamines cause dilation and increased permeability of small blood vessels.– These inflammatory events lead to typical

allergy symptoms: sneezing, runny nose, tearing eyes, and smooth muscle contractions that can result in breathing difficulty.

– Antihistamines diminish allergy symptoms by blocking receptors for histamine.

Autoimmune Diseases• Cause- when the immune system loses tolerance for

self and turns against certain molecules of the body.• Systemic lupus erythematosus (lupus),

characterized by skin rashes, fever, arthritis, and kidney dysfunction

• Rheumatoid arthritis leads to damage and painful inflammation of the cartilage and bone of joints

• Insulin-dependent diabetes mellitus, the insulin-producing beta cells of the pancreas are the targets of autoimmune cell-mediated responses

• Multiple sclerosis (MS), T cells reactive against myelin, infiltrate the central nervous system and destroy the myelin of neurons.

Acquired immunodeficiency syndrome, or AIDS.

• With the AIDS mortality close to 100%, HIV is the most lethal pathogen ever encountered.

• After an initial peak, virus levels in the blood fall as anti-HIV antibodies, produced 1 to 12 months after infection, rise.

• After the early drop in HIV levels in the blood, the virus continues to be produced by cells in the lymph nodes, causing structural and functional damage.

AIDS• The time required for an HIV infection to progress

from severe helper T cell depletion to AIDS varies greatly, but it currently averages about ten years.

• At this time, HIV infection cannot be cured, and the progression to AIDS cannot be prevented.

• New, expensive drug therapies can slow this progression.

• Transmission of HIV requires the transfer of body fluids containing infected cells, such as semen or blood, from person to person.

• As of 2000 the Joint United Nations Program on AIDS estimates that 30 to 40 million people worldwide are living with HIV or HIV/AIDS.