The Immune System

Nonspecific Body Defenses

Responds immediately Intact skin Mucous membranes Inflammatory Response Cellular Chemicals

Surface Protectors

Skin, Mucous membranes Physical barrier Chemical barrier

pH of skin; pH of vagina; sebum Stomach acid/enzymes Saliva/lacrimal fluids (lysozyme) Sticky mucus to trap invaders in digestive/respiratory

passages

Cells and Chemicals

Phagocytes Macrophages and Neutrophils

Engulf foreign invaders Natural Killer Cells (NK) to “police” body

Kill cancer cells, virus-infected cells NOT phagocytes (think chemical warfare)

Inflammatory Response

Nonspecific response Cardinal Signs

Redness Heat (inflamm… “set on fire”) Swelling Pain

Inflammatory Response

Chemical “alarm” Damaged cells release histamine, kinins

Causes blood vessels to dilate, leaky capillaries Activates pain receptors Attracts phagocytes (WBC’s) to injured area

Called Chemotaxis (cells follow chemical signal)

Redness/heat from increased blood flow Also causes edema (swelling)

Inflammatory Response

Prevents spread of damaging agents to other areas

Disposes of cell debris and pathogens Begins repair process

Chemicals

Complement Group of plasma proteins that circulate (inactive)

Attach to foreign cells and puts holes in the cells Foreign cells die

Amplifies inflammatory response Calls more phagocytes to area

Cause CM’s of foreign cells to stick together

Chemicals

Interferon Small proteins secreted by infected cells

Attach to non-infected cells Slows down virus multiplication

Fever

Abnormally high body temperature Pyrogens increase “thermostat”

Chemicals secreted by WBC’s that have been exposed to foreign cells

Mild-moderate fever helpful in speeding up repair processes in tissues

Immune Response

Recognizes antigens and acts to inactivate or destroy them

Antigen specific Acts against particular pathogens

Systemic Not restricted to infection site

Has a “memory” Recognizes and mounts stronger attacks on

previously encountered pathogens

Antigens

Substance that excites the immune system and provokes an immune response

Foreign intruders are “non-self” Proteins Carbs; some lipids Nucleic acids

Self-antigens don’t trigger immune response but do in other people Explains rejection of transplanted organs

Haptens

An incomplete antigen A small (non-antigenic molecule) When it links up with the body’s proteins, body

thinks it’s foreign These are what cause allergies!

Lymphocytes B and T cells B cells

Mature in bone marrow Produce antibodies (Y-shaped) Oversee humoral immunity

Antibody-mediated immunity T cells

Mature in Thymus gland Help with cell-mediated response (don’t make antibodies)

Immunocompetent When cells can respond to a specific antigen by binding to it

Lymphocytes, cont.

Immunocompetent cells only recognize one antigen All receptors on the cell are the same

Our genes determine what ‘germs’ we can recognize and resist

When cells are immunocompetent, they travel to lymph nodes/spleen to mature

Mature cells circulate the body in search of antigens

Macrophages

“Big Eaters” Antigen presenters

They engulf foreign particles and ‘present’ them like flags so T cells can recognize the antigens

Secretes proteins called monokines Become “Killer Macrophages” in response to

T-cell activation Stay in lymph organs

Humoral (Antibody-Mediated) Immunity

Immature B cell is stimulated to mature when an antigen binds to its surface receptors

Clonal selection begins B cell grows, multiplies to form an army of cloned

cells Most of these become plasma cells

Antibody-producing factories (produce 2,000 per second)

Humoral (Antibody-Mediated) Immunity

B cell clones that don’t become plasma cells become memory cells Can respond to the antigen later Provide secondary response

Faster and more effective, because attack plans have already been made

Active vs. Passive Humoral Immunity

Active When B cells encounter antigens and produce

antibodies against them Naturally acquired during infections Artificially acquired through vaccines

Most vaccines contain dead or weakened viruses Vaccines keep you from getting most symptoms Vaccines still stimulate antibody production and

memory of antigens Booster shots can intensify immunity later

Active vs. Passive Humoral Immunity

Passive Antibodies are obtained from serum of immune human or

animal B cells NOT challenged Memory does NOT occur Protection is temporary (ends when antibodies degrade in

body) Natural Passive immunity

When mom’s antibodies cross placenta into fetal circulation Artifical Passive immunity

When someone receives immune serum/gamma globulin (Hepatitis, snake bites, botulism, rabies, tetanus)

Monoclonal Antibodies

Produced by descendants of a single cell Are antibodies that are specific for one

antigen Used to deliver cancer-fighting drugs Also used to diagnose Hepatitis, Pregnancy,

Rabies, as well as for early cancer detection

Antibodies

AKA Immunoglobulins (Ig’s) Blood proteins

Proteins secrected by activated B cells or plasma-cell offspring in response to an antigen

Capable of binding with that antigen Formed in response to antgens

Antibodies

Made of 4 Amino Acid chains linked by disulfide bonds

Two heavy chains and two light chains (1/2 the size of heavy chains)

The chains combine to form the antigen-binding site that fits its specific antigen

Antibodies

5 classes (Remember “MADGE”) IgM; IgA; IgD; IgG; IgE

IgD is virtually always attached to B cells IgG is only one that can cross placenta

Also the most abundant IgA is found in mucus and other secretions IgM, IgG can fix complement IgE are “trouble-makers” in allergies

Antibody Function Inactivate antigens

Complement fixation (activation) Triggers events that cause lysis of foreign cells

Neutralization When antibodies bind to sites on foreign cells to cause cell

injury Blocks harmful effects of toxins produced by bacteria/virus

Agglutination Causes clumping of foreign cells (think Blood Transfusion

reactions) Precipitation

When antigen-antibody complexes are so big that they can’t stay dissolved in solution (makes them easily captured)

Cell-Mediated Immune Response

T cells can’t bind with free antigens like B cells

They must recognize an antigen presented by a macrophage AND “self” by binding to the macrophage

The macrophage “feeds” antigens to the T cell (kind of like a double handshake)

Classes of T cell Clones Cytotoxic (Killer) T Cells

Specialize in killing virus-infected, cancer cells, or foreign graft cells (inject toxic poison into CM)

Helper T Cells “Directors/Managers” of Immune System Circulate and recruit other cells to fight

Stimulate B cells to divide Signal for antibody production Release chemicals that rid body of antigens

Stimulate B and T cells to grow/divide Attract more WBC’s to area Enhance macrophage’s ability to destroy microbes (cause

insatiable appetite for them)

Classes of T Cell Clones, cont.

Suppressor T Cells Release chemicals that suppress activity of T and B

cells Help wind down/stop immune response after the antigen

is destroyed Delayed hypersensitivity T Cells

Play a role in allergies and long-term inflammations Memory Cells

Provide memory for each antigen encountered to allow the body to respond quickly next time

Organ Transplants 4 Types of Grafts

Autografts Transplanted from one place to another in same person; IDEAL

Isografts Tissue grafts donated by identical twin; IDEAL

Allografts Taken from unrelated person; Blood Typing/antigen matching must

happen (at least 75% match) Xenografts

Harvested from another species; NEVER SUCCESSFUL Immunosuppressive Therapy

Drugs, radiation (severe side effects) Body can’t protect itself against foreign antigens Most frequent cause of death is by bacterial/viral infection

Allergies

AKA Hypersensitivities Abnormal vigorous immune response to a perceived

“threat” that is harmless Allergen is a type of antigen that causes this response

Immediate (acute) Hypersensitivity Runny nose, watery eyes, itching, hives, restricted air flow

(inhaled allergen) Anaphalactic Shock

When allergen directly enters bloodstream and travels through body

Reaction involves the whole body

Allergies, cont.

Delayed Hypersensitivity Take days to appear (1-3) Allergic contact dermatitis (poison ivy, contact

with heavy metals, cosmetics, deodorant) Skin tests for TB depend on this type of reaction

Immunodeficiencies

SCID (Severe Combined Immunodeficiency Disease) Congenital Not enough B and T cells Minor infections are lethal

AIDS (Acquired Immunodeficiency Syndrome) Interferes with Helper T cell activity

Autoimmune Diseases Occurs when the body produces antibodies and T

cells that attack and damage its own tissues Triggers

Inefficient lymphocyte programming (self-reactive immune cells aren’t eliminated)

“Hidden” antigens or “new self-antigens” caused by mutation or damage to cell

Reaction of antibodies produced against foreign antigens with self-antigens (Strep antibodies can react with heart antigens and cause rheumatic fever)