Chapter 21- Immune System

Memory

The ability to respond faster & more robustly to re-exposure to the same pathogen or foreign agent.

Production of a Clone

The activated T cells divide repeatedly, creating clones of cytotoxic T cells and memory T cells. (A clone is a group of identical cells formed from the same parent cell.) The cytotoxic T cells are killer cells, engaging in cell-to-cell combat. They destroy the pathogen through the use of two mechanisms, punching holes in the pathogen's cell membrane and secreting substances called cytokines, which enhance phagocytic activity. The memory T cells do not participate in the destruction of the pathogen (antigen). These cells "remember" the initial encounter with the antigen. If the antigen is presented at some future time, the memory cells quickly reproduce and thus allow a faster immune response to occur.

Immunoglobulins

The antibodies secreted by the B cells are proteins & constitute the gamma globulin fraction of plasma proteins. There are five major types of immunoglobulins.

T-Cell Activation

The antigen binds to the receptor sites on both the helper T cells and the inactivated cytotoxic T cell. The helper T cell then secretes cytokines, chemicals that activate cytotoxic T cells. Activated cytotoxic T cells bind to pathogens and destroy them.

Antigen Presentation

The antigen, on the surface of the pathogen, is phagocytosed by a macrophage. The macrophage digests the pathogen & pushes the antigen to its surface. The macrophage's ability to push the antigen to its surface is called antigen presentation.

Delayed-Reaction Allergy

The delayed-reaction allergy is so named because it usually takes about 48 hours to occur; its onset is delayed. This type of allergic response can occur in anyone. It usually results from the repeated exposure of the skin to chemicals such as household detergents. Repeated exposure to the chemical activates T cells, which eventually accumulate in the skin.

First Line of Defense

The first line of defense includes mechanical barriers, chemical barriers, & reflexes. Intact skin & mucous membranes serve as mechanical barriers; pathogens cannot cross these structures and enter the body. Destruction of mechanical barriers is an invitation to microbial invasion & subsequent infection. Assisting the skin & mucous membranes with their mechanical defensive functions are their chemical secretions.

Another Name For the Helper T-cell

The helper T-cell is also called the CD4+ T cell (because of a surface protein called CD4). The CD4+ T cell is a marker for immune function, & the progression of HIV infection is monitored by the CD4+ T-cell count. The CD4+ T cell count decreases as the infection progresses.

Immediate-Reaction Allergy

The immediate-reaction allergy, as its name implies, occurs rapidly in response to its stimulus. It is more commonly called immediate hypersensitivity reaction & involves immunoglobulin E, the IgE antibodies

Allergic Reactions

The immune system sometimes forms antibodies to substances not usually recognized as foreign. This response forms the basis of allergic reactions. The two common allergic reactions are the delayed-reaction allergy & the immediate-reaction allergy.

Acquired Immunity

Unlike genetic immunity, acquired immunity is received during a person's lifetime. Acquired immunity comes either naturally or artificially.

Antigen-Antibody Reaction

When antibodies react with antigens directly, the antibodies bind to antigens in a process

Artificially Acquired Immunity

You can also acquire immunity artificially in two ways. The first is by a vaccine; the second is by injection of immune globulin. Both provide artificially acquired immunity.

Agglutination

the antigen-antibody components clump together, or agglutinate. Agglutination makes it easier for the phagocytic cells to destroy the antigen. Under normal conditions, direct attack by the antibodies is not very helpful in protecting the body against invasion by pathogens.

Pyrogens

(From the Latin word for "fire"). The pyrogens stimulate the hypothalamus in the brain to reset the body's temperature, producing a fever. The elevation in temperature is thought to be beneficial in two ways: a fever stimulates phagocytosis & decreases the ability of certain pathogens to multiply.

Drug-Induced Lupus Erythematosus (DIL)

A DIL can develop in response to certain medications; symptoms gradually disappear when the medication is stopped.

Chronic Autoimmune Disease

A chronic autoimmune disease characterized by a hardening of the skin or other organs. The systemic form of the disease may be fatal because of heart, kidney, lung, & intestinal involvement. The limited form of the disease is called CREST.

Active Immunity

A form of acquired immunity in which the body produces its own antibodies against disease-causing antigens.

Passive Immunity

A form of acquired immunity. The short-term immunity that results from the introduction of antibodies from another person or animal. Unlike active immunity, which often lasts a lifetime, passive immunity is short-lived.

Interferons

A group of proteins secreted by cells infected by a virus. The interferons diffuse to surrounding cells where they prevent viral replication, thereby protecting neighboring cells. Interferons also activate NK cells & macrophages, thus boosting the immune system.

Wheal & Flare Reaction

A nongranular white blood cell. There are T lymphocytes (T cells) and B lymphocytes (B cells).

Phagocyte

A phagocyte engulfs, or eats, particles or pathogens, much like an ameba does. The phagocyte's plasma membrane sends out pseudopods ("false feet") that surround the pathogen. The surfaces of the pseudopods then fuse, thereby enclosing the pathogen within the phagocyte. The trapped pathogen encounters a lysosome; the lysosomal membrane fuses with the pathogen, releasing potent enzymes that destroy the pathogen. The process of phagocytosis can be summarized as "ingested (eaten) and digested."

Complement Proteins

A second group of proteins that protect the body. Complement proteins circulate in the blood in their inactive form. When the complement proteins are activated against a bacterium, they swarm over it. The complement attaches to the bacterium's outer membrane and punches holes in it. The holes in the membrane allow fluid and electrolytes to flow into the bacterium, causing it to burst & die. The activated complement proteins perform other functions that enhance phagocytosis & the inflammatory response.

Allergens

Antigens capable of inducing allergy. Allergens that are apt to be involved in this acute type of allergic response include insect venom, drugs such as penicillin, & foods such as peanuts.

Specificity

As stated earlier, with nonspecific immunity, the body need not recognize the specific foreign agent. Specific immunity homes in on a foreign substance, such as the measles virus or ragweed pollen, & provides protection against one specific substance but not others.

Autoimmune System Disorders

Autoimmune system disorders occur when a person's immune system produces antibodies against its own cells; the immune system no longer recognizes self from nonself. There are many autoimmune diseases, including rheumatoid arthritis, Hashimoto thyroiditis, diabetes mellitus (type 1), and rheumatic fever.

Genetic Immunity

Genetic immunity is also called inborn, innate, or species immunity. Your species protects you from many diseases that afflict other species. As a human, you have inherited immunity to certain diseases such as canine heartworm; you are immunologically protected from your pet.

Human Immunodeficiency Virus (HIV).

HIV infection is usually transmitted sexually. Because it is also transmitted through accidental or intended sharing of injection equipment, HIV is a serious threat to hospital workers and others who routinely handle blood or blood-related products or equipment. Initial infection with HIV causes viremia (virus in the blood), which persists for many years and which targets the immune system, particularly the CD4+ T cells (helper T cells).

Contact Dermatitis

Local tissue response to T-cell activity causes skin eruptions and other signs of inflammation. Other forms of contact dermatitis are associated with poison ivy, poison oak, certain cosmetics, & soaps.

Systemic Lupus Erythematosus (SLE)

SLE is a chronic autoimmune disorder. Symptoms are due to inflammation and are highly variable, but all persons experience joint pain (especially fingers, hands, wrist, and knees). A "butterfly" rash over the bridge of the nose and patchy skin color are characteristic of SLE. Persons who experience only the skin symptoms have discoid erythematosus.

Secondary Immunodeficiency Disorders

Secondary immunodeficiency disorders are common, the most common cause being a drug-induced immune deficiency such as the granulocytopenia resulting from cancer chemotherapy. Other causes include radiation therapy, steroid therapy, stress, malignancies, aging, and many diseases, especially infection with the human immunodeficiency virus (HIV).

Specific Immunity: Third Line of Defense

Specific immunity is also called adaptive immunity because the immune cells are able to respond or adapt to newly encountered pathogens or foreign agents. There are two characteristics that distinguish specific immunity from nonspecific immunity: specificity & memory.

T-Cell Activation & Cell-Mediated Immunity

T cells are effective against many pathogens, tumor cells, and foreign tissue such as organ transplants. T cells originate in the red bone marrow and migrate to the thymus gland, where they mature; they then seed other lymphatic tissue, where they eventually encounter an antigen.

Immunoglobulin D (IgD)

An antibody found on the surface of B cells & participates in the activation of B cells.

Immunoglobulin E (IgE)

An antibody that appears in the exocrine secretions such as breast milk, tears, gastrointestinal secretions, & urine.

Humoral Immunity

Because the antibodies are carried by the blood & other tissue fluid (the body "humors").

Inflammation

The responses the body makes when confronted by an irritant. The irritant can be almost anything; common irritants include pathogens, friction, excessive heat or cold, radiation, injuries, & chemicals. Inflammation is characterized by redness, heat, swelling, & pain

Immunodeficiency Disorder

Disorders caused by an impaired immune response. Immunodeficiency disorders are classified as primary or secondary.

Rheumatic Fever

An immune disorder in which the antibodies produced in response to a streptococcal infection attack the heart muscle & its valves.

Antibodies

Antibodies destroy antigens. They accomplish this task directly by attacking the antigen & indirectly by activating complement proteins that in turn facilitate the attack on the antigens.

Immunotolerance

Recognition of self.

Antigen

A substance that stimulates the formation of antibodies. In fact, the word antigen is made up of words that refer to antibody generating. Antigens are generally large molecules; most are proteins, but a few are polysaccharides and lipids. Antigens are found on the surface of many substances, such as pathogens, red blood cells, pollens, foods, toxins, & cancer cells. Foreign substances that display antigens are described as antigenic. Antigenic substances are attacked by macrophages and lymphocytes.

Fever

Also known as pyrexia is an abnormal elevation in body temperature.

CREST

An acronym for the five main signs. - Calcinosis - Raynaud's syndrome - Esophageal dysfunction - Sclerodactyly (hardness of fingers or toes) - Telangiectasia. CREST usually spares the lungs & kidneys.

Immunoglobulin M (IgM)

An antibody found in blood plasma. The anti-A & anti-B antibodies associated with red blood cells are a type of IgM antibody.

Immunoglobulin G (IgG)

An antibody found in plasma & tissue fluids. It is particularly effective against certain bacteria, viruses, & toxins.

Immunoglobulin A (IgA)

An antibody found primarily in the secretions of exocrine glands. IgA in milk, tears, and gastric juice helps protect against infection. Breast milk contains IgA antibodies & helps the infant ward off infection.

Vaccine

An antigen-bearing substance, such as a pathogen, injected into a person in an attempt to stimulate antibody production.

Antibody-Mediated Immunity (AMI)

An immune response where B cells interact with the antigen indirectly, through the secretion of antibodies.

Cell-Mediated Immunity (CMI)

An immune response where T cells attack antigens directly, through cell-to-cell contact.

B-Cell Activation and Antibody-Mediated Immunity

B cells engage in AMI. Activated B cells produce antibody-secreting plasma cells. The antibodies are carried by the blood and body fluids to the antigen-bearing pathogens (antigens) that usually reside in the plasma or other extracellular fluid. B cells can produce over 10 million different antibodies; each B cell interacts with a specific antigen and produces its own antibody. The large numbers of antibodies allow the body to develop immunity against many different diseases.

Infection

Inflammation caused by a pathogenic organism.

Macrophanges

Macrophages function as phagocytes—"big eaters," as their name implies. The macrophages play another important defensive role. They assist the lymphocytes as antigen-presenting cells in mounting an immune response.

Natural Killer Cells (NK Cells)

NK cells are a small population of a special type of lymphocyte that acts nonspecifically to kill a variety of cells. NK cells are effective against many microbes and certain cancer cells. NK cells cooperate with the specific defense mechanisms to mount the most effective defense possible.

Nonspecific Immunity

Nonspecific immunity is also called innate immunity because we are born with certain defensive mechanisms that do not require prior exposure to the pathogen or foreign agent. A number of defense mechanisms are included in the category of nonspecific immunity. Nonspecific immunity can be divided into two lines of defense. The first line of defense includes mechanical barriers, chemical barriers, and reflexes. The second line of defense includes phagocytosis, inflammation, fever, protective proteins (interferons and complement proteins), & natural killer (NK) cells. Remember that the nonspecific defense mechanisms work against all foreign agents or type of injury; no recognition of a specific agent or injury is necessary.

Other Immune Responses

Normally the immune system protects the body from non-self; foreign agents are recognized and eliminated. Sometimes, however, the immune system goes awry: it attacks the self, causing autoimmune disease, or it overreacts, causing allergies.

Monocytes

Phagocytes consist of the agranulocytic monocytes. Some monocytes circulate within the blood; they are described as free and motile. Other monocytes leave the blood, develop into macrophages, & become fixed in lymphatic tissue throughout the body.

Primary Immunodeficiency Disorders

Primary immunodeficiency disorders are rare, an example being severe combined immunodeficiency disease (SCID).

Acquired Immunodeficiency Syndrome (AIDS)

The late & severe manifestation of HIV infection is called acquired immunodeficiency syndrome (AIDS). At this stage all organ systems are adversely affected, and death is most often caused by infection.

Phagocytosis

The leukocytes ingest & digest pathogens & other foreign substances. Two important phagocytes are the neutrophils & monocytes.

Neutorphils

The neutrophils are small & motile, & they travel to the site of infection quickly. There they engage the pathogen aggressively, & most die in battle, becoming part of the cellular debris & pus. The neutrophils are also active in the absence of infection; they constantly wander throughout the connective tissue, killing bacteria before they have a chance to grow and multiply. Adding to its phagocytic bag of tricks, the neutrophil, when prompted to phagocytose, secretes & surrounds itself in a cloud of bactericidal chemicals. The neutrophil thus feasts away in a phagocytic-friendly chemical killing zone.

Second Line of Defense

The second line of defense includes phagocytosis, inflammation, fever, protective proteins, & NK cells.

Anaphylaxis (Anaphylactic Shock)

The systemic effects can be severe; they include massive vasodilation, which causes a sharp drop in blood pressure & a severe constriction of the respiratory passages (bronchoconstriction), making breathing extremely difficult and, in some cases, impossible. This severe form of the immediate hypersensitivity reaction is called anaphylaxis. Persons allergic to penicillin are at particular risk for anaphylaxis. As a result, always ask a person about allergies to medications before administering any type of drug, particularly antibiotics. (Some persons are even allergic to aspirin.) The immediate administration of a drug such as epinephrine (adrenalin) is particularly effective because it "opens up" breathing passages and elevates blood pressure. Most persons who are prone to anaphylactic responses carry a source of injectable epinephrine.

Types of Immunity

The two main categories of immunity are genetic immunity & acquired immunity.

Lymphocytes

The two types of lymphocytes are T lymphocytes (T cells) & B lymphocytes (B cells). Although both come from the stem cells in the bone marrow, they differ in their development & functions.

Immunization

The use of a dead or attenuated pathogen to stimulate antibody production. The solution of dead or attenuated pathogens is the vaccine. Because the use of a vaccine stimulates the body to produce its own antibodies, vaccines induce active immunity.

Immune

To be exempt or protected from a particular disease.

Steps of Immediate Hypersensitivity Reaction

• Step 1. An allergen (red dot) activates a B cell. • Step 2. The activated B cell forms a clone of antibody-secreting plasma cells & memory B cells. • Step 3. The plasma cells secrete large amounts of IgE antibodies against the specific allergen. • Step 4. The IgE antibodies bind to the mast cells in body tissues. • Step 5. More of the allergen invades the body. The allergen binds with the IgE antibodies on the mast cells. The mast cells release large amounts of histamine, leukotrienes, & other chemicals that cause systemic effects, especially issues regarding blood pressure & impaired breathing.

Antibody-Mediated Immunity

• Step 1. The B cell originates and matures in the red bone marrow; it then seeds other lymphatic tissue where it eventually encounters an antigen. • Step 2—antigen presentation. A macrophage engulfs and processes an antigen. The antigen is pushed to the surface of the macrophage. • Step 3—B-cell and helper T-cell activation. The presented antigens bind to the B cell and helper T cell. Cytokines from the activated helper T cells participate in B-cell activation. • Step 4—production of a clone. The B cells reproduce, creating clones of plasma cells and memory B cells. Plasma cells secrete large quantities of antibodies that travel through the blood to the foreign antigens (pathogens). The memory B cells do not participate in the attack; they remember the specific antigen during future encounters and allow a quicker response to the invading pathogen (antigen).