13-Body Defense Mechanisms

effects of complement system

Destruction of pathogen. Complement can act directly by punching holes in a target cell's membrane so that the cell is no longer able to maintain a constant internal environment. Just as when NK cells secrete proteins that make a target cell's membrane leaky, water enters the cell, causing it to burst. Enhancement of phagocytosis. Complement enhances phagocytosis in two ways. First, complement proteins attract macrophages and neutrophils to the site of infection to remove the foreign cells. Second, one of the complement proteins binds to the surface of the microbe, making it easier for macrophages and neutrophils to "get a grip" on the intruder and devour it. Stimulation of inflammation. Complement also causes blood vessels to widen and become more permeable. These changes provide increased blood flow to the area and increased access for white blood cells.

four cardinal signs of inflammation that occur at the site of a wound are

redness, heat, warmth swelling, pain

Suppressor T cells

releases chemicals that dampen the activity of both B cells and T cells. Suppressor T cells turn off the adaptive immune response when the antigen no longer poses a threat. This may be a mechanism that prevents the immune system from overreacting and harming healthy body cells.

natural killer cells (NK cells)

roams the body in search of abnormal cells and quickly orchestrates their death. In a sense, NK cells function as the body's police walking a beat. They are not seeking a specific villain. Instead, they respond to any suspicious character, including a cell whose cell membrane has been altered by the addition of proteins that are unfamiliar to the NK cell. The prime targets of NK cells are cancerous cells and cells infected with viruses. -As soon as it touches a cell with an abnormal surface, the NK cell attaches to the abnormal cell and delivers a "kiss of death" in the form of proteins that create many pores in the target cell. The pores make the target cell "leaky," so that it can no longer maintain a constant internal environment and eventually bursts.

monoclonal antibodies

Groups of identical antibodies that bind to one specific antigen

HIV attacks many types of white blood cells. Disabling which blood cell type prevents the activation of the entire immune response?

Helper T Cells

When a macrophage first encounters a pathogen, it activates _____ T cells, which then activate _____ T cells.

Helper; Cytotoxic

The class of antibody found in breast milk, saliva, and tears is _____.

IgA

Classes of Antibodies

IgG, IgM, IgA, IgD, IgE

MHC markers

self labels on your cells are different from those of any other person (except an identical twin) as well as from those of other organisms, including pathogens. The immune system uses these labels to distinguish what is part of your body from what is not -It doesn't attack cells that are recognized as self.

three strategies for defending against foreign organisms and molecules or cancer cells.

Keep the foreign organisms or molecules out of the body in the first place. This is accomplished by the first line of defense—chemical and physical surface barriers. Attack any foreign organism or molecule or cancer cell inside the body. The second line of defense consists of internal cellular and chemical defenses that become active if the surface barriers are penetrated. Destroy a specific type of foreign organism or molecule or cancer cell inside the body. The third line of defense is the adaptive immune response, which destroys specific targets (usually disease-causing organisms) and remembers those targets so that a quick response can be mounted if they enter the body again.

B lymphocytes (B cells)

Lymphocyte that matures in the bone marrow and secretes antibodies.

T lymphocytes (T cells)

Lymphocyte that matures in the thymus and acts directly against antigens in cell-mediated immune responses.

Which of the following mechanisms are used by antibodies to defend the body against pathogens?

Lysis Neutralization Precipitation

Which of the following functions as an antigen-presenting cell (APC)?

Macrophage

Cancerous cells routinely form within our body. What type of cell destroys them?

Natural Killer Cells

Antibodies help defend against these pathogens in several ways that can be remembered with the acronym PLAN:

Precipitation. The antigen-antibody binding causes antigens to clump together and precipitate (settle out of solution), enhancing phagocytosis by making the antigens easier for phagocytic cells to capture and engulf. Lysis (bursting). Certain antibodies activate the complement system, which then pokes holes through the membrane of the target cell and causes it to burst. Attraction of phagocytes. Antibodies also attract phagocytic cells to the area. Phagocytes then engulf and destroy the foreign material. Neutralization. Antibodies bind to toxins and viruses, neutralizing them and preventing them from causing harm.

Physical barriers to infection

skin and mucous membranes

Examples of barrier defenses include _____.

skin, mucous membranes, and saliva

Chemicals that cause the hypothalamus to raise the body’s set point for temperature and initiate fever are called _____.

Pyrogens

2) Detection

Recall that macrophages are phagocytic cells that roam the body, engulfing any foreign material or organisms they may encounter. Within the macrophage, the engulfed material is digested into smaller pieces.

What molecules are found on the surface of both T lymphocytes and B lymphocytes that identify foreign invaders?

Receptors

Pain

Several factors cause pain in an inflamed area. For example, the excessive fluid leaking into the tissue presses on nerves and contributes to the sensation of pain. -Some soreness might be caused by bacterial toxins, which can kill body cells. -Injured cells also release pain-causing chemicals, such as prostaglandins. -Pain usually prompts a person to protect the area to avoid additional injury.

What is our primary physical barrier against disease?

Skin

chemical barriers to infection

sweat and oil glands in the skin lining of the stomach urine saliva tears

1) Threat

The adaptive immune response begins when a molecule or organism (an antigen) lacking the self (MHC)

active immunity

the body actively defends itself by producing memory B cells and T cells following exposure to an antigen. -Active immunity happens naturally whenever a person gets an infection. -Fortunately, active immunity can also develop through vaccination (also known as immunization), a procedure that introduces a harmless form of an antigen into the body to stimulate adaptive immune responses against that antigen.

6b) Defense—The Cell-Mediated Response

The cytotoxic T cells are the effector T cells responsible for the cell-mediated immune response that destroys antigen-bearing cells. -Each cytotoxic T cell is programmed to recognize a particular antigen bound to MHC markers on the surface of a cellular pathogen, an infected or cancerous body cell, or on cells of a tissue or organ transplant. -A cytotoxic T cell becomes activated to destroy a target cell when two events occur simultaneously -First, the cytotoxic T cell must encounter an antigen-presenting cell, such as a macrophage. -Second, a helper T cell must release a chemical to activate the cytotoxic T cell. -When activated, the cytotoxic T cell divides, producing memory cells and effector cytotoxic T cells. -An effector cytotoxic T cell releases chemicals called perforins, which cause holes to form in the target cell membrane. -The holes are large enough to allow some of the cell's contents to leave the cell so that the cell disintegrates. -The cytotoxic T cell then detaches from the target cell and seeks another cell having the same type of antigen.

Heat

The increased blood flow also elevates the temperature in the area of injury. The elevated temperature raises the metabolic rate of the body cells in the region and speeds healing. Heat also increases the activities of phagocytic cells and other defensive cells.

Swelling

The injured area swells because histamine also makes capillaries more permeable, or leakier, than usual. -Fluid seeps into the tissues from the bloodstream, bringing with it many beneficial substances. -Blood- clotting factors enter the injured area and begin to wall off the region, thereby helping to protect surrounding areas from injury and preventing excessive loss of blood. -The seepage also increases the oxygen and nutrient supply to the cells. -If the injured area is a joint, swelling can hamper movement—an effect that might seem to be an inconvenience, but that actually permits the injured joint to rest and recover.

3) Alert

The macrophage then alerts the immune system's commander, a helper T cell, that an antigen is present. -The macrophage accomplishes this task by transporting some of the digested pieces to its own surface, where they bind to the MHC self markers on the macrophage membrane. -On the one hand, the self marker acts as a secret password that identifies the macrophage as a "friend." -On the other hand, the antigen bound to the self marker functions as a kind of wanted poster, telling the lymphocytes that there is an invader and revealing how the invader can be identified. -The displayed antigens trigger the adaptive immune response. Thus, the macrophage is an important type of antigen-presenting cell (APC). (B cells and dendritic cells—cells with long extensions found in lymph nodes—are two other kinds of antigen-presenting cells.) -the macrophage presents the antigen to a helper T cell, the kind of T cell that serves as the main switch for the entire adaptive immune response. -However, the macrophage must alert the right kind of helper T cell—a helper T cell bearing receptors that recognize the specific antigen being presented. -These specific helper T cells constitute only a tiny fraction of the entire T cell population. -Finding the right helper T cell is like looking for a needle in a haystack. -The macrophage wanders through the body until it literally bumps into an appropriate helper T cell. The encounter most likely occurs in one of the lymph nodes, because these bean-shaped structures, contain huge numbers of lymphocytes of all kinds. -When the antigen-presenting macrophage meets the appropriate helper T cell and binds to it, the macrophage secretes a chemical that activates the helper T cell.

5) Building Specific Defenses

When the appropriate "naive"1 B cells or T cells are activated, they begin to divide repeatedly. -The result is a clone (a population of genetically identical cells) that is specialized to protect against the particular target antigen.

4) Alarm

Within hours, an activated helper T cell begins to secrete its own chemical messages. The helper T cell's message calls into active duty the appropriate B cells and T cells—those with receptors that recognize the particular antigen that triggered the response, which is the antigen displayed by the antigen-presenting cell.

complement system

a group of at least 20 proteins whose activities enhance, or complement, the body's other defense mechanisms. Until these proteins are activated by infection, they circulate in the blood in an inactive state. Once activated, these proteins enhance both nonspecific and specific defense mechanisms.

When macrophages properly alert helper T cells

they respond by calling out the body's specific defensive forces, and the adaptive immune responses begin.

Adaptive immunity includes the _____.

third line of defense

6a) Defense—The Antibody-Mediated Response

activated B cells divide. -The effector cells they produce through clonal selection, which are called plasma cells, secrete antibodies into the bloodstream to defend against antigens free in the blood or bound to a cell surface -Antibodies are Y-shaped proteins that recognize a specific antigen by its shape. -Each antibody is specific for one particular antigen. The specificity results from the shape of the proteins that form the tips of the Y. -Because of their shapes, the antibody and antigen fit together like a lock and a key. Each antibody can bind to two identical antigens, one at the tip of each arm on the Y

clonal selection

antigens bind to specific receptors, causing a fraction of lymphocytes to clone themselves

Antibodies can bind only to

antigens that are free in body fluids or attached to the surface of a cell. Their main targets are toxins and extracellular microbes, including bacteria, fungi, and protozoans.

While _____ cause normal immune responses, _____ cause asthma.

antigens; allergens

Cytotocix T cells

are the effector T cells responsible for the cell-mediated immune response

Neutrophils

arrives at the site of attack before the other types of white blood cells and immediately begins to consume the pathogens, especially bacteria, by phagocytosis

Injection of anti-hepatitis antibodies after exposure to hepatitis A is an example of _____ immunity.

artificial passive

Eosinophils

attacks pathogens that are too large to be consumed by phagocytosis, such as parasitic worms. Eosinophils get close to the parasite and discharge enzymes that destroy the organism. Macrophages then remove the debris.

effector cells

carry out the attack on the enemy. -Effector cells generally live for only a few days. -Thus, after the invader has been eliminated from the body, the number of effector cells declines.

Fever

caused by pyrogens

Which of the following cells attack abnormal or foreign cells using perforins?

cytotoxic T Cells

Antibody-mediated immune response

defend primarily against antigens found traveling freely in intercellular and other body fluids —for example, toxins or extracellular pathogens such as bacteria or free viruses. The warriors of this branch of immune defense are the effector B cells (also called plasma cells), and their weapons are Y-shaped proteins called antibodies, which neutralize and remove potential threats from the body. -Antibodies are programmed to recognize and bind to the antigen posing the threat

inflammatory response

destroys invaders and helps repair and restore damaged tissue

Pathogens

disease causing agents

Phagocytes

engulf pathogens, damaged tissue, or dead cells by the process of phagocytosis -scavenger cells -This class of white blood cells serves not only as the front-line soldiers in the body's internal defense system but also as janitors that clean up debris.

Macrophages

have hearty and less discriminating appetites than neutrophils do, and they attack and consume virtually anything that is not recognized as belonging in the body—including viruses, bacteria, and damaged tissue

The four signs of the inflammatory reaction are caused by _____.

histamine and vasodialation

antibodies are also called

immunoglobulins

Interferons

inhibit cell division of cancer cells -First, they help rid the body of virus-infected cells by attracting macrophages and NK cells that destroy the infected cells immediately. -Second, interferons warn cells that are not yet infected with the virus to take protective action. When released, interferons diffuse to neighboring cells and stimulate them to produce proteins that prevent viruses from replicating in those cells. Because viruses cause disease by replicating inside body cells, preventing replication curbs the disease. Interferons help protect uninfected cells from all strains of viruses, not just the one responsible for the initial infection.

Allergy

is an overreaction by the immune system to an antigen, in this case called an allergen. -The immune response in an allergy is considered an overreaction because the allergen itself usually is not harmful to the body. -The most common allergy is hay fever

passive immunity

is protection that results when a person receives antibodies produced by another person or animal. -For instance, some antibodies produced by a pregnant woman can cross the placenta and give the growing fetus some immunity. -These maternal antibodies remain in the infant's body for as long 3 months after birth, at which point the infant is old enough to produce his or her own antibodies. -Antibodies in breast milk also provide passive immunity to nursing infants, especially against pathogens that might enter through the intestinal lining -The mother's antibodies are a temporary yet critical blanket of protection, because most of the pathogens that would otherwise threaten the health of a newborn have already been encountered by the mother's immune system.

What is the advantage of immunological memory?

it saves time

Monocytes

leave the vessels of the circulatory system and enter the tissue fluids, where they develop into large macrophages

memory cells

long-lived cells that "remember" that particular invader and mount a rapid, intense response to it if it should ever appear again. The quick response of memory cells is the mechanism that prevents you from getting ill from the same pathogen twice.

What causes the production of interferons?

viruses

7) Continued Surveillance

-The first time an antigen enters the body, only a few lymphocytes can recognize it. -Those lymphocytes must be located and stimulated to divide in order to produce an army of lymphocytes ready to eliminate that particular antigen. -As a result, the primary response, the one that occurs during the body's first encounter with a particular antigen, is relatively slow. -A lapse of several days occurs before the antibody concentration begins to rise, and the concentration does not peak until 1 to 2 weeks after the initial exposure to the antigen

adaptive immune response

-When first and second responses fail -provides the specific responses and memory needed to target the invader. -The organs of the lymphatic system are important components of the immune system because they produce the various cells responsible for immunity

Steps of adaptive immune response

1) Threat 2)Detection 3)Alert 4)Alarm 5) Building Specific Defenses 6a) Defense—The Antibody-Mediated Response 6b) Defense—The Cell-Mediated Response 7) Continued Surveillance

If the immune system mistakenly launches an attack against “self†cells, it is the _____ cells that cause lifelong autoimmune problems.

memory cells

types of phagocytes

neutrophils, monocytes, macrophages

antigens

nonself substance -not recognized as belonging in the body, the immune system directs an attack against it. Typically, antigens are large molecules, such as proteins, polysaccharides, or nucleic acids. Often, antigens are found on the surface of an invader—embedded in the plasma membrane of an unwelcome bacterial cell, for instance, or part of the protein coat of a virus. However, pieces of invaders and chemicals secreted by invaders, such as bacterial toxins, can also serve as antigens. Each antigen is recognized by its shape.

autoimmune disorder

occur when the immune system fails to distinguish between self and nonself and attacks the tissues or organs of the body. If the immune system can be called the body's military defense, then autoimmune disease is the equivalent of friendly fire.

Redness

occurs because blood vessels dilate (widen) in the damaged area, causing blood flow in this area to increase. -The dilation is caused by histamine, a substance also released during allergic reactions (discussed later in the chapter). -Histamine is released by small, mobile connective tissue cells called mast cells in response to chemicals from damaged cells.

Which cell type produces antibodies?

plasma cells

A substance that triggers an immune response is called a(n) _____, while a disease-causing agent is called a(n) _____.

Antigen; Pathogen

cell-mediated immune response

protect against cellular pathogens or abnormal cells, including body cells that have become infected with viruses or other pathogens and cancer cells. -The lymphocytes responsible for cell-mediated immune responses are a type of T cell called cytotoxic T cell (discussed at greater length later in the chapter). -Once activated, cytotoxic T cells quickly destroy the cellular pathogen, infected body cells, or cancerous cells by causing them to burst.