Unit 4 - Chapter 37

Vaccinations produce immunity against disease

-A vaccine stimulates an immune response by exposing a person to antigens produced by a pathogen -Vaccines often consist of weakened or killed microbes, or some of the pathogen's antigens, usually synthesized using genetic engineering techniques -Exposure to these antigens results in the body producing an army of memory cells that confer immunity against living microbes of the same type

Humoral immunity fights invaders that are outside cells

-Antibodies are large proteins that cannot readily cross plasma membranes, so they usually do not enter cells -A humoral response is, therefore, effective against microbes or their toxins only when they are outside the cells, generally in the blood, lymph, or interstitial fluid

Humoral immunity is produced by antibodies dissolved in the blood

-Humoral immunity is provided by B cells and the antibodies that they secrete into the bloodstream -When a microbe enters the body, the antibodies of only a few of these B cells can bind to antigens on the invader -Antigen-antibody binding causes these B cells to multiply rapidly -This process is called clonal selection because the antigens "select" which B cells will multiply

Antigens

-Large, complex molecules that can trigger an adaptive immune responses are called antigens, which is short for antibody generating molecules

The adaptive immune system recognizes invaders' complex molecules

-Large, complex molecules that can trigger an adaptive immune responses are called antigens, which is short for antibody generating molecules -Antigens are often located on the surfaces of invading microbes -Many viral antigens become incorporated into the plasma membranes of infected body cells -Viral or bacterial antigens are also "displayed" on the plasma membranes of dendritic cells and macrophages that engulf them -Other antigens, such as toxins released by bacteria, may be toxins in the blood plasma, lymph, or interstitial fluid -Antigens are not confined to invading microbes and their toxins -Any large, complex molecule, including molecules of the cells of your own body, may be an antigen and provoke an immune response

T-cell receptors

-T-cell receptors are found on the surfaces of T cells -Every T cell produces T-cell receptors that differ from those of all other T cells -Variable regions, which form highly specific binding sites for antigens, protrude from the cell surface

The adaptive immune system simultaneously launches two types of attack against microbial invaders

1. Humoral immunity 2. Cell-mediated immunity

vaccine

A vaccine stimulates an immune response by exposing a person to antigens produced by a pathogen

Inflammatory response

A wound provokes the inflammatory response, which recruits phagocytes to the site of injury

Cell-mediated immunity

Cell-mediated immunity is produced by cytotoxic T cells, which attack virus-infected body cells and cells that have become cancerous

Helper T cells

Helper T cells bear T-cell receptors that bind to antigens displayed on the surfaces of dendritic cells or macrophages that have engulfed and digested invading microbes

Phagocytes

One brigade, collectively called phagocytes, ingests foreign invaders and cellular debris by phagocytosis

Regulatory T cells

One of the functions of regulatory T cells is to prevent any remaining self-reactive lymphocytes from attacking the body's own cells

Pathogens

produce disease

Humoral antibodies have multiple modes of action against invaders

-Antibodies in the blood combat invading molecules or microbes in three ways 1. The circulating antibodies may bind to a foreign molecule, virus, or cell and render it harmless by a process called neutralization -An example of neutralization is an antibody covering the active site of a toxic enzyme in snake venom 2. Antibodies may coat the surface of invading molecules, viruses, or cells and make it easier for macrophages and phagocytes to destroy them 3. When antibodies bind to antigens on the surface of a microbe, the antibodies interact with complement proteins that are always present in the blood

Clonal selection

-Antigen-antibody binding causes these B cells to multiply rapidly -This process is called clonal selection because the antigens "select" which B cells will multiply

How Does Medical Care Assist the Immune Response?

-The battle against disease, for most of human history, was fought by the immune response alone -Currently, the immune response has a powerful assistant: medical treatment -Antimicrobial drugs and vaccinations are two very important medical tools

lymph nodes

-The human body contains about 500 lymph nodes scattered along the lymph vessels -Lymph nodes contain masses of macrophages and lymphocytes lining narrow passages through which lymph flows

All adaptive immune responses include the same three steps

1. Lymphocytes recognize an invading microbe and distinguish the invader from self 2. They launch an attack 3. They retain a memory of the invader that allows them to ward off future infections by the same type of microbe

The daughter cells differentiate into two cell types

1. Memory B cells, which do not release antibodies, but play an important role in future immunity to the invader that stimulated their production 2. Plasma cells, which become enlarged and packed with rough endoplasmic reticulum, which synthesizes huge quantities of antibodies -These antibodies are released into the bloodstream

Severe combined immune deficiency (SCID),

About 1 in 60,000 children is born with severe combined immune deficiency (SCID), which occurs when any of several genetic defects cause few or no immune cells to be formed

Antibodies

Antibodies, proteins produced by B cells and their offspring, help the immune system to recognize invading microbes and destroy them

Cytokines

There are dozens of different cytokines that are used for communication between cells

The adaptive immune system can recognize millions of different antigens

- The adaptive immune system recognizes and responds to millions of potentially harmful antigens -B and T cells randomly synthesize millions of different antibodies and T-cell receptors -At any given time, the human body contains perhaps 100 million different antibodies and even more T-cell receptors

The inflammatory response attracts phagocytes to injured or infected tissue

-A wound provokes the inflammatory response, which recruits phagocytes to the site of injury -The inflammatory response causes tissues to become warm, red, swollen, and painful -The inflammatory response begins when damaged cells release chemicals that cause certain cells in the connective tissue, called mast cells, to release histamine -Histamine relaxes the smooth muscle surrounding arterioles, increasing blood flow and causing capillary walls to become leaky -Extra blood flowing through leaky capillaries drives fluid from the blood and into the wounded area, causing redness, warmth, and swelling -Histamine relaxes the smooth muscle surrounding arterioles, increasing blood flow and causing capillary walls to become leaky -Extra blood flowing through leaky capillaries drives fluid from the blood and into the wounded area, causing redness, warmth, and swelling -Other chemicals released by the wounded cells, mast cells, and some substances produced by the microbes themselves attract macrophages, neutrophils, and dendritic cells -These cells squeeze out through the leaky capillary walls and ingest bacteria, dirt, and cellular debris -In some cases, pus may accumulate -Other chemicals released by injured cells initiate blood clotting to reduce blood loss and prevent more microbes from entering the bloodstream -Swelling and some of the chemicals released by the injured tissue cause pain, which usually leads to protective behaviors that reduce the likelihood of further injury

How Does the Adaptive Immune System Remember Its Past Victories?

-After recovering from a disease, you remain immune to that particular microbe for many years, perhaps a lifetime -Some of the daughter cells of the original B cells, cytotoxic T cells, and helper T cells that responded to the original infection differentiate into memory B cells and memory T cells that survive for many years -If the body is reinvaded by the same type of microbe, the memory cells recognize the invader and mount an immune response -Memory B cells rapidly produce a clone of plasma cells, secreting antibodies that combat this second invasion -Memory T cells produce clones of either helper T cells or cytotoxic T cells specific for the "remembered" invader -Memory cells respond so quickly and so largely in a second infection, the body fends off the attack before the person suffers any symptoms—the person has become immune -Acquired immunity confers long-lasting protection against many diseases such as smallpox, measles, mumps, and chicken pox

Allergies are misdirected immune responses

-Allergies are immune reactions to harmless substances -Common allergies include those to pollen, mold spores, bee or wasp venoms, and foods such as milk, eggs, fish, wheat, tree nuts, and peanuts -An allergic reaction begins when allergy-causing antigens, called allergens, enter the body and bind to "allergy antibodies" on a special type of B cell -This B cell proliferates, producing plasma cells that pour out allergy antibodies into the plasma -The antibodies attach to mast cells, mostly in the respiratory and digestive tracts -If allergens later bind to these attached antibodies, they trigger the release of histamine, which causes leaky capillaries and other symptoms of inflammation -In the respiratory tract, histamine increases mucous secretions and results in symptoms such as a runny nose, sneezing, and congestion typical of "hay fever" -Food allergies may cause intestinal cramps and diarrhea -Some reactions are so strong that the airways may completely close, causing death by suffocation

What Happens When the Immune System Malfunctions?

-An autoimmune disease is an immune response against the body's own molecules -Occasionally, our immune system produces "anti-self" antibodies -The result is an autoimmune disease in which the immune system attacks a component of one's own body -Some types of anemia are caused by antibodies that destroy a person's red blood cells -Type 1 diabetes begins when the immune system attacks the insulin-secreting cells of the pancreas -Other autoimmune diseases include rheumatoid arthritis (which affects the joints), myasthenia gravis (skeletal muscle), multiple sclerosis (central nervous system), and systemic lupus (almost any part of the body) -There are no known cures for autoimmune diseases -Replacement therapy can alleviate the symptoms—for instance, by giving insulin to diabetics The autoimmune response can be reduced with drugs that suppress the immune response -This course of action also reduces responses to the everyday assaults of disease microbes, so the therapy has major drawbacks

Antimicrobial drugs kill microbes or slow down microbial reproduction

-Antibiotics are chemicals that help combat infection by killing or interfering with the multiplication of bacteria, fungi, or protists -The occasional mutant microbe that is resistant to an antibiotic will pass on the genes for resistance to its offspring; resistant microbes thrive while susceptible microbes die off -Eventually, many antibiotics become ineffective in treating diseases -Antibiotics are not effective against viruses because they target metabolic processes that viruses do not possess -Antiviral drugs are now available that target different stages of the viral cycle of infection, including attachment to a host cell, replication of viral parts, assembly of new viruses within the host cell, and the release of these viruses to infect more body cells -Antiviral drugs are available to treat HIV, herpes virus (cold and genital sores), and the flu virus

Helper T cells enhance both humoral and cell-mediated immune responses

-B cells and cytotoxic T cells require assistance from helper T cells -Helper T cells bear T-cell receptors that bind to antigens displayed on the surfaces of dendritic cells or macrophages that have engulfed and digested invading microbes -When its receptor binds an antigen, a helper T cell multiplies rapidly, and its daughter cells differentiate and release cytokinins that stimulate cell division and differentiation in both B cells and cytotoxic T cells

The immune system recognizes most cancerous cells as foreign

-Cancer cells form in our bodies every day, but are destroyed by the immune system -The surfaces of most cancer cells either lack some of the usual proteins found on normal body cells or bear proteins that are unique to cancers, especially cancers caused by viruses -Natural killer cells and cytotoxic T cells recognize these protein differences as markers of non-self cells and destroy the cancer cells -Some cancer cells evade detection because they do not bear antigens that allow the immune system to recognize them as foreign

Cancer

-Cancer, the uncontrolled replication of the body's own cells, is one of the most dreaded diseases in the world -More than 600,000 people in the United States will die of cancer this year, a fatality rate second only to heart disease -Cancers may be triggered by many causes, including environmental factors, faulty genes, mistakes during cell division, and viruses -These triggers sabotage the mechanisms that normally control the growth of the body's cells, causing cancer

Complement

-Complement proteins are mostly synthesized by the liver and circulate in the blood plasma -They assist the immune system in killing invading microbes

-Fever combats large-scale infections

-If invaders breach these defenses and mount a full-blown infection, they may trigger a fever, which slows down microbial reproduction and enhances the body's own fighting abilities -The onset of fever is controlled by the hypothalamus, the part of the brain housing temperature-sensing nerve cells that serve as the body's thermostat -In humans, the thermostat is set at about 97º to 99ºF -Certain types of bacteria, as well as the phagocytic cells that respond to an infection, produce chemicals called pyrogens -Pyrogens travel in the bloodstream to the hypothalamus and raise the thermostat's set point -The body responds with increased fat metabolism, constriction of blood vessels supplying the skin, and behaviors such as shivering and bundling under blankets -Pyrogens also cause other cells to reproduce the concentration of iron in the blood -An elevated body temperature increases the activity of phagocytic white blood cells while simultaneously slowing bacterial reproduction -Fever causes the cells of the adaptive immune system to multiply more rapidly, hastening the onset of an effective adaptive immune response -Fever also stimulates cells infected by viruses to produce a protein called interferon, which travels to other cells and increases their resistance to viral attack -Interferon also stimulates natural killer cells that destroy virus-infected body cells -On the other hand, high fevers are uncomfortable and may be dangerous -Extremely high fevers can cause brain damage, but this is rare

What Are the Key Components of the Adaptive Immune System?

-If the nonspecific defenses are breached, the body mounts a highly specific and coordinated adaptive immune response directed against the particular organism that has successfully colonized the body -He observed that sometimes a person would contract a disease, recover, and never catch that disease again

Invertebrate animals possess nonspecific lines of defense

-Invertebrates are protected only by nonspecific external barriers and nonspecific internal defenses -Different invertebrates possess an enormous range of external barriers, ranging from exoskeletons to slimy secretions -Internally, invertebrates have white blood cells that attack pathogens and secrete proteins that neutralize invaders or the toxins they release

-Antibodies and T-cell receptors trigger immune responses to antigens

-Lymphocytes produce two types of proteins that bind to specific antigen and trigger an immune response -Antibodies and T-cell receptors -Antibodies are manufactured only by B cells and their offspring -Antibodies are Y-shaped proteins composed of two pairs of peptide chains: one pair of identical large (heavy) chains and one pair of identical small (light) chains -Both heavy and light chains consist of a variable region, which differs among individual antibodies, and a constant region, which is the same in all antibodies of the same type -The light and heavy chains combine to form the two functional parts: the "arms" of the Y and the "stem" of the Y -The variable regions at the arm tips form sites that bind antigens -Each binding site has a particular size, shape, and electrical charge so that only certain molecules can fit in and bind to the antibody -The sites are so specific that each antibody can bind only a few, very similar types of antigen molecules -The stem of the Y is composed of the constant region of the heavy chains -The stem determines where the antibody is located and what role it plays in the immune response -There are five major types of antibodies -IgM, IgD, IgG, IgA, and IgE -The antibodies differ in location and function -IgM and IgD antibodies are attached to the surfaces of B cells -When an IgM or IgD antibody on the surface of a B cell binds an antigen, this triggers multiplication of the B cell -IgG antibodies are the most common type found in blood, lymph, and interstitial fluid -These are the major antibodies that help to destroy invading microbes -IgG antibodies also cross the placenta and defend the developing fetus against disease -IgA antibodies are secreted onto the surfaces of the digestive and respiratory tracts and into saliva and breast milk -IgA antibodies help to combat invaders entering via the mouth and nasal passages -They provide temporary defenses for nursing infants whose immune systems have not yet fully developed -IgE antibodies are responsible for allergic reactions -Antibodies serve two functions in the adaptive immune response -Recognizing foreign antigens and triggering the response against invaders -Helping to destroy the invading cells or molecules that bear antigens -T-cell receptors are found on the surfaces of T cells -Every T cell produces T-cell receptors that differ from those of all other T cells -Variable regions, which form highly specific binding sites for antigens, protrude from the cell surface

Most medical treatments for cancer depend on selectively killing cancerous cells

-Medical care for most cancers still relies on early detection and the traditional treatments of surgery, radiation, and chemotherapy -Surgically removing the tumor is the first step in treating many cancers, but it can be difficult to remove every bit of cancerous tissue -Tumors can be bombarded with radiation, which can destroy even microscopic clusters of cancer cells by disrupting their DNA, thus preventing cell division -Neither surgery nor radiation is effective against cancer that has spread throughout the body -Chemotherapy is commonly used to supplement surgery or radiation or to combat cancers that cannot be treated any other way -Chemotherapy drugs attack the machinery of cell division, so they are somewhat selective for cancer cells, which divide more frequently, but inevitably also kill some healthy, dividing cells

Innate immune response

-Nonspecinternal defenses: If the external barriers are breached, the innate immune response swings into action -Some white blood cells ific engulf foreign particles or destroy infected cells -Chemicals released by damaged body cells and proteins released by white blood cells trigger inflammation and fever -non specific -imediate invertebraes and vertebraes

The innate immune response nonspecifically combats invading microbes

-Pathogens that penetrate the external barriers encounter three types of nonspecific innate immune responses -Protection by white blood cells -The inflammatory response -Fever -Phagocytes and natural killer cells destroy invading microbes -The body has a standing army of white blood cells, or leukocytes, many of which are specialized to attack and destroy invading cells -One brigade, collectively called phagocytes, ingests foreign invaders and cellular debris by phagocytosis -Three important types of phagocytes are: -Macrophages -Neutrophils -Dendritic cells -These cells travel within the bloodstream, ooze through capillary walls, and patrol the body's tissues, where they consume bacteria and other foreign substances that have penetrated the skin or mucous membranes -Nonspecific defense against viruses is the job of another type of leukocyte, called the natural killer cell -Viruses enter body cells and use the cells' own metabolism to manufacture more viruses -Natural killer cells destroy virus-infected cells -Killing infected cells before the viruses have had enough time to reproduce and spread to other cells can stop viral infections before they do damage to the body as a whole -The surfaces of normal body cells display a set of proteins, collectively called the major histocompatibility complex (MHC), allowing natural killer cells to distinguish virus-infected cells from healthy cells -MHC proteins differ from species to species and, in fact, differ from individual to individual within a species -Most cancerous cells have missing or altered MHC proteins

The adaptive immune system distinguishes self from non-self

-The cells of the body manufacture thousands of complex molecules that can stimulate immune responses in other people's bodies -This is why transplants are often rejected -If the immature immune cells contact antigens that bind to their antibodies or T-cell receptors, they undergo apoptosis, or programmed cell death, in which they essentially commit cellular suicide -Therefore, the immune system distinguishes self from non-self by retaining only those immune cells that do not respond to the body's own molecules -Why don't your body's antigens arouse your own immune system? -Two important mechanisms normally prevent self-immunity -The continuous presences of the body's own antigens during immune cell development -The modulation of the immune response by regulatory T cells -When B and T cells first form in the bone marrow, they can bind antigens, but they are not yet able to trigger an immune response -If these immature cells bind antigens, they undergo apoptosis, or programmed cell death -Almost all B and T cells that happen to produce "self-reactive" antibodies or T-cell receptors are eliminated before they mature -T-cell receptors that can only bind foreign antigens usually do not encounter those antigens while they are still in development -These "foreign-reactive" cells survive, mature, and can trigger an immune response -Not all self-reactive B and T cells are eliminated in this way -One of the functions of regulatory T cells is to prevent any remaining self-reactive lymphocytes from attacking the body's own cells -The benefit to having millions of B and T cells is that almost any invader will provoke an adaptive immune response -The drawback is that there will be very few immune cells that can recognize any given invader, and a handful of cells isn't enough to kill the invaders immediately -It usually takes 1 to 2 weeks to mount a good immune response to the first exposure to an invading microbe, as the responding cells multiply and differentiate

How Does the Body Defend Itself Against Disease?

-The environment teems with microbes, which include microscopic living organisms such as bacteria, protists, and many fungi and viruses, which are usually not considered to be alive -Some microbes are pathogens, a term derived from Greek words meaning "to produce disease" Pathogens reproduce and seek new hosts -Most microbial diseases, such as cholera, measles, tetanus, and chicken pox, have infected people for hundreds or even thousands of years -Viruses in the news include -HIV -Ebola virus -We are also endangered by deadly, often new strains of bacteria -Staphylococcus aureus bacteria ("staph") occur frequently on the skin and in the nasal passages, but some strains cause fatal toxic shock syndrome or prolonged infections if they penetrate through the skin or mucous membranes

How Do Nonspecific Defenses Function?

-The ideal defenses are barriers that prevent invaders from entering the body in the first place -If these barriers are breached, however, the body has several nonspecific methods of killing a wide variety of invading microbes -The skin and mucous membranes form nonspecific external barriers to invasion -The first line of defense consists of the surfaces with direct exposure to the environment The skin -The mucous membranes of the digestive, respiratory, and urogenital tracts -The skin, its secretions, and harmless microbes reduce invasion of pathogens -The outer surface of the skin consists of dry, dead cells filled with tough proteins that do not allow microbes to obtain the water and nutrients they need to survive -The secretions from sweat and sebaceous glands contain natural antibiotics, such as lactic acid, that inhibit the growth of many bacteria and fungi -Mucus, antibacterial proteins, and ciliary action defend the mucous membranes against microbes -Mucous membranes deploy several defenses against infection -First, mucous membranes secrete mucus, which traps microbes that enter the nose or mouth -Mucus contains proteins, including lysozome, which kills bacteria by digesting their cell walls, and defensin, which makes holes in bacterial plasma membranes -Finally, cilia on the membranes sweep up the mucus, microbes and all, until it is either coughed or sneezed out of the body or is swallowed -If microbes are swallowed, they enter the stomach, where they encounter protein-digesting enzymes and extreme acidity; both are often lethal to them -Intestines contain bacteria that are harmless to people but secrete substances that destroy invading bacteria -In females, acidic secretions and mucus help protect the vagina -Fluids released by the body, including tears, urine, diarrhea, and vomit, help expel invaders

AIDS is an acquired immune deficiency disease

-The most common immunodeficiency disease is acquired immune deficiency syndrome (AIDS) -AIDS is caused by human immunodeficiency viruses (HIV) that undermine the immune system by infecting and destroying helper T cells, which stimulate both the cell-mediated and humoral immune responses -HIV enters a helper T cell and hijacks the cell's metabolic machinery, forcing it to make more viruses, which then emerge, taking an outer coating of T-cell membrane with them -Early in the infection, as the immune system fights the virus, the victim may develop a fever, rash, muscle aches, headaches, and enlarged lymph nodes -After several months, the rate of viral replication slows -Early in the infection, as the immune system fights the virus, the victim may develop a fever, rash, muscle aches, headaches, and enlarged lymph nodes -After several months, the rate of viral replication slows -Helper T-cell levels continue to decline, and eventually the immune response becomes too weak to overcome routine infections -At this time, the person is considered to have AIDS -The life expectancy for untreated AIDS victims is 1 to 2 years -Several drugs can slow down the replication of HIV and thereby slow the progress of AIDS -Some HIV-positive individuals receiving the best medical care might now live out a normal life span -Because HIV cannot survive for long outside the body, it is transmitted only through direct contact of an infected person's broken skin, mucous membranes, or virus-laden body fluids, including blood, semen, vaginal secretions, and breast milk -HIV can be spread by sexual activity, by sharing needles with intravenous drug users, or through blood transfusions -A woman infected with HIV can transmit the virus to her child during pregnancy, childbirth, or breastfeeding -no vaccine exists that is effective against HIV

Spleen

-The spleen is a fist-sized organ located on the left side of the abdominal cavity, between the stomach and diaphragm -The spleen filters blood, exposing it to white blood cells that destroy microbes and aged red blood cells

Tonsils

-The tonsils are located in a ring around the pharynx (the uppermost part of the throat) -They are ideally located to sample microbes entering the body through the mouth -Macrophages and other white blood cells in the tonsils directly destroy many invading microbes and often trigger an adaptive immune response

A large number of different proteins are involved in the adaptive immune response

-There are dozens of different cytokines that are used for communication between cells -Their functions are as varied as stimulating cell division in lymphocytes during the immune response and stimulating the inflammatory response -Antibodies, proteins produced by B cells and their offspring, help the immune system to recognize invading microbes and destroy them -Complement proteins are mostly synthesized by the liver and circulate in the blood plasma -They assist the immune system in killing invading microbes

Immune deficiency diseases occur when the body cannot mount an effective immune response

-There are two very different disorders in which the immune system cannot combat routine infections -About 1 in 500 people has some type of genetic immune deficiency -Much more frequent are acquired immune deficiencies that arise during a person's lifetime -There are many causes of acquired immune deficiencies, including radiation, chemotherapy, immune suppressive drugs, diabetes, leukemia, and pathogenic microbes -Severe combined immune deficiency is an inherited disorder -About 1 in 60,000 children is born with severe combined immune deficiency (SCID), which occurs when any of several genetic defects cause few or no immune cells to be formed -A child with SCID may survive the first few months after birth, protected by IgG and IgA antibodies acquired from the mother during pregnancy or in her milk -Once these antibodies are lost, common infections can prove fatal because the child, lacking an immune system, cannot generate an effective immune response -One form of therapy is to transplant bone marrow from a healthy donor into the child

Vertebrate animals have three major lines of defense

-Vertebrates have evolved three major forms of protection against disease 1. Nonspecific external barriers prevent most disease-causing microbes from entering the body -The anatomical structures include skin and cilia -Secretions include tears, saliva, and mucus -These barriers cover the external surfaces of the body and line body cavities that open to the external environment, including the respiratory, digestive, and urogenital tracts 2. Nonspecific internal defenses: If the external barriers are breached, the innate immune response swings into action -Some white blood cells engulf foreign particles or destroy infected cells -Chemicals released by damaged body cells and proteins released by white blood cells trigger inflammation and fever 3. Specific internal defenses, the final line of defense, comprise the adaptive immune response, in which immune cells selectively destroy the specific invading toxin or microbe and then "remember" the invader, allowing a faster response if it reappears in the future

Vaccination can prevent or treat some types of cancers

-Viruses cause some cancers of the liver, mouth, throat, and penis; some types of leukemia; and probably all cases of cervical cancer -In the United States, preventive vaccines have been approved that protect against the virus that causes hepatitis B, which triggers some cases of liver cancer, and against the two types of human papilloma viruses (HPV) that cause most cases of cervical cancer -Some of the vaccines would provide a patient with antigens commonly found on cells of the type of cancer that the patient has -The antigens would be enhanced in various ways to boost the patient's immune response against them -Other treatment vaccines consist of antigens from a patient's own tumor cells -Another approach is to take antigen-presenting dendritic cells from a patient, expose them to antigens from cancer cells, and force them to multiply rapidly in culture

Antibiotics

Antibiotics are chemicals that help combat infection by killing or interfering with the multiplication of bacteria, fungi, or protists

Antiviral drugs

Antiviral drugs are now available that target different stages of the viral cycle of infection, including attachment to a host cell, replication of viral parts, assembly of new viruses within the host cell, and the release of these viruses to infect more body cells

B cells and T cells

B cells and T cells are two types of lymphocytes that arise from dividing stem cells in the bone marrow

Variable region

Both heavy and light chains consist of a variable region, which differs among individual antibodies, and a constant region, which is the same in all antibodies of the same type

Cell-mediated immunity is produced by cytotoxic T cells

Cell-mediated immunity is produced by cytotoxic T cells, which attack virus-infected body cells and cells that have become cancerous -Though complex, the process works like this: -When a cell is infected by a virus, some pieces of viral proteins are brought to the surface of the infected cells and "displayed" on the outside of the plasma membrane -When a cytotoxic T cell with an appropriate matching T-cell receptor binds to a viral antigen, the cytotoxic T cell passes through pores, killing the infected cell -If the infected cell is killed before the virus has finished multiplying, then no new viruses are produced, and the viral infection cannot spread to other cells -Cancer cells often display unusual proteins on their surfaces that cytotoxic T cells recognize as foreign and can be killed by the same mechanism

Humoral immunity

Humoral immunity is provided by B cells and the antibodies that they secrete into the bloodstream

Fever

If invaders breach these defenses and mount a full-blown infection, they may trigger a fever, which slows down microbial reproduction and enhances the body's own fighting abilities

Lymphocytes

Lymphocytes are specialized white blood cells that are unique to the adaptive immune response

Natural killer cell

Nonspecific defense against viruses is the job of another type of leukocyte, called the natural killer cell

Adaptive immune response

Specific internal defenses, the final line of defense, comprise the adaptive immune response, in which immune cells selectively destroy the specific invading toxin or microbe and then "remember" the invader, allowing a faster response if it reappears in the future -Specific for particular microbes -Delay of several days -Enhanced response -Vertebras only

The adaptive immune response is produced by interactions among several types of cells

The adaptive immune system includes several types of leukocytes: -Macrophages -Dendritic cells -Lymphocytes -Macrophages and dendritic cells play a role in both the innate and adaptive immune responses -Lymphocytes are specialized white blood cells that are unique to the adaptive immune response -B cells and T cells are two types of lymphocytes that arise from dividing stem cells in the bone marrow -The adaptive immune system is distributed throughout the body with concentrations of cells in specific locations -These locations include bone marrow, the vessels of the lymphatic system, the lymph nodes, the thymus, the spleen, and patches of specialized connective tissue such as the tonsils -The human body contains about 500 lymph nodes scattered along the lymph vessels -Lymph nodes contain masses of macrophages and lymphocytes lining narrow passages through which lymph flows -The thymus is located beneath the breastbone, slightly above the heart, and is essential for development of T cells -The spleen is a fist-sized organ located on the left side of the abdominal cavity, between the stomach and diaphragm -The spleen filters blood, exposing it to white blood cells that destroy microbes and aged red blood cells -The tonsils are located in a ring around the pharynx (the uppermost part of the throat) -They are ideally located to sample microbes entering the body through the mouth -Macrophages and other white blood cells in the tonsils directly destroy many invading microbes and often trigger an adaptive immune response

Leukocytes

The body has a standing army of white blood cells, or leukocytes, many of which are specialized to attack and destroy invading cells

Microbes

The environment teems with microbes, which include microscopic living organisms such as bacteria, protists, and many fungi and viruses, which are usually not considered to be alive

Mast cells

The inflammatory response begins when damaged cells release chemicals that cause certain cells in the connective tissue, called mast cells, to release histamine

Autoimmune disease

The result is an autoimmune disease in which the immune system attacks a component of one's own body

the major histocompatibility complex (MHC)

The surfaces of normal body cells display a set of proteins, collectively called the major histocompatibility complex (MHC), allowing natural killer cells to distinguish virus-infected cells from healthy cells

Thymus

The thymus is located beneath the breastbone, slightly above the heart, and is essential for development of T cells