07.06 Immune System

histamines

. These histamines increase the blood flow to the infected area, causing the area to swell.

antibodies

A protein that either attacks antigens directly or produces antigen-binding proteins

lymphocytes

A type of small white blood cell produced in the lymphoid tissue, including T cells and B cells.

pathogens

A virus or microorganism (bacteria, fungi, and protists) that causes disease in its plant or animal host.

fever

Another nonspecific response to an infection is an increase in body temperature called a fever. The increase in temperature may slow down or destroy some pathogens, but it also serves to speed up some of the mechanisms in the body's defense against the infection.

B cells circulate through the blood stream, patrolling for invading pathogens. B cells have antibodies embedded on their surface, and the unique shape of the antibodies enables them to recognize and attach to one specific type of antigen.

B cells circulate through the blood stream, patrolling for invading pathogens. B cells have antibodies embedded on their surface, and the unique shape of the antibodies enables them to recognize and attach to one specific type of antigen.

Bacteria

Bacteria are single-celled organisms that are shaped like rods, spheres, or spirals. Not all bacteria are harmful; less than 1 percent of the bacteria on Earth cause disease. You have some bacteria in your body that benefit you by helping you digest food, providing you with nutrients, and destroying some disease-causing microorganisms. Bacteria that cause disease do so by producing toxic chemicals that damage your cells and make you ill. Bacteria cause diseases like tuberculosis, strep throat, and urinary tract infections.

antimicrobial

Capable of destroying or inhibiting the growth of disease-causing pathogens.

Cell-Mediated Immunity

Cell-mediated immunity defends the body against invading pathogens that attack within body cells. This type of immunity uses T cells and does not involve antibodies.

If you wanted to investigate to determine which part of the immune system was responding to an infection, what changes to the human body would you identify and measure?

Changes to mucus production as well as changes in the skin can indicate an initial external nonspecific defense of the immune system to an infection. Inflammation of an area indicates an increase in measurable histamines which indicates an internal non-specific response to the infection. A fever is a sudden increase in body temperature that is also measurable and an internal non-specific response. White blood cell counts (measurable by a blood test) can also indicate an initial internal response to infection. Humoral (B cells) and cell-mediated immunity (t-cells) can also be measured by a blood test and represents specific defense mechanisms against an infection.

disinfect

Cleanse in order to destroy or prevent the growth of disease-carrying microorganisms.

Both are destructive and disrupt the regular functions of their hosts.

Computer viruses can make your computer freeze up or function incorrectly, and can even delete important information. A virus that infects a human disrupts the normal functions of the cells or entire systems that it invades. Cells are usually destroyed after they are used to replicate the virus.

Cytotoxic T cells play an important role in the immune system, destroying infected body cells or cancerous cells. However, this type of immune response can be harmful when a person receives an organ transplant. To prevent organ rejection, doctors try to find organ donors with similar chemical markers on their body cells. In addition, organ recipients also take medications that suppress the cell-mediated immune response in order to prevent cytotoxic T cells from damaging or destroying the transplanted tissue or organ.

Cytotoxic T cells play an important role in the immune system, destroying infected body cells or cancerous cells. However, this type of immune response can be harmful when a person receives an organ transplant. To prevent organ rejection, doctors try to find organ donors with similar chemical markers on their body cells. In addition, organ recipients also take medications that suppress the cell-mediated immune response in order to prevent cytotoxic T cells from damaging or destroying the transplanted tissue or organ.

Summary

For a pathogen, such as a bacteria or virus, to infect your body, it must go through several lines of defense. The nonspecific defenses include the external protection of skin and mucous membranes, as well as internal defenses such as phagocytic white blood cells, inflammation, and fever. Your immune system also provides specific defenses that produce antibodies and lymphocytes that fight specific pathogens. In addition, your immune system produces memory B and T cells that allow for a much more rapid response if the same pathogen ever attacks your body again. Vaccines, medications, and antiseptics can be used to assist the immune system, as can preventative measures such as washing your hands thoroughly and avoiding contaminated food and water.

Fungi

Fungi include a large range of eukaryotic organisms such as yeast, mold, and mushrooms. Many of these organisms are not harmful to humans, and we eat quite a few of them. However, some fungi do cause illness. Candida is a type of yeast that can cause infections of the mouth and throat in infants and people taking antibiotics. Other fungi can cause skin problems such as ringworm and athlete's foot.

inflammatory response

Have you ever had an infected splinter that becomes red and swollen? This is an example of the body's inflammatory response, which occurs when invading pathogens trigger the body to release chemicals called histamines.

Both can spread quickly, and often inadvertently.

Have you ever received a suspicious email from a friend, later finding out that your friend didn't even know that his email account was sending the contaminated messages to everyone in his address book? In a similar way, humans may not know that they are infected with a virus. By the time symptoms of the disease appear, that person has already spread the infectious virus to others.

Humoral Immunity

Humoral immunity is activated when antibodies recognize and bind to antigens on the surface of an invading pathogen.

Controlling Pathogens

Medical technology can be used to assist the immune system. Antibiotics are medications that can be used to kill bacteria, but they are not effective against viruses like a cold or flu. Antiviral drugs can be used to slow down the spread of certain viral infections by inhibiting their ability to invade cells or to multiple inside the cells. Antiseptics are antimicrobial substances applied to skin or living tissue to reduce the possibility of infection. Alcohols, such as ethanol and isopropanol are rubbed on the skin to disinfect it before injections are given. Boric acid is an antiseptic used in eye washes, cold sore treatments, and yeast infection treatments. Hydrogen peroxide is sometimes used in household first aid kits to clean and disinfect cuts and scrapes. However, this can be a harsh treatment that can cause scar formation, so washing wounds with soap and water or saline solution is now recommended. The misuse or overuse of medications has led to an increase in the occurrence of diseases that were once considered under control. This is because many strains of bacteria have evolved a resistance to the commonly used antibiotics, antiseptics, and medications. The bacteria that are not killed by the exposure to antiseptics or antibiotics survive to reproduce, producing an increasing population of bacteria with a resistance to those medications.

Once a B cell's antibody binds to a pathogen's antigen, T cells stimulate the B cell to grow and divide rapidly. This division produces two types of B cells: plasma cells and memory B cells. Sample image showing the two types of cells created: label the ones on the left "plasma cells" and the ones on the right "memory B cells".

Once a B cell's antibody binds to a pathogen's antigen, T cells stimulate the B cell to grow and divide rapidly. This division produces two types of B cells: plasma cells and memory B cells. Sample image showing the two types of cells created: label the ones on the left "plasma cells" and the ones on the right "memory B cells".

Nonspecific Defenses

Our bodies have a series of defenses that help protect against disease-causing pathogens and other foreign substances.

Pathogens

Pathogens are infection-causing agents. You can find pathogens in the air, on food, in water, in the soil, and on just about every other surface. Your body's immune system has a variety of ways to defend against this variety of pathogens. Infectious agents come in a variety of shapes and sizes. Categories include:

Plasma cells produce and release antibodies into the bloodstream to be carried throughout the body. The antibodies bind to any corresponding antigens that they encounter. A healthy adult can produce around 10 billion different types of antibodies, each able to bind to a different type of antigen. When this binding occurs, the plasma cells act as signals to proteins and cells that attack and destroy the invading pathogen.

Plasma cells produce and release antibodies into the bloodstream to be carried throughout the body. The antibodies bind to any corresponding antigens that they encounter. A healthy adult can produce around 10 billion different types of antibodies, each able to bind to a different type of antigen. When this binding occurs, the plasma cells act as signals to proteins and cells that attack and destroy the invading pathogen.

Protozoa

Protozoa are single-celled organisms that hunt and gather other microbes for food. Protozoa often spend at least part of their life cycle outside of human or animal hosts. They can invade people's bodies through contaminated food or water to cause diseases such as toxoplasmosis and giardia, while malaria is transmitted by mosquitoes.

External

Skin covers the body's surface and forms a physical barrier that protects the systems inside the body. Very few pathogens can penetrate the layer of dead cells on the skin's surface. The external defense system also uses chemical defenses to deter pathogens from infecting the skin or entering the body. For example, secretions from the skin's oil and sweat glands are acidic, which is an unwelcoming environment for many bacteria and microorganisms. Saliva, mucus, and tears help prevent pathogens from entering the body through the mouth, nose, and eyes. These secretions contain enzymes that break down bacterial cell walls, another example of a chemical defense. The mucus in your nose and throat also traps many pathogens in order to prevent them from entering the lungs or digestive tract.

Let's Review

The body has systems of specific and nonspecific defenses to protect itself against invading viruses, bacteria, fungi, and other pathogens. The table below summarizes the different mechanisms involved in each line of defense.

Specific Defenses: The Immune System

The body's third line of defense, the immune system, responds to specific types of pathogens that invade the body. This line of defense comes into play at the same time as the internal nonspecific defenses, and the two lines of defense work together to protect the body. The functions of the immune system include production of specific defense proteins called antibodies as well as the participation of white blood cells called lymphocytes. A healthy immune system recognizes chemical markers on the body's own cells and proteins. These chemical markers are determined by a person's genetic coding and each individual's chemical markings are unique. This is important because it ensures that the destructive powers of the immune system are not used against the body's own cells, only against foreign substances. When the immune system recognizes that an invader does not have the body's chemical markers, it uses cells and chemical defenses to attack them. Molecules called antigens can be found on the outer surface of bacteria, viruses, parasites, pollen, insect venom, and transplanted tissues. When the immune system detects the antigens on the surface of the invading substance instead of the body's own chemical markers, it triggers an immune response. Each antigen has a unique molecular shape that stimulates production of a corresponding antibody. The antibodies are specialized proteins that bind to the corresponding antigen, like fitting two puzzle pieces together. This marks the foreign substance to be destroyed by white blood cells called lymphocytes. The white blood cells involved in the specific defenses of the immune system are primarily B lymphocytes (B cells) and T lymphocytes (T cells). Both are produced in red bone marrow, but B cells also mature in the blood marrow while T cells mature in the thymus, an endocrine gland. The B cells and T cells are constantly patrolling the body, in search of antigens. Each type of B cell and T cell is capable of recognizing and destroying one type of antigen. B cells have embedded antibodies, so they are able to discover antigens in body fluids. T cells attack pathogens that have invaded body cells. The specific immune response can be divided into two main types of action: humoral immunity and cell-mediated immunity.

Did you know?

The concept of acquired immunity was recognized more than 2,400 years ago by Thucydides of Athens. He recognized that people who recovered from the plague were able to help care for those who were sick or dying from the plague without getting sick again, because the plague never seemed to attack the same person twice. More than 200 years ago, the English physician Edward Jenner observed that milkmaids who had once suffered from a mild case of cowpox did not seem to catch smallpox. He wondered if people could be deliberately infected with cowpox in order to protect them from the deadly smallpox, and he experimented with early vaccines. The word vaccine actually comes from the Latin word vacca, meaning "cow," in honor of Jenner's work.

Active and Passive Immunity

The immune system uses memory cells to remember antigens it has encountered in the past in order to react against them more rapidly and effectively on future exposures. This is called an active immunity, because it involves a response by a person's own immune system. An active immunity that results from a person acquiring memory cells after recovering from an infectious disease is a naturally acquired active immunity. Deliberate exposure to an antigen through a vaccine results in an artificially acquired active immunity. Vaccines may be living but weakened microorganisms, inactivated bacterial toxins, or killed microorganisms. They no longer cause disease, but still act as antigens to stimulate an immune response. Vaccines allow a person to develop memory cells that will allow the immune system to act quickly if they ever encounter the actual pathogen. Antibodies produced by animals or other individuals can sometimes be introduced into a person's blood, resulting in a passive immunity. This type of immunity will only last a short time; the person's own immune system will eventually attack and destroy the foreign antibodies. Passive immunity can be naturally acquired when antibodies are passed from a pregnant woman to the fetus through the placenta, or to an infant through a mother's breast milk. This provides a newborn infant with a temporary immunity to some diseases for a few weeks or months. Antibodies from people or animals that have an active immunity to a disease can be injected into patients who need immediate immunity. For example, rabies victims are injected with antibodies from people who have already been vaccinated against rabies. This provides an instant immunity, which is important because rabies is a deadly disease that progresses rapidly. This artificially acquired passive immunity will last a few weeks, which gives the patient's own immune system time to produce antibodies to fight the rabies infection.

phagocytes

The increase of blood flow to an infected area brings more white blood cells, which move from the blood vessels into the infected tissue. Many of these white blood cells are phagocytes, cells that engulf and destroy invading bacteria cells.

The memory T cells remain in the body even after the infection is gone in order to help the body respond even more quickly if it is invaded by the same type of pathogen in the future.

The memory T cells remain in the body even after the infection is gone in order to help the body respond even more quickly if it is invaded by the same type of pathogen in the future.

What indications would let you know that the immune system has effectively fought off an infection?

The most obvious indicator of an effective immune response is the body's return to homeostasis, such as no inflammation, no mucus production, and normal body temperature.

The now numerous helper T cells activate cytotoxic T cells and produce memory T cells. The cytotoxic T cells recognize the antigen markings on the infected cells. They insert cytotoxins into the infected cells to destroy them in order to prevent the infection from spreading.

The now numerous helper T cells activate cytotoxic T cells and produce memory T cells. The cytotoxic T cells recognize the antigen markings on the infected cells. They insert cytotoxins into the infected cells to destroy them in order to prevent the infection from spreading.

Internal

The pathogens that make it past the external defenses encounter a second line of nonspecific defense inside the body. The mechanisms in this second line of defense include the inflammatory response, white blood cells, and fever. Have you ever had an infected splinter that becomes red and swollen? This is an example of the body's inflammatory response, which occurs when invading pathogens trigger the body to release chemicals called histamines. These histamines increase the blood flow to the infected area, causing the area to swell. The increase of blood flow to an infected area brings more white blood cells, which move from the blood vessels into the infected tissue. Many of these white blood cells are phagocytes, cells that engulf and destroy invading bacteria cells. The presence of an infection in the body can also increase the production of white blood cells from inside bone marrow. Sometimes doctors check the white blood cell count in a patient in order to detect the presence of a severe infection. Another nonspecific response to an infection is an increase in body temperature called a fever. The increase in temperature may slow down or destroy some pathogens, but it also serves to speed up some of the mechanisms in the body's defense against the infection.

The plasma cells die once an infection is gone, but some memory B cells remain. If the same type of pathogen ever enters the body again in the future, the memory cells are able to respond more rapidly than the B cells in the primary response. Memory B cells can produce new plasma cells very quickly, which then bind to the pathogens and signal for their destruction.

The plasma cells die once an infection is gone, but some memory B cells remain. If the same type of pathogen ever enters the body again in the future, the memory cells are able to respond more rapidly than the B cells in the primary response. Memory B cells can produce new plasma cells very quickly, which then bind to the pathogens and signal for their destruction.

What investigative procedures would you follow to determine if a non-specific immune response was taking place in a test subject?

There are many ways a student could investigate immune responses. For example, a student could measure the amount of mucus production, inflammation in an area, or fever over a specific number of days and at specific times. Once the data was collected, the student could use it to determine when and how the immune system responded to a specific infection.

Viruses

Viruses are nonliving infectious particles made up of viral genes enclosed in a protein capsule. They can only replicate within a host cell, which they identify with a lock and key fit between the proteins on the outside of their capsules and specific molecules on the surface of the cell. Most viruses can only infect a limited range of host cells, which means that viruses in some plants and animals are not able to infect humans. Some viruses are able to infect more than one species, such as monkey pox, SARS, and swine flu. Other viruses include common cold, flu, measles, smallpox, genital herpes, and HIV.

resistance

When a bacteria is able to survive exposure to an antibiotic.

When a body cell is invaded by a pathogen the cell's membrane displays a portion of the pathogen's antigen.

When a body cell is invaded by a pathogen the cell's membrane displays a portion of the pathogen's antigen.

When circulating helper T cells detect this signal on the infected cells, they divide.

When circulating helper T cells detect this signal on the infected cells, they divide.

When you have completed this lesson, you should be able to: identify the body systems that protect from pathogens summarize how the cells of the immune system respond to pathogens identify specific and nonspecific immune responses and the body systems that produce them identify methods used to control pathogens explain how vaccines artificially produce acquired immunity

When you have completed this lesson, you should be able to: identify the body systems that protect from pathogens summarize how the cells of the immune system respond to pathogens identify specific and nonspecific immune responses and the body systems that produce them identify methods used to control pathogens explain how vaccines artificially produce acquired immunity

Your computer may have security software that helps protect it from a variety of computer viruses being passed along through cyberspace. There are also things that you can do, like not clicking on those suspicious emails or pop-ups, to help keep your computer safe. Similarly, your body has several mechanisms that protect it from many of the viruses and other infectious agents it encounters every day. "What are some precautions you can take to help keep yourself healthy," and "how does the body respond to viruses and pathogens?" These are the driving questions of this lesson.

Your computer may have security software that helps protect it from a variety of computer viruses being passed along through cyberspace. There are also things that you can do, like not clicking on those suspicious emails or pop-ups, to help keep your computer safe. Similarly, your body has several mechanisms that protect it from many of the viruses and other infectious agents it encounters every day. "What are some precautions you can take to help keep yourself healthy," and "how does the body respond to viruses and pathogens?" These are the driving questions of this lesson.