What is the main role of the human immune system?
The immune system protects the body against bacteria, viruses, and other invading organisms or substances.
In other words, the immune system helps protect against foreign, often disease-causing agents.
A leukocyte, also known as a white blood cell, is a cell involved in immune function.
Leukocytes are a broad category of cells, including neutrophils, monocytes, and lymphocytes, among others.
Name the most abundant leukocyte found in the blood.
The most abundant leukocytes are neutrophils, which constitute 50-70% of all white blood cells by number.
As one of the first cell types to reach the site of an infection, neutrophils are the main component of pus. Like macrophages, they can perform phagocytosis.
A pathogen is a disease-causing organism. The purpose of the immune system is to protect against pathogens, foreign particles, and the body's own damaged cells.
Pathogens can include bacteria, viruses, and fungi.
What is the difference between innate and specific immunity?
Innate immunity provides a broad line of defense against foreign material. Its response to pathogens is general, not specific to the identity of the pathogen.
Specific immunity is highly specialized, using immunological memory of previous infections to respond to certain pathogens.
Macrophages, neutrophils, mast cells, and other cell types are involved in innate immunity. T and B lymphocytes are involved in specific immunity.
Give another name for innate immunity.
Innate immunity is also known as nonspecific immunity.
Other than the skin and mucous membranes, name three components of the innate immune response.
Three main components of the innate (nonspecific) immune response are:
- The inflammatory response
What large organ covers most of the body and serves as an early line of defense against pathogens?
Remember, the skin is technically an organ! Skin serves as an innate protective mechanism against many pathogens and foreign substances.
Which structures secrete a thick fluid that helps protect the digestive and respiratory tract against pathogens?
These membranes (or linings) secrete mucus, a protective fluid that can coat pathogens and foreign particles, trapping them in place. Mucus often contains enzymes that act to damage microbes (bacteria and viruses).
What enzyme is found in tears and catalyzes the breakdown of bacterial cell walls?
Specifically, lysozyme catalyzes the breaking of glycosidic linkages within peptidoglycan molecules. This role is part of the innate immune system.
Which of the following is not directly involved in the innate immune response?
- B lymphocytes
- Mucus in the respiratory tract
B lymphocytes do not play a major role in innate immunity. The other choices all provide a first line of defense against a wide variety of pathogens.
B lymphocytes, on the other hand, produce antibodies. These products are highly specialized to recognize certain antigens, and form a large part of specific immunity.
What is phagocytosis?
Phagocytosis is the engulfment of a foreign particle by an immune cell, or phagocyte. The particle is taken up in a vesicle and can then be degraded.
This process can often involve chemotaxis, a form of movement in which a cell is drawn toward or away from specific chemical substances.
Which of the following cells cannot perform phagocytosis?
Erythrocytes cannot perform phagocytosis. Erythrocytes are red blood cells, which do not serve a major function in the immune system.
Neutrophils, monocytes, and macrophages all perform phagocytosis as an important part of innate immunity.
Describe three main effects of the inflammatory response.
- Capillary permeability increases, allowing immune cells to access the infected site. This results in redness and swelling.
- The infected area becomes warm.
- The infected area is often painful due to swelling and the presence of certain chemicals.
Diphenhydramine, an allergy medication, functions as an antihistamine. Which immune response is likely to be inhibited by the administration of diphenhydramine?
Diphenhydramine will inhibit the inflammatory response.
Histamine is a chemical that functions as part of the inflammatory response. Specifically, it increases capillary permeability and can lead to many common allergy symptoms.
Which type of pathogen do interferons combat?
Interferons, a subtype of cytokines, are generally associated with viral infection. However, they can also be activated by bacterial infection or cancerous growth.
As signaling molecules, interferons do not directly kill infected cells; instead, they activate surrounding immune cells.
In what part of the body are lymphocytes synthesized?
Lymphocytes (B and T cells) are synthesized in the bone marrow.
B lymphocytes also remain in the bone marrow to mature, while T lymphocytes move to the thymus for maturation.
Give another name for specific immunity.
Specific immunity is also known as adaptive or acquired immunity.
Which of the following is not directly involved in the specific immune response?
- T lymphocytes
- B lymphocytes
Macrophages do not play a direct role in specific, or acquired, immunity.
Specific immunity involves cells that specialize to recognize and attack a limited class of antigens. In contrast, macrophages phagocytose a wide variety of pathogens and foreign particles.
Name the two types of specific immunity.
The two types of specific immunity are cell-mediated and humoral immunity.
A certain virus inhibits the functioning of cytotoxic T cells. Which type of specific immunity would be limited in this case?
Cell-mediated immunity would be inhibited.
Cell-mediated immunity involves cytotoxic T lymphocytes, as well as other immune cells. Specifically, it allows the destruction of body cells that have been marked for destruction after viral infection or other damage.
Which type of specific immunity involves B lymphocytes?
Humoral immunity involves antibodies, which are produced by B lymphocytes to recognize specific bloodborne antigens. It also involves the differentiation of plasma and memory B cells upon exposure to a pathogen.
An antigen is a substance that causes an immune response. Specifically, antigens are markers that can be recognized by antibodies.
The surface proteins that determine blood type (A and B) are examples of antigens.
An antibody is an immune protein that recognizes a specific, potentially harmful antigen or class of antigens. Antibodies are produced by B lymphocytes.
For the AP Biology exam, be sure to avoid confusion between antibodies and antigens. Antigens are attacked, while antibodies do the attacking.
What word is synonymous with the term "antibody?"
Antibodies are also known as immunoglobulins.
Immunoglobulins are abbreviated "Ig." Though you do not need to know the function of each type, five types of immunoglobulin exist in human blood: IgM, IgE, IgG, IgD, and IgA.
Label the following parts of the antibody shown below: heavy chain, light chain, constant region, variable region, antibody binding sites.
Name three ways that antibodies hinder and facilitate the destruction of pathogens.
- Antibodies activate the complement system, a protein cascade that promotes immune function.
- In a process called agglutination, antibodies bind to antigens on an invading cell's surface. This limits the pathogen's movement and keeps it from entering body cells.
- Antibodies perform opsonization, which alerts phagocytes to engulf the pathogen.
In class, a student mentions that antibodies function by directly lysing foreign cells. What is wrong with this explanation?
Antibodies do not directly kill pathogens; they simply bind to and mark the invading cell for destruction.
In contrast, phagocytes and killer T cells are capable of destroying pathogens.
What immune product is shown here, and what is its function?
This molecule is an antibody.
Antibodies are produced by B lymphocytes. They play a major role in specific, or acquired, immunity by recognizing and binding specific antigens.
Which two types of B lymphocytes arise from naive B cells?
Naive, or undifferentiated, B cells can differentiate into plasma and memory B cells.
Upon exposure to a pathogen, the majority of cells produced are plasma B lymphocytes; these cells produce antibodies to target the invader. In contrast, memory B cells remain in the blood and activate a faster response in the case of a second exposure to the same antigen. Note that memory T cells also exist.
A defect in a certain immune cell type results in a dramatic decrease in the production of antibodies. Which cell type is likely affected?
This defect likely affects B lymphocytes.
B lymphocytes act as a vital part of acquired immunity by producing protein products called antibodies.
Which theory explains how specific antibody-producing cells proliferate despite the enormous variety of these cells in the body?
An extremely diverse range of B cells are present in the body; as a result, a wide variety of antibodies can be produced. According to clonal selection, B cells specific for an antigen will be "cloned," or copied, after exposure. B lymphocytes that are specific for "self" tissues will be destroyed.
How does the speed of the primary immune response differ from that of the second, and subsequent, responses?
The primary immune response takes much longer, as B cells specific for the antigen in question have not differentiated.
A primary response can take 14 days or longer, while a secondary response can eliminate a pathogen in less than a day.
Name the two main types of T lymphocytes and describe their functions.
T lymphocytes are broadly classified into cytotoxic (killer) T cells and helper T cells.
Cytotoxic T cells directly bind damaged or infected cells that express certain antigens. They then kill the cell through the release of apoptosis-inducing factors. Helper T cells secrete cytokines that chemically facilitate B cell and cytotoxic T cell activity.
A lesser-known subtype of T lymphocyte plays a major role in counteracting autoimmune disease. What term describes this cell type?
These lymphocytes are called suppressor or regulatory T cells.
Suppressor T cells limit the activation and continuation of immune responses. This reduces the likelihood that the host's immune system will react against "self" tissues, or those of its own body.
Which immune cells are targeted by the human immunodeficiency virus (HIV)?
HIV infects and incapacitates helper T cells, possibly through interactions with the CD4 glycoprotein receptor.
As a result, HIV+ individuals have severely limited immune systems and are prone to a variety of infections.
What broad name is given to cell surface proteins that aid in T cell recognition?
The major histocompatibility complex (MHC)
MHC genes code for glycoproteins located on cell surfaces. In a process termed antigen presentation, they bind to antigens and display them for T cells to recognize. MHC proteins are divided into two main classes, MHC I and MHC II.
Describe the role of MHC I receptor proteins.
MHC I receptors bind to normal proteins that are produced within the cells of the body. When a cell becomes infected or cancerous, it triggers recognition as "non-self" and can be marked for destruction by a T cell.
Antigens presented by MHC I are recognized only by cytotoxic T cells that contain the CD8 surface protein.
Describe the role of MHC II receptor proteins.
MHC II receptors bind to foreign antigens that have been broken down by phagocytosis. When fragments of these antigens are presented on immune cells, helper T cells recognize a threat and can activate other immune responses.
Antigens presented by MHC II are recognized only by helper T cells that contain the CD4 surface protein.
A sample of normal human cells are found to be lacking MHC I receptors. What cell type(s) might this sample contain?
The sample must contain cells that lack nuclei, likely erythrocytes (red blood cells).
MHC I glycoproteins are present on every body cell, except for those that do not contain nuclei. These receptors allow T cells to recognize cells that are malfunctioning.
A sample of human cells is found to contain a significant number of MHC II receptors. What cell type(s) might this sample contain?
The sample must contain immune cells, specifically those that present antigens to CD4+ helper T cells.
Antigen-presenting immune cells include dendritic cells, B lymphocytes, and macrophages.
What name is given to an adverse inflammatory response to non-pathogenic material such as animal hair or pollen?
Allergies, or immune responses to typically harmless compounds, commonly occur when the inflammatory response is overactive.
Allergies are often treated with antihistamines, which counteract a main inflammatory chemical agent.
A deficiency in monocytes will likely lead to a lower-than-average number of what other type of cell?
Monocytes differentiate into macrophages, which are phagocytic cells that act as a part of the innate immune response.
What is the function of the spleen?
With regard to the immune system, the spleen produces and stores immune cells such as lymphocytes and monocytes. It also filters the blood, removing old or nonfunctioning red blood cells.
A main function of the spleen involves the engulfment and breakdown of red blood cells. With this in mind, which type of immune cell is likely highly active in this organ?
The spleen contains an especially high number of macrophages.
Since macrophages are phagocytic cells, they are generally active in organs where debris or damaged cells must be engulfed and destroyed.
What is the function of the thymus, and which hormone does it mainly secrete?
During infancy and childhood, the thymus serves as the site of T cell maturation. Specifically, it promotes the inactivation of T cells that would otherwise attack "self" tissues.
As part of this function, the thymus produces the peptide hormone thymosin.
If a man has type A+ blood, against which antigens will his immune system produce antibodies?
His immune system will produce antibodies against B antigens only.
Antibodies are produced against foreign antigens. Since the man's own blood cells contain A and Rh antigens on their surfaces, antibodies will not be produced to attack those markers.
If a man has type O- blood, which antigens are present on the surface of his own red blood cells?
No antigens are present.
An individual's blood type describes the antigens displayed on his or her red blood cells. Type A refers to A antigens, type B refers to B antigens, and type AB refers to both. Type O signifies the lack of either A or B antigens. Similarly, the "+" designation refers to the presence of the Rh antigen, and the "-" designation refers to its absence.
What occurs when a person is given a blood transfusion that contains foreign antigens?
In a process called hemagglutination, the recipient's antibodies cause the transfused blood to bind and clump together.
Though every cell contains antigens on its surface, the body tissues of a healthy individual are protected from attack by his or her own immune system. What name is given to these cells?
These cells are part of the self. Except in cases of autoimmune disorders, only nonself cells should provoke an immune response.
The process of distinguishing self from nonself occurs in the thymus during development. Immune cells that are specific to normal body tissues are isolated and destroyed before they can harm the individual.
What happens to an individual who suffers from an autoimmune disease?
The individual's immune cells attack his or her healthy tissue, causing a variety of damaging effects.
Though the exact causes of most autoimmune responses are unclear, a genetic component is often involved, and environmental factors may play a role.
Describe the general structure of the lymphatic system.
The lymphatic system is a network of vessels that transport a fluid called lymph. Lymph nodes, or small clusters of lymphatic tissue, are positioned along these vessels.
Other organs, such as the thymus and the spleen, also contain lymphoid tissue.
The lymphatic system serves what main function apart from its immune role?
The lymphatic system drains excess interstitial fluid from the tissues. After filtration through lymph nodes, this fluid is eventually returned to the bloodstream.
This activity minimizes edema, or swelling due to fluid accumulation.
What are the characteristics of a lymph vessel?
Like veins, lymph vessels contain valves and have thin walls composed of smooth muscle and connective tissue. However, lymph vessels are more flexible to accommodate excess fluid.
Lymph vessels vary in size, like those of the circulatory system. Smaller lymph capillaries give rise to larger vessels.
What are the characteristics of a lymph node?
Lymph nodes are small structures, oval in shape, and positioned along lymph vessels. They contain immune cells, namely lymphocytes and macrophages.
Lymph nodes function to filter the fluid that is being transported through the lymphatic system.