Exam 4: Body Defense 3rd

Question 1

In what ways does the third line of defense differ from innate immunity?

Answer 1

Innate immunity is a broad spectrum response. While the third line of defense is adaptive immunity, specific responses and targets.

Question 2

Adaptive immunity

Answer 2

also called acquired immunity. Activated by specific pathogens, differs between individuals (based upon the pathogens they have previously encountered), slower than innate response.

Question 3

What are the five key attributes of adaptive immunity? Briefly describe all five of them.

Answer 3

1) Specificity- acts against only one particular pathogen, more specifically one particular molecular shape. This molecule is termed antigen (antibody-generating).

2) Inducibility- cells involved in adaptive immunity are activated by the specific antigen-containing pathogen.

3) Clonality- induced cells expand into large numbers of identical cells termed colones.

4) Unresponsiveness to self- adaptive immunity acts against foreign molecules and not against normal molecules or cells of the body.
Adaptive responses are self-tolerant.

5) Memory- immunological memory. The immune system adapts to respond faster and more effectively in subsequent encounters with a particular pathogen.

Question 4

What are the two types of lymphocytes? Why are they named in this manner?

Answer 4

lymphocytes are a type of leukocyte (WBC). B lymphocytes and T lymphocytes. Named based on where they mature. B arises/matures in bone marrow while T begins in bone marrow but travel and mature in thymus.

Question 5

What types of proteins are super-abundant on the surface of B and T cells? Roughly how many copies of this protein are present in each cell? How similar are these proteins to each other upon a single cell? How similar are these proteins to each other when we compare two different cells?

Answer 5

Antigen receptors. ~100,000 identical copies of these receptors per lymphocyte. All receptors made by one cell are identical. The proteins are going to be different cell to cell.

Question 6

How can we produce literally millions of distinctly different antigen receptor proteins when humans possess only about 22,000 genes?

Answer 6

Genes for receptors (and for antibodies) are assembled in multiple variations through “DNA splicing”. Produces great variation in the shapes of the antigen-binding sites.

Question 7

Where in the human body do large concentrations of lymphocytes tend to lie in wait for pathogens?

Answer 7

After B and T develop they move via the blood to various parts of the lymphatic system. Lymph nodes, spleens, etc. Take up residence in these locations. Encounter and destroy pathogens in these locations.

Question 8

Cell-mediated immune response

Answer 8

Controlled and carried out by T cells. Often act against intracellular pathogens e.g viruses inside cells.

Question 9

Antibody responses

Answer 9

aka humoral immune response. Controlled and carried out by the B cells, B cells produce antibodies that recognize & bind to specific antigens. T cells also play a role. Often act against extracellular pathogens.

Question 10

Do cell-mediated immune responses or antibody responses act against extracellular pathogens?

Answer 10

Cell-mediated immune response= intracellular pathogens

Antibody responses=extracellular pathogens.

Question 11

Compare and contrast cell-mediated immune responses and antibody responses.

Answer 11

Both stimulate & regulate innate defenses (defenses 1 and 2). Both act directly against the pathogen. Cell mediated only involves T cells while antibody involves both B and T. Both could aberrantly attach a body’s cells although they should not.

Question 12

Immunological memory

Answer 12

The ability of the immune system to respond more rapidly and effectively to pathogens that have been encountered previously

Question 13

In what way do antibodies resemble antigen receptors?

Answer 13

Antigen receptors and antibodies bind specifically to antigens they recognize. Pathogens with these antigens are identified and destroyed.

Question 14

What is an antigen? How does it relate to an epitope?

Answer 14

Antigens are the specific portions of cells or specific molecules recognized as foreign. Antibody-generating molecules. Antibodies are generated that specifically recognize these antigens. Lymphocytes and antibodies bind to antigens which trigger immune response.

Epitope is the specific portion of an antigen that antibodies bind to. Also called “antigenic determinants”

Question 15

Can an antigen possess multiple epitopes? Explain.

Answer 15

Yes, each would be specifically recognized by a different antibody.

Question 16

Can an antigen be specifically recognized by more than one distinctly different type of antibody? Explain.

Answer 16

Yes, a single antigen may have multiple different epitopes. Each is specifically recognized by a different antibody. Thus a single antigen can stimulate the immune system to activate several distinct lymphocytes and produce several different antibodies.

Question 17

Can an epitope be specifically recognized by more than one distinctly different type of antibody? Explain.

Answer 17

No, shape recognition is occurring. One antibody matches a distinct epitope.

Question 18

An antibody is roughly shaped like the letter “Y.” Which regions of this antibody specifically bind to an antigen?

Answer 18

Antigen-bnding site on the tip of each arm. The two binding sites on a give antibody are identical. Veriety of shapes possible due to DNA splicing of the genes encoding the polypeptides.

Question 19

How was the term “antigen” derived? Does it stand for something?

Answer 19

Antibody-generating molecules

Question 20

Not all molecules make effective antigens. What characteristics of molecules tend to make them better antigens?

Answer 20

Shape, size, and complexity matter.

Large molecules make better antigens. Especially proteins and glycoproteins. Small molecules make poor antigens by themselves, and can become antigenic when bound to larger molecules. e.g penicillin is normally not antigenic, but when bound to a carrier protein in the blood it can become antigenic and trigger an allergic response in some people.

Complex molecules with distinctive shapes make better antigens. Possess more epitopes to which antibodies could bind. e.g starch is a poor antigen, made of repeating sugar subunits,not very structurally complex. In comparison glycoproteins are effective antigens, they possess multiple distinctive shapes and novel combinations of subunits that the immune system can recognize as foreign.

Question 21

Examples of effective antigens?

Answer 21

Components bacteria cell walls, capsules, pili, flagella. External and internal proteins of viruses, fungi, and protozoa. Some toxins.

Question 22

Exogenous antigens

Answer 22

Come from outside the body’s cells. Structural components of microbes and secreted products.

Question 23

Endogenous antigens

Answer 23

Produced within the cells of the body infected by pathogens. The immune system can respond to these antigens if they are displayed on the surface of the cell.

Question 24

Autoantigens

Answer 24

• Molecules derived from normal cellular processes.
• Normally not antigenic because immune cells that would respond to them are removed during the formation of the immune system (“clonal deletion” provides “self-tolerance”).

Question 25

What are the three categories of antigens?

Answer 25

Exogenous antigens
Endogenous antigens
Autoantigens

Question 26

Colonel deletion

Answer 26

In immunology, clonal deletion is the removal through apoptosis of B cells and T cells that have expressed receptors for self before developing into fully immunocompetent lymphocytes. This prevents recognition and destruction of self host cells, making it a type of negative selection or central tolerance.

Question 27

What is the purpose of clonal selection?

Answer 27

Antigenic-specific selection of a lymphocyte that activates it to produce clones of effector cells dedicated to eliminating the antigen that provoked the initial immune response.

Question 28

Briefly describe the process of clonal selection.

Answer 28

An antigen encounters a diverse pool of lymphocytes. A given antigen interacts with only a few lymphocytes. Activation by an antigen stimulates the proliferation (replication) of theses specific lymphocytes. A “clone” of identical cells is formed following this “selection” by a specific antigen. Majority of the produced cells are effector cells and a few are e B cells are memory cells

Question 29

Assuming you have never been infected by the ebola virus, does your body possess any cells with antigen receptors that specifically recognize antigens specific to the ebola virus? How many such cells do you possess? If you had been infected by ebola and had recovered, would your answer be any different? Explain.

Answer 29

Yes, the body has B cells that can recognize ebola antigens even though never been infected. However the number of B cells that recognize ebola is greater than zero but not very many, will stay this way as long as the body does not encounter ebola. If infected and recovered form ebola the body will have a significant amount of theses antigen receptors.

Question 30

During the process of clonal selection, what two types of cells are produced? Are both immediately available to combat the infection? Explain.

Answer 30

Effector cells act immediately to compact the infection. Memory cells, not active immediately but can activate the immune system upon subsequent exposure to the antigen.

Question 31

What is a primary immune response?

Answer 31

Occurs when an antigen is encountered for the first time. Only a few lymphocytes are activated, there aren’t many lymphocytes that recognize this antigen.

Question 32

Describe the occurrences during a primary immune response. How fast is this response? When does antibody production generally peak during this process?

Answer 32

Fairly slow, antibody production typically peaks in 2-3 weeks.

Question 33

What is a secondary immune response?

Answer 33

Occurs when antigen is encountered subsequently. Large pool of memory cells is activated, they produce both effector cells and memory cells.

Question 34

Describe the occurrences during a secondary immune response. How fast is this response? When does antibody production generally peak during this process? When do antibodies tend to reach levels equivalent to their maximal level in a primary immune response?

Answer 34

Faster and stronger than the primary response. May take two weeks to peak, but reaches levels equivalent to primary response peak in under a week.

Question 35

How are memory cells related to the primary immune response?

Answer 35

Very few at the start of response but memory cells are produced so they can be useful next time.

Question 36

How are memory cells related to the secondary immune response?

Answer 36

Many present at the start and act to trigger the secondary immune response.

Question 37

Briefly describe the structure of an antibody.

Answer 37

Consists of 4 polypeptides of two different types bound together into a Y shape. There is an antigen-binding site on the tip of each arm, 2 total. The two binding site on a given antibody are identical. Great variety in the shape of these sites due to DNA splicing of the genes encoding theses polypeptides. Stem helps mediate the disposal of the bound antigen.

Question 38

Where are the antigen-binding sites of an antibody?

Answer 38

At the tip of each arm of the Y shape.

Question 39

Describe at least two ways in which antibody-antigen binding leads to destruction of the antigen-possessing pathogen.

Answer 39

Recognition of an antigen by an antibody ultimately results in the destruction of the antigen. Multiple methods including phagocytosis and cell lysis.

Question 40

What is an antigen-presenting cell?

Answer 40

Macrophages and other phagocytic cells ingest microbes and foreign particles. Foreign molecules are broken down and fragments (antigens) are pressed on the surface of the cell.

Question 41

How do helper T cells interact with antigen-presenting cells?

Answer 41

Helper T cells recognize antigen-presenting cells with complementary cell-surface receptors.

Question 42

What events follow the stimulation of a helper T cell by an antigen-presenting cell?

Answer 42

Signaling molecules from the APC assist activation of colonel selection of helper T cells. Activated helper T cells stimulate other cells, B cells and cytotoxic T cells.

Question 43

How do cytotoxic T cells interact with virally infected cells?

Answer 43

Infected cells present foreign antigens on their surface. Cytotoxic T cells with complementary receptors bind to these presented antigens. The cytotoxic T cells secrete the protein perfin and releases hydrolytic enzyme, Perforin attaches t the infected cell and punches holes in the membrane. Enzyme enter infected cells by endocytosis and break down proteins.

Question 44

How do cytotoxic T cells destroy virally infected cells?

Answer 44

Cytotoxic T cells secrete the protein perforin and releases hydrolytic enzymes.

• Perforin attaches to the infected cell and punches holes in its membrane

• Enzymes enter infected cell by
endocytosis and break down proteins

Question 45

Describe the Immune response process.

Answer 45

Microbe interacts with lymphocyte via antigen receptors. Lymphocyte replication is triggered creating effector and memory cells. Effector cells secrete antibodies, Y shaped antibodies bind to the antigens tagging them for destruction. Macrophages and other phagocytic cells ingest the tagged microbes.