Exam 2

Question 1

A high affinity antibody associated with long-term immunity:

Answer 1

IgG

Question 2

Low affinity antibody with ten antigen binding sites:

Answer 2

IgM

Question 3

The main type of antibody found in gastrointestinal mucus secretions:

Answer 3

IgA

Question 4

If a cell surface molecule is labeled as Fc mew R, this tells you that it
a. binds to the Fc end of any antibody molecule
b. is an IgM receptor
c. serves as a paratope for the Fc epitope
d. has affinity for the Fab region of antibodies

Answer 4

b. is an IgM receptor

Question 5

What is the role of the proteasome?
a. It is used by phagocytes to kill bacteria inside a phagolysosome
b. it is the molecule that binds to a TCR
c. it is used by infected cells to degrade antigens in the cytoplasm
d. it is the molecule used by cytotoxic T cells to recognize infected cells

Answer 5

c. it is used by infected cells to degrade antigen in the cytoplasm

Question 6

Which of the following does not apply to T cell receptors?
a. secreted
b. 2 chains
c. antigen specific
d. MHC restricted

Answer 6

a. secreted

Question 7

An Ig isotype switch from IgM to IgG involves
a. RNA splicing
b. hypermutations
c. VDJ recombinations
d. DNA deletion
e. all of the above

Answer 7

d. DNA deletion

Question 8

MHC Class II molecules are found on
a. CD4 T cells
b. macrophages
c. infected cells
d. CD8 T cells
e. none of the above

Answer 8

b. macrophages

Question 9

To prevent grafted tissues to be rejected, donors and recipients must be matched for
a. VJ genes
b. VDJ genes
c. red blood cell types
d. specific HLA genes
e. all of the above

Answer 9

d. specific HLA genes

Question 10

The CD8 molecule
a. is a co-receptor
b. is a molecule that protects the TCR
c. is a type of T cell receptor
d. presents antigens to cytotoxic T cells

Answer 10

a. is a co-receptor

Question 11

Affinity maturation of B cells takes place in
a. the bone marrow
b. germinal centers
c. the bloodstream
d. the T cell area of lymph nodes

Answer 11

b. germinal centers

Question 12

Negative selection of B cells takes place in the
a. germinal centers
b. spleen
c. thymus
d. bone marrow

Answer 12

d. bone marrow

Question 13

Which of the following is associated with allergies?
a. IgD
b. IgM
c. IgE
d. IgG

Answer 13

c. IgE

Question 14

Which of the following cells can be activated (induced) by a CD4 T cell?
a. b cells
b. mast cells
c. red blood cells
d. plasma cells

Answer 14

a. B cells

Question 15

Define Affinity

Answer 15

The strength of the interaction between the antigen-binding site (paratope) on an antibody and the epitope on an antigen

Question 16

Define Avidity

Answer 16

The overall strength of binding between an antibody and a multivalent antigen, considering all binding sites

Question 17

Define Epitope

Answer 17

the specific part of an antigen that is recognized and bound by an antibody or a T cell receptor

Question 18

Define paratope

Answer 18

the specific region on an antibody or T cell receptor that binds to an epitope on an antigen

Question 19

Define tolerance

Answer 19

the immune system’s ability to recognize and avoid attacking the body’s own cells and tissues

Question 20

Define MHC restriction

Answer 20

The requirement that T cells recognize antigens only when they are presented on host cells by Major Histocompatibility Complex (MHC) molecules. CD8 T cells are restricted to MHC class I, while CD4 T cells are restricted to MHC class II molecules

Question 21

Differentiate between MHC I and MHC II molecules. What are their respective roles in immunity? On what cells are they found and what do they do?

Answer 21

> MHC I: Found on All nucleated cells, presents intracellular antigens, recognized by CD8+ T cells, function is to activate cytotoxic T cells to destroy infected or abnormal cells

> MHC II: Found on APCs (dendritic cells, macrophages, B cells), presents extracellular antigens, recognized by CD4+ T cells, function is to activate helper T cells to coordinate immune responses

Question 22

What happens to B cells that bind to self-antigens on bone marrow stromal cells?

Answer 22

They undergo negative selection
> Receptor editing: The B cell modifies its B cell receptor (BCR) to create a new, non-self-reactive receptor
> apoptosis: the self-reactive B cells is eliminated through programmed cell death

Question 23

What are the differences in the type of antigens recognized by antibodies and T cell receptors?

Answer 23

> Antibodies: recognize intact, extracellular antigens. Can be proteins, polysaccharides, lipids, or nucleic acids, and antibodies bind directly to the surface of these antigens in their native form
T cell receptors: recognize process antigens that are presented as small peptide fragments bound to MHC molecules. These antigens must be presented by an antigen-presenting cell (APC) on MHC class I or II molecules

Question 24

In response to a given antigen, B cells differentiate; some cells secrete IgM whereas other cells secrete IgG. How is this possible? How can two different Ig molecules be produced against the same antigen?

Answer 24

> It is possible because B cells can go through a process called class switch recombination (CSR) which allows them to make antibodies of a different isotype.
B cells start producing IgM when exposed to an antigen.
As the immune response progresses, B cells receive additional signals from helper T cells and cytokines, and undergo CSR. This happens in the constant region of Ig gene (not the variable region).
B cell now produces IgG antibodies while maintaining the same antigen specificity. The signals that induce CSR are usually provided by T cells through cytokines like IL-4 or IFN-gamma
allows them to use antibodies with the different effector functions for same pathogen

Question 25

What are the differences (and possible similarities) between DNA recombination of gene segments and RNA splicing of exons? How does this relate to our understanding of the immune response as it applies to B cells and immunoglobulins?

Answer 25

Differences: >DNA recombo happens at DNA level in B cells during their development. It rearranges VDJ gene segments to create diverse Ag-binding regions in Ab (permanent DNA change) >RNA splicing occurs after transcription at the RNA level in all cells. It removes introns and joins exons to produce mature mRNA. In B cells it helps determine whether an Ab is membrane-bound or secreted, or which isotype is expressed. Similarities: >Both processes create diversity, DNA recombo creates Ag binding variety, while RNA splicing allows diff forms of the same Ab >Both involve precise cutting and joining of genetic material Ig relevance: >DNA recombo generates diverse Ag specificities >RNA splicing controls Ab form and isotype, influcing B cell response to Ag

Question 26

What mechanisms are responsible for generating antibody diversity?

Answer 26

V(D)J Recombo: >During B cell development VDJ are randomly recombined >heavy chains (VDJ), light chains (VJ), produces unique variable regions, determining Ag specificity of the Ab Junctional Diversity: >During VDJ recombo, nucleotides are randomly added or removed at the junction between V,D, and J segments by enzymes such as TdT >Increases diversity by altering the sequence of the Ag binding region Somatic Hypermutation: >After B cell encounters an Ag, the variable region of the Ab gene undergoes SH in the germinal centers >This introduces point mutations at a high rate in the DNA coding for the VR, resulting in slight changes in the Ab's affinity for its Ag Class Switch Recombo: >B cells switch Ig produced by changing the constant region, no change in variable >enables different effector functions without changing antigen specificity