Deck 3: Antigens, Epitopes and Immunogenicity

Question 1

Which is not true of antigenic determinants (or epitopes)?

A) They are restricted portions of a molecule that are involved in the actual binding with the combining site of a particular
Immunoglobulin molecule.
B) The number of distinct antigenic determinants on an antigen molecule varies with its size and chemical complexity.
C) An antigen must have a minimum number of antigenic determinants before it can become immunogenic.
D) A polyclonal antibody response involves the production of different immunoglobulins, each recognizing different epitopes of the same antigen.

Answer 1

Antigens are molecular markers used by the immune system to recognize foreign bodies that have invaded the body. This in turn, results in the generation of an immune response. Hence, it is critical to understand how the antigens perform their function.
The recognition of antigens are by the immune system is due to the presence of molecular motifs known as epitopes, which form part of their structure. These epitopes are involved in the binding of the immunoglobulin to the antigen. The size and complexity of the antigen affects the number and variety of epitopes present on the antigen. Lastly, a polyclonal antibody is specific for more than one epitope on the same antigen.
Hence, options a, b and d are incorrect.
Antigens do not have an epitope threshold , which they need to achieve in order to become immunogenic. As long as the host body is producing immunoglobulin molecules specific for any epitope on the antigen, an immune response is likely to be triggered.
Hence, the correct answer is option .

Question 2

The sharing of 1 or more identical antigenic determinants between 2 different antigens is defined as

A) chemotaxis
B) receptor cross-linking
C) immune complexes
D) immunological cross-reactivity

Answer 2

All of the antigens are not completely unique in their structures. The immunogenecity of antigens is determined by the presence of molecular motifs known as epitopes that are present within the antigen structure. However, sometimes multiple antigens share the same epitope.
Chemotaxis does not refer to the phenomenon of multiple antigens sharing the same epitope. Nor does receptor cross-linking, or immune complexes refer to the phenomenon. These terms are used to refer to very different phenomena involving the immune system.
Hence, options a, b and c are incorrect.
Immunological cross-reactivity refers to the phenomenon of different antigens sharing common determinants. It is also referred as cross-protective immunity or cross-immunity. In humans, hepatitis C virus and influenza virus specific CD8+ (cluster of differentiation) T cell antigens show cross reactivity.
Hence, the correct answer is option .

Question 3

During antigen processing, transportation of antigen peptides to the RER is thought to be mediated by

A) ABC proteins
B) MHC class II molecules
C) MHC class I molecules
D) B-cell receptors

Answer 3

The process by which antigens are captured and processed in the body is a complex. It involves the use of antigen-presenting cells and major histocompatibility complexes (MHC). It helps in gaining a better understanding of these processes.
Class I MHC molecules are responsible for binding to the processed antigen and aiding its recognition by the T cells. The Class II MHC molecules serve a similar function. However, neither of these molecules is responsible for transporting the antigen peptides to the rough endoplasmic reticulum. Likewise, B cell receptors are also not involved in this process.
Hence, options b, c and d are incorrect.
An ABC (ATP binding cassette) protein, TAP (transporter associated with antigen processing) is responsible for the transportation of antigenic peptides to the rough endoplasmic reticulum. Here ATP stands for adenosine triphosphate. This process of transportation occurs by means of vesicle membranes within the cell.
Hence, the correct answer is option .

Question 4

Which is correct about MHC class II molecules?

A) Every nucleated cell expresses them.
B) They are involved in the presentation of endogenous antigens.
C) They are involved in the presentation of antigen peptides to CD8+ T cells.
D) None of the above.

Question 5

During antigen processing, antigen-peptide interaction with MHC class II molecules probably occurs

A) in the nucleus of the antigen-presenting cell
B) at the surface of the antigen-presenting cell
C) in the mitochondria of the antigen-presenting cell
D) in an endosomal or lysosomal compartment

Question 6

In general, which of the following makes the best immunogen?

A) a very large homopolymer
B) a very large protein
C) a polysaccharide
D) a very long nucleic acid

Question 7

A MHC class I molecule

A) can bind most peptides that are 9 amino acids long
B) can bind only whole proteins
C) can bind a specific antigen only, which is determined by an event that occurs during maturation in the absence of antigen
D) can bind a specific antigen only, which is determined by an event that occurs during maturation in the presence of antigen

Question 8

Helper T cells interact with

A) CD4+ molecules
B) CD8+ molecules
C) class I molecules
D) class II molecules

Question 9

Class II molecules

A) must be transported from RER to an endosomal compartment before binding peptides
B) bind to antigen in the RER
C) bind to a blocking protein called ABC protein
D) can only bind peptides smaller than 8 amino acids

Question 10

Which of these is least immunogenic?

A) protein
B) polysaccharides
C) self-proteins
D) all of the above are immunogenic

Question 11

Class II molecules

A) are on every nucleated cell in the body
B) have identical alleles in individuals of the same species
C) are on B cells and macrophages but not on every nucleated cell
D) are on T cells only

Question 12

To be immunogenic, which of the following is not important?

A) charge
B) foreignness
C) chemical complexity
D) molecular weight

Question 13

Which of the following does not act as an adjuvant?

A) Freund's
B) water
C) LPS
D) alum

Question 14

CD4 on T cells binds to

A) CD4
B) MHC class I molecules
C) MHC class II molecules
D) CD8

Question 15

Which of the following is important in the induction of the immune response?

A) amount of antigen
B) timing of the injections
C) route of the injections
D) all of the above are important