Question 1

Why are HLA heterozygotes more resistant to disease than homozygotes?&#10;A) They have more single nucleotide polymorphisms.&#10;B) They have a more diverse range of minor HLA loci.&#10;C) They have more diversity in the antibodies they produce.&#10;D) They have a more varied repertoire of antigen-presenting HLA molecules.

Accepted Answer

Heterozygotes are more resistant to infection because they have inherited a larger repertoire of antigen-presenting molecules. The diversity occurs because the haplotypes are inherited as a block from each parent and are co-dominant, so if they inherit two different haplotypes they will express a greater variety of HLA molecules. Also, recombination can occur between the haplotypes, leading to greater diversity. The HLA genes are not related to antibody diversity. Heterozygosity would not lead directly to more single nucleotide polymorphisms. Heterozygotes may have a more diverse array of minor HLA antigens, but these will not have as much of an effect on resistance to disease and the functions are limited or unknown at this time.

Question 2

HLA class III genes produce:&#10;A) Stress molecules&#10;B) Complement components&#10;C) Antigen presenting molecules&#10;D) Receptors that activate natural killer (NK) cells

Accepted Answer

HLA class III genes do not produce the antigen presenting molecules that classes I and II produce. Instead, HLA class III genes produce some complement proteins and tumor necrosis factor (TNF). They also do not produce stress molecules or receptors related to NK cells.

Question 3

CD1 molecules are similar in structure to:
I- HLA class I molecules
III- HLA class II molecules
III- HLA class III molecules

A) I only
B) III only
C) I and II
D) II and III
E) I, II, and III

I only

Accepted Answer

CD1 molecules have a similar structure to HLA class I molecules, with both possessing an a-chain attached to b₂-microglobulin.

Question 4

HLA class II molecule consists of:&#10;A) Three glycosylated a-chains&#10;B) Heavily glycosylated a- and b-chain&#10;C) Two glycosylated a-chains and three b-chains&#10;D) A single glycosylated a-chain bound to b2-microglobulin

Accepted Answer

HLA class II molecules consist of two heavily glycosylated chains, one a-chain and one b-chain. HLA class I molecules consist of a single glycosylated a-chain attached to b₂-microglobulin.

Question 5

Human leukocyte antigen (HLA) class I molecules bind antigens:&#10;A) At the ends and the antigens are larger than HLA class II antigens&#10;B) At the ends and the antigens are smaller than HLA class II antigens&#10;C) In the middle and the antigens are larger than HLA class II antigens&#10;D) In the middle and the antigens are smaller than HLA class II antigens

Accepted Answer

HLA class I molecules bind short amino acid sequences (8-12 a.a.) at the ends, while HLA class II molecules bind longer antigens (10-30 a.a.) in the middle of the sequence. Because they bind at the ends of the antigen, HLA class I molecules can only bind short peptides because the binding groove is smaller.

Question 6

In bare lymphocyte syndrome, individuals lack which surface molecules on their lymphocytes?&#10;A) CD4&#10;B) CD8&#10;C) HLA class I molecules&#10;D) HLA class II molecules

Accepted Answer

Individuals who have bare lymphocyte syndrome have an immunodeficiency in which the B cells and monocytes do not express HLA class II molecules. Therefore, those cells cannot present antigen, and the individual is at high risk for infection.

Question 7

Allelic polymorphism assures that some members of a species will survive a microbial infection because the different alleles:&#10;A) Better distinguish between foreign and self&#10;B) Provide receptors with greater affinity for antigen&#10;C) Allow the immune system to respond to a wide range of antigens&#10;D) Produce a greater variety of cytokines to assist in the immune response

Accepted Answer

The different alleles provide a diverse response to infection, and ensure that some members of a species will survive even if a microbe displays a host self antigen, because the diversity of the HLA genes will still allow for an appropriate immune response to other antigens.

Question 8

A set of HLA antigens on the same chromosome is called a:&#10;A) Gene&#10;B) Hapten&#10;C) Haplotype&#10;D) Single nucleotide polymorphism (SNP)

Accepted Answer

A set of HLA antigens on the same chromosome is known as a haplotype. The haplotype is made up of a group of genes. These are not related to haptens, and SNPs may or may not occur throughout these genes.

Question 9

Which of the following molecules are capable of presenting antigen?
I. CD1 molecules
II. HLA class I molecules
III. HLA class II molecules

A) I only
B) III only
C) I and II
D) II and III
E) I, II, and III

Accepted Answer

All three types of molecules can present antigen. HLA class I present antigen to CD8 T cells, and HLA class II molecules present antigen to CD4 T cells. CD1 molecules are antigen presenting molecules outside the HLA complex and present highly conserved glycolipids to CD4 T cells.

Question 10

Individuals who express HLA-DR13:&#10;A) Can more easily clear hepatitis B virus&#10;B) Are more susceptible to tuberculosis infection&#10;C) Are more susceptible to Candida albicans infections&#10;D) Can more easily eliminate respiratory syncytial virus (RSV)

Accepted Answer

Homozygous expression of the HLA-DR13 gene provides the individual with more efficient presentation of hepatitis B antigens, a vigorous CD4 response, and accelerated viral clearance. This increased response to the hepatitis B virus protects the individual from developing chronic hepatitis.

Deck 4: Antigen Presenting Molecules