L06 Antigen Processing and Presentation

Question 1

Extracellular Antigens

Answer 1

B cells (and their products-antibodies) recognize extracellular antigens or those found or exposed on the outside of the cell
- Neutralization
-Active Complement
-Enhance Phagocytosis

Question 2

Not all antigens are __________. Typical virus replication cycle; has both Extracellular and Intracellular Phases

Answer 2

Extracellular

Question 3

Can antibodies gain access to their intracellular environment?

Answer 3

NO
It is a job of the T-lymphocyte system to recognize intracellular antigens

Question 4

Ag processing and recognition

Answer 4

In order for T cells to recognize antigens derived from within a host cell the antigen must be processed

Question 5

Exogenous antigen processing pathway:

Answer 5

• HLA class II molecules are involved
• Activation of CD4+ T helper cells

Question 6

Endogenous antigen processing pathway:

Answer 6

• HLA class I molecules are involved
• Activation of CD8+ cytotoxic T cells

Question 7

The major histocompatibility complex and HLA molecules:

Answer 7

Nearly every vertebrate has an MHC that encodes genes responsible for determination of self and non-self or determination of foreignness
- Human MHC class I and II genes encodes human leukocyte antigens (HLA)- class I and HLA class II, respectively

Question 8

The major histocompatibility complex

Answer 8

Genes for MHC are tightly linked on chromosome 6

Question 9

There are 6 main loci, what are they?

Answer 9

HLA-A, HLA-B and HLA-C for HLA class I

HLA-DP, HLA-DQ and HLA-DR for HLA class II

Question 10

Genetic Polymorphism Exists

Answer 10

Each gene has multiple different stable forms or ‘alleles’

Question 11

Each person possesses two sets of MCH genes

Answer 11

• one on each chromosome 6
• diploid (one chromosome 6 from mom and one chromosome 6 from dad)
  -each consist of both class I and class II loci

Question 12

Inherited “en bloc”

Answer 12

according to Mendelian Genetics
- same six from mom and dad
only 4 different combinations, none are genetically identical to mom and dad
- 1/4 siblings have a perfect genetic match

Question 13

They (HLA class I and II) belong to the ‘ __ _______ family’
(HLA class I and HLA class II molecule)

Answer 13

Ig supergene family

Question 14

What do the HLA class I molecule and HLA class II molecule have in common?

Answer 14

-both have variable amino acid sequence in peptide binding groove
-both have binding sites for co-receptor on T cells
- Both transmembrane glycoproteins which activate signaling molecules

Question 15

HLA Class I molecule (structure, T cell interaction and expression)

Answer 15

Structure - Monomer
beta2 microglobulin
T cell interaction - CD8
Expression - MCH class I (endogenous) - all nucleated cells

Question 16

HLA Class II molecule (structure, T cell interaction and expression)

Answer 16

Structure - dimer
T cell interaction- CD4
Expression - MHC class II (exogenous) APC (antigen presenting cells)

Question 17

MHC I

Answer 17

Endogenous

Question 18

MHC II

Answer 18

Exogenous

Question 19

What type of cell processes exogenous antigens?

Answer 19

If the cell can express HLA class II, it can process and present intracellular Ag to CD4+ T helper cells

Constitutive Expression on:
- Dendritic cells in the spleen & lymph nodes
-Thymic epithelial cells
-B cells

Inducible expression on other cell types such as
- Macrophages
-Fibroblasts
-Endothelial Cells

Question 20

if CLIP bound to MHC II irreversibly, what would happen?

Answer 20

No peptides would be present

Question 21

What type of cells process endogenous Ag?

Answer 21

Essentially all nucleated cells (exception may be neutrophils)
- process can be unregulated