Antigen processing and presentation

Question 1

what is antigen processing and presentation

Answer 1

It is the process by which antigen-presenting cells digest antigens acquired from inside or outside the cell and display the resulting antigenic fragments on cells surface MHC molecules for recognition by T lymphocytes

Question 2

what cells are involved in the process of antigen processing and presentation

Answer 2

• Antigen-presenting cells (APC)
  
  • they digestion (processing) and display (presentation)
• Later, T lymphocytes recognize the presented antigens and get activated to initiate a cellular immune response

Question 3

What are the 3 professional antigen-presenting cells

Answer 3

1. Dendritic cells
2. Macrophages
3. B lymphocytes

Question 4

what is the function of Dendritic cells as professional antigen-presenting cells

Answer 4

Present antigen to naive CD4+ and CD8+ T lymphocytes, so they initiate T-cell responses

Question 5

what is the function of Macrophages cells as professional antigen-presenting cells

Answer 5

present antigens to differentiated CD4+ T lymphocytes in the effector phase of cell-mediated immunity

Question 6

what is the function of B lymphocytes cells as professional antigen-presenting cells

Answer 6

present antigens to helper T cells (CD4+) during humoral immune response

Question 7

what other cells can act as non-professional antigen presenting cells

Answer 7

all other nucleated cells when they become infected, particularly with virus

Question 8

how is MHC-2 expression on macrophage

Answer 8

Low levels: introduced by PAMPs, DAMPs, and cytokines

Question 9

how is MHC-2 expression on DC

Answer 9

always expressed

Question 10

how is MHC-2 expression on B cell

Answer 10

always expressed, inducible on activation

Question 11

how are antigen types and presentation by MHC with macrophages

Answer 11

Extracellular antigens: presentation via MHC 2

Question 12

how are antigen types and presentation by MHC with DC

Answer 12

Intracellular and extracellular antigens: presentation via MHC 1 and MHC 2

Question 13

how are antigen types and presentation by MHC with B cell

Answer 13

Extracellular antigen binds to specific Ig receptors: presentation via MHC 2

Question 14

Location of macrophages

Answer 14

Lymphoid tissue connective tissue body cavities

Question 15

Location of DC

Answer 15

Lymphoid tissue connective tissue Epithelium

Question 16

Location of B cells

Answer 16

lymphoid tissue Blood

Question 17

the responses of antigen specific T-cells to proteins requires the participation of ________________, which capture, digest and display the antigens to T-cells

Answer 17

the responses of antigen specific T-cells to proteins requires the participation of Antigen Presenting cells (APCs), which capture, digest and display the antigens to T-cells

Question 18

Two important functions of antigen presenting cells

Answer 18

1. they convert protein antigens to peptides and they display peptide MHC complexes for recognition by T-cells
   
   1. conversion of proteins to peptides within APCs is called antigen processing
2. APCs provide stimulus to T-cells, the stimulus is called co-stimulation

Question 19

what does antigen presentation begin with

Answer 19

antigen presentation begins with antigen processing

Question 20

the pathway of antigen processing convert protein antigens derived from the ___________ or the ____________ and load these peptides into MHC molecules for display to lymphocytes

Answer 20

the pathway of antigen processing convert protein antigens derived from the extracellular space or the cytosol into peptides and load these peptides into MHC molecules for display to lymphocytes

Question 21

Protein antigens present in acidic vesicular compartments of APCs generate_________ whereas antigens present in the cytosol generate___________

Answer 21

Protein antigens present in acidic vesicular compartments of APCs generate MHC class 2 associated peptides whereas antigens present in the cytosol generate MHC class I-associated peptides

Question 22

what is the sequence of events for processing of endocytosed antigens for MHC class 2-associated presentation: sequence of events

Answer 22

1. uptake: of extracellular proteins into vesicular compartments of APCs
2. Processing: of internalized proteins in endosomal and lysosomal vesicles
3. Biosynthesis and Transportation of MHC class 2 molecules: to endosomes
4. Association: of processed peptides with MHC class 2 molecules in vesicles
5. Expression: of peptide-class 2 complexes on the APC surface

Question 23

what happens to the material once internalized

Answer 23

the uptaken material is localized in vesicles called endosomes

Question 24

what are endosomes

Answer 24

endosomes are acidic compartments that contain proteolytic enzymes

Question 25

what happens when the endosomes communicate with lysosomes

Answer 25

form phagolysosomes or secondary lysosomes, where further degradation of engulfed material takes place

Question 26

Internalized proteins are degraded _________ in _________ and lysosomes

Answer 26

Internalized proteins are degraded enzymatically in Late endosomes and lysosomes

Question 27

what is created when the proteins are degraded

Answer 27

about 14-20aa long peptides are generated that bind to the peptide-binding clefts of class 2 MHC molecules

Question 28

what are the most important proteolytic enzymes involved in protein degradation

Answer 28

Cathepsins

Question 29

how are the MHC 2 bio synnthesised and transport

Answer 29

• The alpha and beta chains of the MHC class 2 molecule are synthesized and associated with each other in the endoplasmic reticulum (ER)
• Upon synthesis in the ER, MHC class 2 molecules are transported to the Golgi apparatus and to endosomes with an associated invariant chain (I)
• In endosomes, the I dissociates and the antigenic peptides are associated with MHC class 2 molecules
• Stable peptide-MHC class 2 complexes are delivered to the surface of the APC, where they are displayed for recognition by CD4+ T lymphocytes

Question 30

what are the sequence of events for processing of cytosolic antigens for MHC class 1 associated presentation

Answer 30

1. Cytosol location of foreign proteins
2. Proteolytic degradation of cytosolic proteins in the proteosome
3. Transport of peptides from the cytosol to the ER
4. Assembly of peptide MHC class 1 complexes in the ER
5. Surface express of peptides MHC class 1 complexes

Question 31

Sources of cytosolic antigens

Answer 31

• Proteins that are found in the cytosol are endogenously synthesized in nucleated cells
• Cytosolic proteins may originate from viruses or other intracellular microbes that infect cells
• Sometimes even endocytosed antigens may be presented through MHC class 1 molecules

Question 32

what happens to the proteins that are synthesized in the cytosol

Answer 32

proteins synthesized in the cytosol are ubiquitinated thus destined for proteosomal degradation

Question 33

what are proteosomes

Answer 33

large multienzyme complex found in the cytoplasm of most cells and has a broad range of proteolytic activity

Question 34

how are peptides derived from cytosolic protein antigens

Answer 34

by proteolysis in the proteosome

Question 35

How are the peptides generated in the proteosome transported to the ER

Answer 35

The main transporting system is the “transporter associated with antigen presentation (TAP)

Question 36

where is TAP located

Answer 36

in the membrane of the ER

Question 37

what is the function of TAP

Answer 37

it mediates the transport of peptides into the ER

Question 38

what happens to the proteins in the assembly of peptide MHC class 1 complexes in the ER

Answer 38

Peptides translocated into the ER bind MHC class 1 molecules that are attached to the TAP dimer

Question 39

how are the MHC class 1 peptide complex surface expressed

Answer 39

• MHC class 1 peptide complexes move through the Golgi complex and are delivered to the cell surface
• MHC class 1 molecules with bound peptides are structurally stable and are expressed on the cell surface
• once expressed on the cell surface, complexes may be recognized by peptide antigen-s[ecific CD8+ t lymphocytes