MHC & APC

Question 1

Locations of Antigen Presentation

Answer 1

1. Primary Lymphoid Tissues: Bone Marrow & Thymus

2. Secondary Lymphoid tissues: Lymph Nodes, Spleen, MALT/other ALTs

Question 2

Conventional Dendritic Cells

Answer 2

1. Location: Tissues
2. TLRs Expressed: TLR 4, 5, 8
3. Cytokines Produced: TNF, IL-6, 12
4. Major Functions: APC to T cells for most antigens

Question 3

Plasmacytoid Dendritic Cells

Answer 3

1. Location: Blood & Tissues
2. TLRs Expressed: TLR 7, 9
3. Cytokines Produced: Type I IFN
4. Major Functions: APC to T Cells for viral infections

Question 4

Stages of Dendritic Cell Maturation

Answer 4

1. Immature dendritic Cells in epithelium recognize microbial antigens through TLRs.
2. Activated TLRs signal cytokines to promote dendritic cell maturation.
3. Chemokines produced in the lymph nodes promote migration of dendritic cells to lymph nodes.
4. Mature dendritic cells can present PROTEIN antigens to naive T cells in lymph nodes.

Question 5

Antigen Recognition of B Cell

Answer 5

• B Cells can DIRECTLY bind to any type (protein, lipids, polysaccharides, etc.) of antigens without MHC molecules.
• B cell binds to antigens using cell-surface immunoglobulins (antibody)
• Mature B cells (Plasma Cells) produce antibody that can either neutralize microbe or opsonize for destruction.

Question 6

Antigen Recognition of T Cell

Answer 6

• T cells ONLY bind to short PEPTIDE antigens that are bound to MHC molecule.
• T cells bind to BOTH the foreign peptide antigen and the MHC molecule.

Question 7

Describe MHC I

Answer 7

• MHC I is found on ALL nucleated cells in the body. It displays peptide antigens that are found within the cytoplasm of cells (“endogenous”).
• MHC I + peptide antigen is recognized by CD8+ T Cell.

Question 8

Describe MHC II

Answer 8

• MHC II is only found on professional APC such as macrophages, dendritic cells, and B Cells. It displays peptide antigens that are in the APC’s vesicles.
• MHC II + peptide antigen is recognized by CD4+ T Cell.

Question 9

What is HLA?

Answer 9

Human Leukocyte Antigen

• Human MHC gene product
• Found on chromosome #6

Question 10

Human MHC Class I

Answer 10

1. Names: HLA-A, HLA-B, HLA-C
2. Tissue Distribution: all nucleated cells
3. Biological Activity: Present “endogenous” Peptides
4. Structural Features: 2 chains
   - a-chain is transmembrane and binds to the peptide
   - B2m chain just for stability

• Recognized by CD8+ T cell

Question 11

What is TAP and its function?

Answer 11

Transporter-associated Antigen Processing

• The TAP protein binds peptide antigen to MHC I molecule in the ER before they are transported out of the cell to be presented on the cell surface.

Question 12

Human MHC Class II

Answer 12

1. Names: HLA-DP, HLA-DQ, HLA-DR
2. Tissue Distribution: Professional APC’s
3. Biological Activity: Present engulfed “exogenous” Peptides
4. Structural Features: 2 chains (a & B)
   - both chains are transmembrane
   - both chains bind to the peptide
   - Has an Invariant Chain (Ii) attached that gets released when peptide binds.

• Recognized by CD4+ T cell

Question 13

Celiac Disease

Answer 13

Associated with HLA DQ2 and HLA DQ8 genes in Human MHC Class II.

Question 14

Type 1 Diabetes

Answer 14

Associated with HLA DQ and HLA DR genes in Human MHC Class II.

Question 15

Hyperacute Rejection

Answer 15

Immediate rejection of solid organ transplant due to pre-formed antibodies against completely unmatched antigens.

Question 16

Acute Rejection

Answer 16

Due to developing humoral and cell-mediated response to foreign organ.

• treatable with immunosupressant

Question 17

Chronic Rejction

Answer 17

Due to chronic cell-mediated and humoral response to foreign organ.

• May require re-transplant.

Question 18

Graft vs. Host Disease

Answer 18

Occurs in Bone Marrow Transplant

• Due to cell-mediated immunity by donor T Cells against recipient MHCs.
• Cause multiple organ attack