Antigen Processing & Presentation: Clonal Selection & T-cell Response (Satti)

Question 1

What type of antigens are presented by MHC class I molecules?

Answer 1

Endogenous antigens

Endogenous antigens originate from inside the cell.

Question 2

What is the role of cytolytic T-cells when activated by MHC class I?

Answer 2

Destroy host cells displaying foreign antigens

Cytolytic T-cells are activated by the presence of foreign antigens on MHC I.

Question 3

How can exogenous antigens be presented on MHC class I?

Answer 3

Through cross-presentation

Exogenous peptide antigens escape the late endosome and enter the endogenous processing pathway.

Question 4

What type of antigens are presented by MHC class II molecules?

Answer 4

Exogenous antigens

Exogenous antigens originate from outside the cell.

Question 5

What are antigen presenting cells (APC) responsible for?

Answer 5

Presenting exogenous antigens using MHC class II molecules. They can also utilize MCH class I.

APCs produce MHC II molecules to present antigens.

Question 6

What happens when exogenous antigens bind to MHC class II?

Answer 6

They are transported to the APC surface for presentation

Antigens bind in late endosomes and are then presented on the cell surface.

Question 7

What is the result of a host cell presenting foreign antigen on MHC I?

Answer 7

Activation of CD8+ T-cells leading to host cell destruction

This is part of the cell-mediated immune response.

Question 8

What is the role of CD4+ T-cells activated by MHC class II?

Answer 8

Secrete cytokines to aid B-cell maturation and cytolytic T-cell clones

CD4+ T-cells act as helpers in the immune response.

Question 9

Why is antigen processing necessary for T-cell activation?

Answer 9

T-cells can only detect short peptide fragments bound to MHC molecules

Unprocessed antigens cannot be recognized by T-cells.

Question 10

What is the source of endogenous antigens?

Answer 10

Proteins generated within the cell

Examples include viral proteins or abnormal proteins in cancer cells.

Question 11

How are endogenous antigens processed?

Answer 11

Degraded by proteasome in cytoplasm and transported into the ER

This process prepares peptides for MHC I loading.

Question 12

What MHC molecule is involved in presenting endogenous antigens?

Answer 12

MHC class I

MHC class I presents peptides derived from endogenous sources.

Question 13

What is the target cell type for MHC class I presented antigens?

Answer 13

CD8+ cytotoxic T cells

These T-cells are responsible for killing infected or abnormal host cells.

Question 14

What happens to host cells presenting foreign antigen on MHC II?

Answer 14

CD4+ T-cells activate and help in the humoral response

This includes aiding B-cells and activating cytotoxic T-cells.

Question 15

Fill in the blank: Antigen processing allows for foreign proteins to be broken down into a form that ______ can recognize.

Answer 15

T-cells

T cells require processed peptide fragments for recognition.

Question 16

True or False: MHC molecules can bind unprocessed or broken down antigens.

Answer 16

False

MHC molecules only bind linear peptide antigens.

Question 17

What is the processing method for exogenous antigens?

Answer 17

Internalized by APCs through phagocytosis or endocytosis

Exogenous antigens are processed within endosomes/lysosomes.

Question 18

What MHC molecule presents exogenous antigens?

Answer 18

MHC class II

MHC class II is responsible for presenting exogenous peptides.

Question 19

What is the role of B cells in the immune response activated by MHC class II?

Answer 19

Produce antibodies to help destroy pathogens

B cells are part of the humoral immune response.

Question 20

MHC molecules bind only __________ antigens and activate only ________ (they cannot bind unprocessed or broken down antigens).

Answer 20

MHC molecules bind only linear peptide antigens and activate only T-cells (they cannot bind unprocessed or broken down antigens).