Question

Which of the following is an example of cross-presentation?

A. An endogenous peptide being presented on MHC class I
B. An exogenous peptide being presented on MHC class I
C. An endogenous peptide being presented on MHC class II
D. An exogenous peptide being presented on MHC class II
E. A B-cell antigen being presented to a T cell

Answer 1

The correct answer is B. An exogenous peptide being presented on MHC class I, which is an example of cross-presentation whereby dendritic cells present antigens from phagocytosed pathogens on MHC class I to T cells.

Step-by-step explanation:

The concept of cross-presentation refers to the process where dendritic cells phagocytose a pathogen and present its antigens on MHC class I molecules to T cells, which is unusual as exogenous pathogens are typically presented on MHC class II molecules. Cross-presentation is critical for initiating a cytotoxic T cell response against pathogens that do not infect the presenting cell directly. In the context of the student's question, the correct answer is:

B. An exogenous peptide being presented on MHC class I

This is because cross-presentation specifically involves the presentation of exogenous antigens, which are generally found outside the cells, on MHC class I molecules, normally associated with endogenous antigens found inside the cells.