Question

APCs break ___________ apart in lysosomes, creating pieces which can be displayed in the groove of a major histocompatibility complex (MHC) on the surface of the APC.

1. Antigens
2. Enzymes
3. Proteins
4. Nucleic acids

Answer 1

APCs break antigens apart in lysosomes, creating fragments that are displayed on MHC molecules for T-cell recognition, initiating an adaptive immune response.

Step-by-step explanation:

The question asks which substances Antigen-Presenting Cells (APCs) break apart in lysosomes for display on Major Histocompatibility Complex (MHC) molecules. The correct answer is that APCs break antigens apart in lysosomes, resulting in pieces that can be displayed in the groove of an MHC molecule on the surface of the APC. In the context of immune response, after the APC, such as a macrophage or dendritic cell, has engulfed an antigen through phagocytosis, the resultant phagocytic vesicle merges with a lysosome to form a phagolysosome. Here, enzymes degrade the antigen into fragments. These fragments, or epitopes, are then selected for their immunogenicity, loaded onto MHC class I or class II molecules according to the intracellular or extracellular origin of the antigen, and presented on the cell surface for T-cell recognition, thus initiating an adaptive immune response.