The antigen receptor on a T cell recognizes a degraded fragment of a protein (i.e., a peptide) bound to a specialized cell surface peptide-binding receptor called an MHC molecule. One key aspect of this system is that the peptides displayed on MHC molecules can be derived from intracellular proteins. This mode of antigen recognition is particularly important in allowing the adaptive immune response to detect infections by:
A) Large helminthic parasites in the gastrointestinal tract
B) Intracellular pathogens, such as viruses and some protozoa
C) Extracellular bacteria that colonize the lungs
D) Fungi that form hyphae in the bronchial airways
E) Fungal infections in the skin epithelium

Question

Quizplus · Accepted Answer

The ability to recognize peptides derived from intracellular proteins allows T cells to detect intracellular pathogens, such as viruses and some protozoa, which are able to replicate inside host cells. This mode of antigen recognition is less relevant for extracellular parasites or pathogens, which are not directly present within host cells.

The Antigen Receptor on a T Cell Recognizes a Degraded