Which cellular compartment processes a peptide recognized by a T-lymphocyte clone from influenza virus?

The correct answer is the endosomes. In the context of T-cell activation and the presentation of viral peptides, it is important to understand the pathway of antigen processing. For CD4+ T lymphocytes, which recognize peptides presented by MHC class II molecules, the processing of antigens typically occurs within endosomal compartments.

When an antigen, such as a protein from the influenza virus, is internalized by professional antigen-presenting cells (APCs) through endocytosis, it is transported into endosomes. Here, it is processed into smaller peptide fragments. These peptides are then loaded onto MHC class II molecules within the endosomes. The MHC-peptide complexes are subsequently transported to the cell surface, where they can be recognized by T-lymphocytes.

Understanding this pathway highlights why endosomes play a crucial role in the processing of peptides that T-lymphocyte clones recognize, particularly for those that are derived from extracellular sources, such as viruses that have been taken up by engulfing cells.

The other compartments mentioned, like the cytosol and the endoplasmic reticulum, are more involved in the processing of different antigen types. The cytosol is primarily where endogenous antigens (e.g., viral proteins synthesized within the