Which cells express MHC Class II proteins?

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Multiple Choice

Which cells express MHC Class II proteins?

Explanation:
The key idea is which cells use MHC Class II to show external (exogenous) antigens to helper T cells. MHC Class II molecules are expressed mainly on professional antigen-presenting cells—dendritic cells, macrophages, and B lymphocytes. These cells grab extracellular proteins, process them in endosomal compartments, and load peptide fragments onto MHC II to present to CD4+ helper T cells, which is how helper responses are activated. That’s why the best choice includes antigen-presenting cells and lymphocytes. B cells are lymphocytes that can act as APCs and express MHC II, aligning with the concept. The other cell types listed—neurons and muscle fibers; red blood cells and platelets; smooth muscle and endothelial cells—don’t regularly display MHC Class II. Neurons and muscle typically rely on MHC I; red blood cells lack nuclei and MHC II expression; endothelial and smooth muscle can express MHC II only under specific inflammatory conditions, not as a standard feature.

The key idea is which cells use MHC Class II to show external (exogenous) antigens to helper T cells. MHC Class II molecules are expressed mainly on professional antigen-presenting cells—dendritic cells, macrophages, and B lymphocytes. These cells grab extracellular proteins, process them in endosomal compartments, and load peptide fragments onto MHC II to present to CD4+ helper T cells, which is how helper responses are activated.

That’s why the best choice includes antigen-presenting cells and lymphocytes. B cells are lymphocytes that can act as APCs and express MHC II, aligning with the concept. The other cell types listed—neurons and muscle fibers; red blood cells and platelets; smooth muscle and endothelial cells—don’t regularly display MHC Class II. Neurons and muscle typically rely on MHC I; red blood cells lack nuclei and MHC II expression; endothelial and smooth muscle can express MHC II only under specific inflammatory conditions, not as a standard feature.

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