Identical twins have the same set of MHC proteins.

• A. True
• B. False
• C. Not necessarily
• D. They differ

Answer: (A)

Identical twins originate from the same fertilized egg, so they share essentially the same genome, including the MHC gene region. The set of MHC proteins a person can present is determined by which MHC alleles they carry. Because identical twins inherit the same MHC alleles, they have the same repertoire of MHC class I and class II proteins on their cells. The actual expression levels can vary a bit due to epigenetic factors or disease states, but the identity of the MHC proteins themselves remains the same. So the statement is correct because the MHC protein set is defined by inherited genes, which are identical in identical twins.