The major histocompatibility complex proteins are found on the surface of what type of cells?

• A. B Cells
• B. T Cells
• C. Null Cells
• D. Polymorphonuclear Leukocytes

Answer: (B)

MHC proteins function to display peptide antigens to T cells, and there are two main classes with distinct patterns of expression. Class II MHC molecules appear on professional antigen-presenting cells, including B cells, macrophages, and dendritic cells, enabling these cells to present antigen to CD4+ helper T cells. Among the options given, B cells are the ones that routinely express MHC proteins on their surface to present antigen. T cells themselves are not typical antigen presenters; they recognize MHC-peptide complexes rather than presenting them. Neutrophils and NK cells do not serve as classical MHC II-presenting cells. So, B cells are the best fit for surface MHC expression in this context.