Which statement is NOT true about B cells?

• A. They can recognize native antigen without MHC restriction via BCR
• B. They can produce antibodies
• C. They can present antigen to helper T cells
• D. They originate from megakaryocytes

Answer: (D)

B cells are key players in humoral immunity and have three main abilities: they can recognize native antigen directly through their surface B cell receptor (BCR) without needing antigen presentation by MHC, they can differentiate into antibody-secreting cells to produce antibodies, and they can present processed antigen to helper T cells via MHC class II to receive T cell help. The BCR binds conformational epitopes on intact antigens, which is why this recognition isn’t MHC-restricted, unlike T cell receptors that require peptide antigens presented by MHC molecules. After antigen binding, B cells internalize the antigen, process it, and present peptides on MHC II to CD4+ T helper cells, receiving signals that drive activation, class switching, and affinity maturation. They can then become plasma cells that secrete antibodies or memory B cells for faster responses upon re-exposure. The statement about origin is not true: B cells do not originate from megakaryocytes. Megakaryocytes are platelet precursors from the myeloid lineage, while B cells arise from hematopoietic stem cells in the bone marrow through the lymphoid lineage.