B Cell Membrane Proteins Molecules involved in Ag presentation To activate T cells Ag must be presented by APC B cells (like other APC)act as APC for T cells B cells share important characteristics with other APC B cells express class II MHC molecules constitutively (always expressed) Increase MHC class II expression by IL-4 Present Ag to CD4+T cells(helper T cells) MHC class II is expressed on all cells in the B cell lineage apart from the pro-B cell B Cell Membrane Proteins Molecules involved in Ag presentation ◼ To activate T cells Ag must be presented by APC ◼ B cells (like other APC) act as APC for T cells ◼ B cells share important characteristics with other APC ◼ B cells express class II MHC molecules constitutively (always expressed) ◼ Increase MHC class II expression by IL-4 ◼ Present Ag to CD4+ T cells (helper T cells) ◼ MHC class II is expressed on all cells in the B cell lineage apart from the pro-B cell