TYPE-II AND TYPE-III RECEPTORS FOR IMMUNOGLOBULIN-G (IGG) CONTROL THEPRESENTATION OF DIFFERENT T-CELL EPITOPES FROM SINGLE IGG-COMPLEXED ANTIGENS

T cell receptors on CD4(+) lymphocytes recognize antigen-derived pepti des presented by major histocompatibility complex (MHC) class II molec ules. A very limited set of peptides among those that may potentially bind MWC class II is actually presented to T lymphocytes. We here exam ine the role of two receptors mediating antigen internalization by ant igen presenting cells, type IIb2 and type III receptors for IgC (Fc ga mma RIIb2 and Fc gamma RIII, respectively), in the selection of peptid es for presentation to T lymphocytes. B lymphoma cells expressing reco mbinant Fc gamma RIIb2 of Fc gamma RIII were used to assess the presen tation of several epitopes from two different antigens. 4 out of the 1 1 epitopes tested were efficiently presented after antigen internaliza tion through Fc gamma RIIb2 and Fc gamma RIII. In contrast, the 7 othe r epitopes were efficiently presented only when antigens were internal ized through Fc gamma RIII, but not through Fc gamma RIIb2. The capaci ty to present these latter epitopes was transferred to a tail-less Fc gamma RIIb2 by addition of the Fc gamma RIII-associated gamma chain cy toplasmic tail. Mutation of a single leucine residue at position 35 of the gamma chain cytoplasmic tail resulted in the selective loss of pr esentation of these epitopes. Therefore, the nature of the receptor th at mediates internalization determines the selection of epitopes prese nted to T lymphocytes within single protein antigens.