IFNG and lymphoma: In order to further define the mechanistic basis of the lack of MHC II expression, we performed fusion experiments using either the BALB/c-derived A20 lymphoma cell line, which constitutively expresses MHC II (I-Ad/I-Ed), or the C57BL/6-derived B16 melanoma (I-Ab), which expresses MHC II upon IFN-γ stimulation (cfr.