IFN-gamma down-regulates MHC expression and antigen processing in a human B cell line.

IFN-gamma is a crucial mediator in the induction of cell-mediated Th1-type responses but is predominantly a negative regulator of B cell differentiation and proliferation. This cytokine is therefore a key factor in determining Th1 vs Th2 differentiation. This study investigates the action of IFN-gamma in modulation of HLA-DR expression and Ag presentation by EBV-transformed human B cell lines. In contrast to its action on the monocyte/macrophage, IFN-gamma down-regulates surface MHC expression on these B cells, and this regulation is posttranscriptional. In parallel with MHC down-regulation, there is a reduced capability to process and present exogenous protein and peptide Ag to T cell hybridomas. IFN-gamma does not change the rates of fluid phase endocytosis or exocytosis in this model system but correlates with an up-regulation of the lysosomal enzymes cathepsins B and D.