A simple method to eliminate the antigenicity of surface class I MHC molecules from the membrane of viable cells by acid treatment at pH 3.

We describe here a simple, reproducible method which specifically eliminates the antigenicity of surface class I major histocompatibility complex (MHC) molecules by acid treatment at pH 3 from the membrane of viable cells. When fresh mononuclear cells (MNC) or established cultured cell lines were treated at 4 degrees C for 2 min with citric acid buffer at pH 3 containing 1% bovine serum albumin, the antigenicity of class I MHC molecules, but not those of class II MHC and the other non-MHC antigens, was eliminated from the surface membrane without significant cell death. This method was effective for both human and murine cells with various origins. Monoclonal and polyclonal antibodies were used to identify the expression of surface antigens in conjunction with immunofluorescence tests. The eliminated antigenicity of human class I MHC antigens (i.e., HLA-A,B,C) on MNC regenerated when cells were incubated in the medium at 37 degrees C for 10 h. The pretreatment of cells with emetine (10(-4) M), a protein synthesis inhibitor, was found to be effective in inhibiting this regeneration. The acid treatment method might be useful for future studies on the functional characterization of surface class I MHC antigens.