Specificity of 2 anti-FcRH1 monoclonal antibodies. (A) Human 293T cells were transiently transfected with FcRH1 to FcRH5 expression vectors and stained with 3B4 (thick gray line) or 5A3 (thick black line) monoclonal antibodies for immunofluorescence analysis. Cell surface expression of FcRH2 to FcRH5 was confirmed by the use of specific monoclonal antibodies against each molecule. (B) Recombinant FcRH proteins and the chicken Ig-like receptor (CHIR) were immunoblotted with anti-FcRH1 (5A3).