RP105 is mainly expressed on B cells in mantle zones. Frozen sections from a human tonsil were stained with the MHR73 MoAb. (A) RP105⁺ B cells are mainly located in a mantle zone that surrounds a germinal center where expression of RP105 is dull or negative (original magnification × 50). (B) Higher magnification (original magnification × 200) of a boundary between the mantle zone and the germinal center of (A). No significant signal was observed by staining with the second reagent alone.