Colocalization of sTNFR1 with a matrix protein (RMCP) and a membrane-associated protein (lgp120) of secretory lysosomes. Ultrathin cryosections from RBL cells transfected with sTNFR1-tm-Y were labeled accordingly. (A) Labeled with rabbit anti-sTNFR1. (B) Double labeled with rabbit anti-sTNFR1 (10 nm) and mouse anti-RMCP (15 nm). (C) Double labeled with rabbit anti-sTNFR1 (10 nm) and rabbit anti-lgp 120 (15 nm). (A) Area of a cell showing granules highly labeled with sTNFR1. The Golgi (G) and the trans Golgi network (TGN) also are labeled. (B) Granules are shown double labeled for sTNFR1 and RMCP on the matrix. (C) A granule is seen with labeling for lgp 120 on the membrane and for sTNFR1 on the matrix. n indicates nucleus. Bar, 200 nm.