IMMUNOCYTOCHEMICAL LOCALIZATION OF HEPARIN IN SECRETORY GRANULES OF RAT PERITONEAL MAST-CELLS USING A MONOCLONAL ANTI-HEPARIN ANTIBODY (ST-1)

We performed immunogold labeling with an ST-1 monoclonal antibody (IgM ), specific for intact heparin, to define the subcellular localization of heparin in mast cells. Rat peritoneal mast cells were fixed by a m odified Karnovsky method and embedded in Araldite. Ultrathin sections were first treated with sodium periodate and then sequentially incubat ed with MAb ST-1, rabbit anti-mouse IgM, and protein A-gold. By transm ission electron microscopy, gold particles were localized inside cytop lasmic granules of peritoneal mast cells. In contrast, with the same p rocedure, no labeling was observed in mast cells from rat intestinal m ucosa. Control sections of rat peritoneal or intestinal mucosa mast Ma st cells cells treated with an irrelevant MAb (IgM) did not show any l abeling. Treatment with nitrous Heparin acid abolished the reactivity of MAb ST-1 with peritoneal mast cells. These results Granules show th at different mast cells can be identified regarding their heparin cont ent by immunochemical procedures using MAb ST-1.