Immunohistochemical characterization of reactive and neoplastic mast cells.

Mast cells are connective tissue elements likened to unicellular endocrine organs because of the wide diversity of physiologic and pathologic events associated with the secretion of biologically active compounds. Using an immunoperoxidase method (PAP), we studied tissue from patients with benign and malignant systemic mastocytosis and with a variety of reactive conditions. The following immunoreactive antigens were identified in mast cells: a heparinlike compound or compounds (HLC), prostaglandin, serotonin, and fibronectin. HLC is constantly present, staining mast cells in a granular fashion from most lesions. Serotonin and prostaglandin stain in a diffuse cytoplasmic manner in occasional lesions. Fibronectin is found in a surface location in selected cases. We found no clear association between the immunoreactivity of one compound in mast cells and one clinical symptom, e.g., HCL with bleeding, prostaglandin, or serotonin with systemic vasomotor activity or fibronectin with increased tissue fibrosis. However, patients with localized and systemic disease had symptoms that might have been attributed to more than one compound. Only occasional patients with reactive conditions showed such symptoms. The presence of these compounds, either alone or in combination, did not separate benign from malignant conditions. Other cells within selected tissues also stained with the antibodies tested. Despite the lack of exclusivity, these antibodies are useful in identifying mast cells within tissue sections and may have a role in the study of mast cell constituents.