Light and electron microscopy immunolocalization of BFGF in eosinophils in chronic inflammatory tissues

Eosinophils are involved in several inflammatory disorders of unknown etiology. However, their exact contribution to inflammation remains largely unknown. Recent studies have shown that eosinophils produce several cytokines/growth factors that are important inflammatory mediators. In the process of identifying cellular sources of basic fibroblast growth factor (bFGF), a potent angiogenic and mitogenic polypeptide, we examined tissue samples from patients with pemphigoid or nasal polyposis, as well as dermal granuloma from rats. In all samples examined, a subpopulation of both ultra- and extra-vascular eosinophils exhibited strong cytoplasmic immunoreactivity to ami-bFGF antibodies. Their identity was confirmed in adjacent 2-(im sequential sections. By electron microscopy, eosinophils were identified by their typical cytoplasmic granules containing a crystalline core. Strong immunostaining for bFGF was found in the granules (excluding the crystalline core), and moderate staining was found in the nucleus. In contrast, no staining was found in lymphocytes or plasma cells in the same tissue. Furthermore, all procedural controls were devoid of staining. These results link bFGF to eosinophils in chronic inflammatory tissues and suggest that they may play a role in regulating tissue bFGF levels. An investigation is currently in progress to determine if bFGF mRNA can also be found in thesft ensinnnhik and if hFGF levels in ensinnnhils and rorrelateri with disease state.