Ultrastructural aspects of infiltrated eosinophils in bullous pemphigoid

By scanning (SEM) and transmission electron microscopy (TEM), we evaluated the infiltrated eosinophils in lesions at various stages of clinical development from patients with bullous pemphigoid (BP) and eosinophilia. Visualized by SEM, numerous inflammatory cells migrated through the cutaneous basement membrane into the cavity of newly formed blisters 12 to 24 hrs after formation. Many migrating cells attached to the reverse side of the bullous cavity, and some basal cells shed into the cavity. As the bullae developed 24 to 48 hrs after formation, the reverse surface of the bullous cavity became predominantly composed of these migrating cells and the exposed squamous cells. The migrating cells had villi, ruffles and ridge-like profiles on their surfaces, which were suggested eosinophils. By TEM in the same lesions, many morphologically activated eosinophils were seen to have passed through the basement membrane into the newly formed blisters; they exhibited spheroidal cytoplasmic granules with less dense crystalloid cores and intracellular channels. Eosinophils infiltrating in the developed bullous cavity directly adhered to basal cells and released their granule contents onto these target cells. These findings suggest that inflammatory cells, especially eosinophils, may amplify the formation of dermal-epidermal separation in BP lesions.