Fibroblasts and eosinophils in normal fibroplasia of ferret vulval skin, shown by light and electron microscopy; with special reference to eosinophil degranulation.

In order to compare aspects of normal fibroplasia with reports for pathologically fibrotic tissue, light and electron microscopic observations were made on ferret vulval skin, which proliferates markedly with the onset of estrus and regresses equally fast after mating. Estrous tissue, which contained hypertrophied fibroblasts, new collagen, elastic fibers and ground substance, was invaded by numerous eosinophils with extensive release of granules. Eosinophil degranulation was both extra- and intracellular; some cells, completely disintegrated, had released all contents into the extracellular matrix. Extruded granules reacted positively for major basic protein. In regression, diminished fibroblasts incorporated collagen fibrils. Many of the features seen in this normal fibroplasia in ferret vulval skin are similar to those in pathologic situations. Thus, in particular, the presence of degranulating eosinophils in pathologic fibrosis does not necessarily indicate that they are the cause of the disease. Our information and that from other sources implies a role for eosinophils in connective tissue change.