Development of the granulomatous response in murine toxocariasis. Initial events.

The cellular evolution of the persisting, muscle-associated granuloma in murine toxocariasis (visceral larva migrans) was chronicled for 11 weeks by light and electron microscopy. The initial granuloma consisted primarily of eosinophils and appeared to develop from the acute inflammatory infiltrate. During the ensuing 48 hours, most of the eosinophils appeared to loose their granules and disintegrate. The resulting cellular debris was then taken up by newly arrived macrophages which become the predominant mononuclear cell in the lesion by 28 days of infection. By 11 weeks, the granuloma had become a fibrotically encapsulated epithelioid granuloma surrounding the inciting larva. This histologic reaction is compared with the liver granulomatous response to Toxocara and to the well-characterized schistosome egg granuloma. A possible delayed hypersensitive etiology for the Toxocara granuloma is suggested.