Review of the comparative pathology of the Hoeppli phenomenon shows that it is correlated with substantial egg loads, appears during the later part of the acute primary state of infection, arises around mature eggs, occurs selectively in organs with large egg loads and affects a fraction of eggs not exceeding 10 percent at any time.
Immunofluorescent studies in Mastomys coucha show that the Hoeppli corona contains both egg antigen and fixed host globulin, and is therefore an antigen-antibody complex. Within the complex, there is a gradient of antigen-antibody concentration, with antibody excess in the periphery. The precipitate pursues a sequence of maturation and degradation concomitant with the evolution of the pseudotubercle, during which additional host and parasite components may be incorporated into it. The characteristics of the Hoeppli phenomenon in three schistosome species, its relationship to the in vitro circumoval precipitate, and to stellate precipitates in other granulomatous diseases are discussed, and it is postulated that the Hoeppli phenomenon is an auxiliary mechanism of antigen sequestration invoked by the heavily infected host when antigen production against certain egg fractions attains a critical concentration and ratio resulting in precipitation of an antigen-antibody complex in vivo.