Pentastomid nymph from the brain of a squirrel monkey (Saimiri sciureus). II. Morphology of the host response.

A Porocephalus nymph found in the meninges of a squirrel monkey was encapsulated by connective tissue cells and fibrils presumably derived from the pia mater. The capsule was composed of an inner layer (IL) adjacent to the nymphal integument and an outer layer (OL) adherent to the brain surface. Separating the two layers was a capsular space. The IL was lined by a granular material adjacent to the nymph surface and possessed impressions of annulae and the apical pits of chloride cells. The surface of IL facing the capsular space was characterized by a monolayer of cells possessing extensive anastomosing plasmalemmal processes. The OL was composed of several tiers of fibroblasts and associated collagen fibrils that adhered to the brain surface in the form of a thickened pia mater. It is suggested that the capsule was formed by a modification of the pia that isolated the nymph and created an "intracapsular space" with specialized lining cells to facilitate fluid exchange.