Ultrastructural observations on the fate of Brugia malayi in jirds previously vaccinated with irradiated infective stage larvae.

Vaccination of inbred jirds (Meriones unguiculatus) with 60cobalt radiation-attenuated Brugia malayi infective stage larvae (L3) protected against homologous challenge given either subcutaneously (sc) or by the intraperitoneal route (ip). At necropsy numerous nodules were recovered from the peritoneal cavities of jirds which had been vaccinated sc and challenged ip. Histopathologic analysis showed these to be granulomas containing dead and dying larvae and transmission electron microscopy showed that eosinophils were present in high numbers around and within the larvae. Structural damage to the L3 cuticle was apparent in discrete areas and eosinophils actively entering the breached cuticle at the time of fixation were observed. Coalescence of eosinophil secretion granules and the formation of degranulation vacuoles were seen in eosinophils throughout the granulomas. Degranulation resulted in the deposition of electron-dense material on the surface of the larval cuticle. The jird vaccine model for B. malayi thus appears to be a potentially useful tool for investigation of immune mechanisms in filariasis.