CRYOSUBSTITUTION TECHNIQUE REVEALS NEW MORPHOLOGY OF FLAVIVIRUS-INDUCED STRUCTURES

Cryotechniques in combination with electron microscopy were used in an attempt to obtain more precise morphological details of flavivirus-in duced structures. From conventional chemical fixation procedure, proli feration of endoplasmic reticulum, formation of microtubule paracrysta ls and clusters of smooth membrane vesicles (with 'thread-like' enclos ures) were observed. These induced changes are typical for flavivirus infections. The images obtained from cryosections were disappointing a s the structures were not well preserved. On the other hand, cryosubst ituted-infected cells gave revealing images of the virus-induced struc tures. The most obvious difference between the cryosubstituted and che mical fixed processes was on the morphology of the 'thread-like' struc ture. The 'thread-like'. structures instead appeared as dense cores. T he morphology of the virus particles was also better defined. The enve lope of the virus appeared clearly differentiated from the nucleocapsi d. The most important finding was that the cryosubstituted technique w as able to preserve the structures of the flavivirus nucleocapsids whi ch so far has not been convincing reported with chemical processing.