Intracytoplasmic inclusions in foetal lamb kidney cells infected with Wesselsbron virus

Abstract

An electron microscopic study of the intra-cellular development of Wesselsbron virus, a group B Arbovirus, has been undertaken. Secondary cultures of foetal lamb kidney cells infected with Wesselsbron virus were harvested at daily intervals, fixed in 1 ~ osmium tetroxide, dehydrated and embedded in methacrylatc. Ultrathin sections were stained with lead citrate and examined in a Siemens Elmiskop I electron microscope. In control uninfected cultures of foetal lamb kidney cells the intracellular organe]les were clearly identified and regular in appearance. Nuclear chromatin was evenly distributed and the cytoplasm not vacuolated. Infected cells did not show any distinct change until 48 hours after infection, when the nuclei appeared closely packed and displayed a margination of their chromatin. The most striking observation was the appearance of many unusual orderly-patterned inclusions in "crystalline-like" array, in the cytoplasm of the cells. The regularity and the apparent three dimensional nature of these inclusions is illustrated in Fig. 1. They appeared to be closely associated with the endoplasmic reticulum which showed gross vesiculation in the vicinity of the arrays. The varying organization within the inclusions is clearly presented in Fig. 2. Sections through different planes show areas of hexagonal units in "honey-comb" formation (A) and four-sided units in reticulate array (B). This may suggest an arrangement of short hexagonal cy]inders