Conventional and immunocolloidal gold electron microscopy of eight simian retroviruses closely related to human T-cell leukemia virus type I.

Simian retroviruses closely related to human T-cell leukemia virus type I (HTLV-I) were isolated from 8 species, examined by both conventional and thin section immunocolloidal gold electron microscopy, and compared with HTLV-I. Mature forms of simian viruses were found in extracellular aggregates and within cytoplasmic vacuoles. They were morphologically similar to each other and to HTLV-I. They consisted of a seemingly smooth envelope and a centrally located nucleoid. Their size varied considerably among species and also within the same species; this is characteristic of this group of retroviruses. No budding particles of simian viruses were observed. Thin section immunocolloidal gold electron microscopy using various human and simian sera showed that simian viruses were antigenically related to each other and to HTLV-I. One drawback of this otherwise very useful technique was the difficulty in identifying virions because of the poor preservation of their fine structure by fixation with glutaraldehyde alone. This was overcome by using materials prepared for conventional electron microscopy, in which virions showed weak but specific reactions with gold particles after deosmification and antigen restoration with sodium metaperiodate.