Prevalence of type R virus-like particles in clones of BHK-21 cells.

The BHK-21 line of Syrian hamster fibroblasts (1) is used widely for research on viruses and on the neoplastic transformation of cells in vitro. Bernhard and Tournier (2) were the first to describe a virus-like particle in BHK-21 clone 13 (BHK-21/13) cells. Subsequent studies have confirmed the presence of this particle in BHK-2l/ClS/TCG/A (5), BHK-21F (4), and BHK-21/13S (5). A detailed study of the morphogenesis of this virus-like particle was reported by Thomas and his associates (6). Despite the detection of such particles in several clones of BHK-21 cells, and cells derived from spontaneous or induced hamster tumors (2, 7, 8), the widespread occurrence of this virus-like particle has received only limited recognition. The virus-like particle in question is distinguished by the presence of characteristic electron-dense radial structures which appear to emanate from the nucleoid. The radial structure of the particle differentiates it from the Bernhard type C virus particle characteristic of the murine leukemia viruses. To avoid confusion we shall refer to the hamster virus-like particle as a type R (radial) virus-like particle. It is the purpose of this communication to document the presence and distribution of the type R virus-like particle in all clones of BHK-21 studied to date and to alertinvestigators to the presence of this particle. The clones of BHK-21 cells selected for this study are listed in Table 1. The origins of these clones of BHK-21 and other clones known to contain type R virus-like particles have been previously described in the literature (g-12). Two other established hamster cell lines, HaK and RPMI-1846 (IS), and normal and virus-transformed hamster cells were also examined. All hamster cells with the exception of RPMI-1846 cells were grown as monolayers in Eagle basal medium (Earle salts) supplemented with 15% fetal bovine serum. RPLMI-1846 cells were propagated in McCoy 5A medium (modified) containing 20% fetal bovine serum. Incubation was carried out at 37” in an atmosphere of 4 % C02-96 % air. Tissues or tissue culture cells for electron microscopy were fixed in 2.5 % phosphatebuffered glutaraldehyde, postfixed in veronal-acetate buffered 1% 0~0~ and embedded in Epon 812. Thin sections were cut with a Porter-Blum MT-l microtome and stained with a saturated aqueous solution of uranyl acetate and lead citrate prior to ex-