Naturally Resistant Human Cells

Replication of virus can take place in naturally resistant cells, provided that measures are taken to circumvent the barrier to infection presented at the cell surface. Holland and his associates (9) initiated infection in resistant chick embryo cells with poliovirus ribonucleic acid (RNA). Subsequently Enders and his co-workers (4) and Neff and Enders (11) showed that complete poliovirus replicates in hamster cells and chick embryo cells exposed to inactivated Sendai virus. It was suggested that the virus was incorporated into the cytoplasm of these naturally resistant cells during the Sendai virus-induced process of cell fusion in which the cellular membrane is impaired or ablated. It was proposed that this technique might be employed as a means of isolating agents which have not yet been cultivated in vitro. The foregoing observations raised the question of whether the natural barrier in cells resistant to infection by deoxyribonucleic acid (DNA) viruses, which replicate in the nucleus rather than in the cytoplasm, could also be overcome by cell fusion. For it seemed that with such intact agents the nuclear membrane might provide a second barrier to successful entry of the virus into the only cellular compartment in which replication can take place. An answer to this question might not only extend the potential usefulness of Sendai virus in overcoming cellular resistance but also help to define other barriers to infection that may exist in the naturally insusceptible cell. Feline herpesvirus (FHV; 3) was selected as the test organism, since this agent replicates in vitro to high titers and produces easily recognizable intranuclear inclusion bodies in feline kidney (FK) cells but has been found to exhibit no detectable effect on cells from a variety of other species (2, 10). MATERIALS AND METHODS