THE BIOLOGICAL, IMMUNOLOGICAL, AND PHYSICOCHEMICAL CHARACTERIZATION OF A TRANSMISSIBLE AGENT CAPABLE OF INDUCING DNA AND THYMINE DEGRADATION IN CULTURED HUMAN CELLS

Experiments designed to characterize an unidentified transmissible agent brought forth the following findings: The cytopathology consisted of the formation of intranuclear globules, collapse of the involved nuclei, and the extrusion of nuclear materials. The relatively dormant primary human amnion cells were less susceptible than the rapidly growing cell lines. Similarly, the slowly multiplying ribose variants were less susceptible than their corresponding parent cell lines. Interferon-like activity was released from infected cells. Infectivity was readily demonstrated following storage at 0–4°C for at least 8 months or at 37°C for at least 2 weeks. Freeze-thawing, however, markedly reduced or completely destroyed its infectivity. Infectivity was destroyed completely by ether and chloroform; partially by desoxycholate, and not affected by trypsin, papain, RNAse, DNAse, hyaluronidase, lysozyme, lecithinase, or pancreatic lipase. The rate of inactivation by 0.025 per cent formalin was much slower than that of vaccinia and herpes viruses. Its synthesis was suppressed by 5-fluorodeoxyuridine. This suppression was not reversed by thymidine and/or uracil. Heat-stable neutralizing antibody could not be demonstrated in 379 human and animal serums, in human gamma globulins, or in serums from animals "immunized" with this agent. Heat-labile inhibitors (lipoprotein-like) capable of inhibiting the infectivity of this agent were demonstrated in 154 of the 157 serums tested. Experimental evidence indicated the non-identity of this ubiquitous inhibitor and the properdin system. The non-infectious complex between this agent and the ubiquitous serum inhibitor may be dissociated (hence, become infectious) by simple dilution. Repeated attempts to reisolate a similar agent have not been successful. We have hypothesized that this agent is a virus consisting of DNA wrapped in a surface coat rich in lipid, and suggest that this virus be referred to tentatively as a lipovirus.