John L. Riggs

Photochemical inactivation of DNA and RNA viruses by psoralen derivatives.

Western equine encephalitis virus, and RNA virus, and herpes simplex virus type I, a DNA virus, were efficiently inactivated in less than I min by exposure to long-wave ultraviolet light (320 to 380 nm) in the presence of several psoralen derivatives. The psoralen photochemical reaction was chosen for study due to its known specificity for nucleic acids. Neither the light nor any of the drugs alone caused appreciable inactivation. The inactivation kinetics and dependence on light intensity and on different derivatives of psoralen were studied. The high solubility of a new aminomethyl psoralen derivative was found to be advantageous in the photochemical inactivation of the RNA virus, but was not in the case of the more easily inactivated DNA virus. Within its limited solubility range trimethylpsoralen was superior to its aminomethyl derivative on a molar basis for the inactivation of both types of viruses under most of the conditions studied.

Neutralization kinetics of western equine encephalitis virus by antibody fragments

Abstract Antibody against western equine encephalitis virus from the isolated and purified IgG fraction of hyperimmune rabbit serum was digested with papain or pepsin and the neutalizing ability of the resulting 5S (F(ab′)2) and 3·5S (Fab I, II) fragments comparerd to that of the 7S molecule. By plaque reduction assay, the neutralizing capacity and neutralization kinetics of the F(ab′)2 fragment was as effective as the 7S molecule even if the protein concentration of the F(ab′)2 was lowered to approximate the mole concentration of the 7S molecule. The neutralizing ability of the Fab fragments was less effective, the kinetics of neutralization slower and the nonneutralizable fraction larger even when the concentration was adjusted to two times that of the whole molecule. An initial shoulder in the neutralization kinetic curve was seen with all the preparations if neutralization was carried out at 4°C but it was less prominent or absent at 37°C. No significant dissociation of the 7S-virus, F(ab′)2 or Fab II-virus complexes occured on dilution or sonication at the protein concentrations studied. At the lowest concentration of Fab I, significant dissociation of the virus-Fab I complex did occur after 5 min sonication, resulting in a 24–37 per cent nonneutralizable fraction as compared to 3 per cent after the initial incubation period. No significant protection of infant mice occureed with any of the fragments after an hour incubation of the virus-fragment mixtures at 37°C.

Distinction between envelope antigens of murine xenotropic and ecotropic type C viruses by immunoelectron microscopy.

The indirect ferritin-labelled antibody technique was used to determine the reactivity of an antiserum prepared against the NZB xenotropic virus with three murine xenotropic viruses, a feline xenotropic virus and a murine ecotropic virus. The envelope antigens of the xenotropic type C viruses isolated from the NZB, NIH Swiss and C57L mice were tagged with ferritin. The feline RD114 virus was not. Gross murine leukaemia virus was tagged, but only at high serum concentrations. The cross-reactivity titre of Gross virus to anti-NZB serum was removed by a serum dilution which was still reactive to xenotropic viruses. This difference in reactivity titres between a xenotropic and an ecotropic virus was sufficient to distinguish one from the other in doubly infected cultures. Specific tagging of membrances of cells infected by xenotropic virus was also observed.

Ferritin-labelled antibody study of RD-114 virus.

Summary Comparative studies by the ferritin-labelled antibody technique showed differences between the surface antigens of RD-114 and feline leukaemia viruses (FeLV). Guinea pig and rabbit antisera to RD-114 virus reacted with RD-114 virus but not with FeLV. Dog antiserum to FeLV reacted with FeLV but not with RD-114 virus.