- Volume 9, Issue 3, 1970

Treatment of Semliki Forest virus with Nonidet-P40, sodium deoxycholate or Tween 80 + ether destroyed virus infectivity but preserved complement fixing, haem-agglutinating and neutralizing antibody blocking activities. All treatments split the virus into intact cores and fragments of envelope, but Nonidet gave the best separation of these components. Only the virus envelope had haemagglutinating and neutralizing antibody-blocking activities. Immunodiffusion tests showed that the envelope and core proteins were serologically distinct.

Further treatment of envelope fragments with dilute trypsin liberated at least three antigens, which could be separated by column chromatography. In immuno-diffusion tests, antigens 2 and 3 were serologically distinct, but both gave reactions of partial identity with antigen 1. All antigens fixed complement, but only antigen 1 was associated with haemagglutinating and neutralizing antibody-blocking activities. Sephadex gel filtration indicated that antigen 1 had a particle weight greater than 200,000 daltons, that antigen 3 had a molecular weight of about 9000, and that antigen 2 was intermediate in size.

Antiserum was prepared in rabbits against purified haemagglutinin obtained from A0/bel virus. The antiserum had potent virus-neutralizing and haemagglutination-inhibiting activity, but was free of antibody to A0/bel neuraminidase or to influenza A type-specific ribonucleoprotein. In immunodiffusion tests, the anti-haemagglutinin serum gave precipitin reactions with all A0 and A1 virus strains tested but did not react with human A2 viruses or avian or porcine influenza A viruses. The studies suggested a close immunological relationship between the haemagglutinins of A0 and A1 influenza viruses which was not revealed by haemagglutination-inhibition tests.

Four single-sporangium isolates of Olpidium brassicae were inoculated on 14 different plant species to determine their ability to infect and reproduce in each host and their ability to transmit two tobacco necrosis virus isolates. Two O. brassicae isolates, one from lettuce and one from tomato, were able to reproduce in most hosts and transmitted both tobacco necrosis virus isolates to all hosts. By contrast, a mustard isolate reproduced in only six species and was not a vector of tobacco necrosis virus. An oat isolate reproduced in six species (three in common with the mustard) and was a poor vector, transmitting one tobacco necrosis virus isolate to only two hosts and not transmitting the other tobacco necrosis virus isolate to any host.

Zoospores of the different fungus isolates were mixed with suspensions of virus, washed, negatively stained, and examined in the electron microscope. Virus adsorbed tightly to the surface membranes (plasmalemma of the body and axonemal sheath) of zoospores of isolates that transmitted it, but not to those of the non-vector (mustard) isolate. Zoospores of the poor vector (oat) isolate adsorbed fewer particles of the tobacco necrosis virus isolate they transmitted than did those of good vectors and did not adsorb the other tobacco necrosis virus isolate. Most, but not all, of the observed specificity of transmission of tobacco necrosis virus seems to be associated with the ability or inability of zoospores to adsorb the virus on their surfaces. None of these isolates adsorbed particles of turnip yellow mosaic, tomato bushy stunt or cucumber necrosis viruses. O. brassicae zoospores also adsorbed satellite virus particles. Zoospores of Olpidium cucurbitacearum adsorbed particles of cucumber necrosis virus, but not of tobacco necrosis virus, to their surfaces. Thus, in vitro acquisition consisted of a tight adsorption of virus to the zoospore surface membranes in each of the three known instances of this type of relationship.

Kinetic haemagglutination-inhibition tests were used to investigate possible antigenic variation between four strains of rubella virus which had been isolated in different years and in different geographical areas. No significant differences were detected using hyperimmune rabbit sera and human sera obtained following both naturally acquired infection and vaccination with an attenuated rubella vaccine. These results suggest that major antigenic variation is unlikely to constitute a problem with rubella.

Infectivity titration, sedimentation analysis in sucrose gradients and electron microscopy have been used to study virus maturation following the reversal of the inhibition of vaccinia virus growth by rifampicin.

Electron-dense inclusions containing tubular structures develop in the cytoplasm of infected BHK 21/C 13 cells maintained in rifampicin, but the formation of immature and mature virus particles is prevented. The removal of rifampicin is followed by a rise of the virus infectivity. Spicule-covered membranes appear at the periphery of the inclusions and both immature and mature virus particles are seen. A proportion of the DNA synthesized in the presence of rifampicin is incorporated into particles and becomes resistant to deoxyribonuclease I. If protein synthesis is inhibited, spicule-covered membranes and immature particles appear but no mature particles are seen; the virus infectivity does not increase and the DNA remains susceptible to deoxyribonuclease I. It is suggested that rifampicin binds reversibly to a virus-specified protein, thereby preventing the formation of immature virus particles. Possible effects of rifampicin on the subsequent stages of virus maturation are discussed.