We recently reported the cultivation in organ cultures of a virus, B814, which caused colds in volunteers but could not be detected or propagated in tissue cultures (Tyrrell and Bynoe, 1965). Hamre and Procknow (1966) have discovered a " new " virus in the respiratory tract of six students suffering from colds. There was a slight viral cytopathic effect in tissue cultures of human embryo kidney cells, but the virus was subsequently adapted to the WI-38 strain of human embryo fibroblasts. Both of these viruses were ether-labile but apparently unrelated serologically to any known myxoviruses. It now appears that they are morphologically identical and indistinguishable from the viruses of avian infectious bronchitis , and mouse hepatitis Materials and MethodsVirus.-The 229-E virus was received from Dr. Hamre as tissue culture fluid. It was then passed in human embryonic lung fibroblasts and in organ cultures of human embryo trachea. This material was not apparently contaminated with bacteria or other viruses and was inoculated into volunteers, in whom it was passed further. For the inoculation of volunteers organ culture fluids or nasal washings were diluted 1 in 10 in saline and 0.5 ml. was dropped into each nostril.Tissue Cultures.-Locally propagated strains of human embryo lung fibroblasts were used. They were cultivated by the methods of Hayflick and Moorhead (1961) six days later. Complete neutralization of the virus was taken as the end-point. It was found essential to use small doses of virus in order to detect antibody, and in tests reported here between 25 and 100 TCD50 were employed. In the serological survey all sera were tested at a dilution of 1 in 10. A number of preparations of 229-E virus fixed complement with volunteers' sera. However, no rising titres were detected in the sera from infected volunteers; it is therefore not certain that the fixation was specific, and consequently the results are not reported here.Volunteers.-These were of both sexes, aged 18 to 50 years, and were cared for in isolation as described elsewhere (Andrewes, 1948;Tyrrell, 1965). Sera were collected before inoculation and two to three weeks later, and nasal washings were collected daily for five days after inoculation. ResultsAs a preliminary to volunteer inoculation we wished to know whether specific antibodies against the virus 229-E were present in the sera of inhabitants of Britain. Accordingly sera collected over the past 10 years from subjects living in various areas were tested at a dilution of 1 in 10 in the neutralization test. As can be seen from Table I, about 30% of sera neutralized the virus.

SUMMARYSix coronaviruses isolated in the U.S.A. have been inoculated into volunteers and all produced colds. Between 10 and 20 % of infected volunteers developed heterologous antibody responses after these and other experimental infections with coronaviruses. The haemagglutination-inhibition test with the OC43 virus strain was found to detect antibody rises after infection with a variety of strains.Studies on normal adult sera taken between 1965 and 1970 revealed a high frequency of neutralizing antibody to one strain (229E) and a frequency of HI antibody to strain OC43 which fluctuated from year to year. Complement-fixing antibodies to these two viruses were also found, revealing an apparent increase in the activity of coronaviruses in the general population of the U.K., during the winter of 1968-9.

SummarySeveral serological interrelationships between various members of the coronavirus group have been revealed in neutralization, complement fixation, and geldiffusion tests, using human and hyperimmune animal sera. Several members of this group of human and animal pathogens are shown to cross-react in one or more type of test, but one member, avian infectious bronchitis virus, was shown to be unrelated. Mouse hepatitis virus (MHVs) was found to be antigenieally related to a number of human types of coronavirus. Difficulties were encountered in the investigation of paired human sera in demonstrating the specificity of antibody rises, placing doubt on the values of some serological studies. The significance of these interrelationships is discussed in the light of other investigations.

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