270 T. FRANCIS, JR. 



another of the viruses. These events have been well confirmed with serum of 

 experimental animals, especially by Price (1956) and by Casals (1957) with 

 hyperimmune mouse sera and hemagglutination-inhibition tests. They 

 correspond to the results observed with groups of influenza virus, leading to 

 the doctrine of "original antigenic sin." A specific response to infection is 

 obtained in an inexperienced host but after previous infection by a member of 

 the group, reinfection elicits hemagglutination-inhibition, complement-fixing, 

 neutralizing antibodies and active immunity of a marked group character. 

 Furthermore, it was observed here, too, that serum from an animal late after 

 inoculation exhibited broader group coverage. 



It can be emphasized that this basis for demonstrating mutual serological 

 relationships is becoming generally applicable to viruses which may appear 

 to be independent multiple variants, as measured by initial serological 

 response. It has not as yet been explored in the complex system of adeno- 

 viruses, Coxsackie, and ECHO viruses, but it seems a fruitful area for study. 

 Skinner (1953) has reported that infection with a second type of cattle 

 immune to one type of foot-and-mouth disease virus results in antibody to 

 the second type, but also sharply enhances antibody to the initial type. 

 Vaccination of human subjects having antibodies to type 2 poliovirus alone 

 with polyvalent poliomyelitis vaccine results in greater antibody rises to 

 types 1 and 3 than occurs in persons without antecedent type 2 antibody; 

 this illustrates a group response (Francis, it at., 1957). 



The results demonstrate that serological variation at apparently high levels 

 of difference within the species still maintains a close relationship with other 

 members of the species. This does not appear to be the result of a single 

 common antigen, but of multiple shared antigens which contribute to sero- 

 logical specificity and commonalty. 



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