APPENDIX 465 



Use of K Value of Antiserum to Demonstrate Serologic Relatedness 

 among Phages 



If 2 viruses are serologically related, an antiserum against 1 

 of them will neutralize the infectivity of both. In all cases 

 studied so far, the rate of neutralization has been greater with 

 homologous virus and antiserum than with heterologous sys- 

 tems. The K value of an antiserum when tested with various 

 viruses can be taken as an indication of the degree of relatedness 

 of the viruses. For instance, the coliphages T2, T4, and T6 

 form a closely related group. An antiserum against T2 had a 

 K value of 200 when measured against T2, a K value of 50 when 

 measured with T4 and of 90 when measured with T6. In con- 

 trast, coliphages T3 and T7 are much less similar serologically. 

 A T3 antiserum with a A' value of 300 with T3 had a K value 

 of only 1.5 with T7, whereas a T7 antiserum with a K value of 

 1000 with T7 had a A' value of 1 with T3. 



Luria (1945a) used this method to test the relatedness of host 

 range mutants of Tl and T2 to the parent strains and found no 

 detectable difference in A' values for neutralization of parent and 

 mutant whether tested with antiserum against the parent or the 

 mutant. 



With this method Hershey (1946a) attempted to find an 

 antigenic difference between an r type phage mutant and 

 its r+ ancestor, but failed to detect any difference even when 

 the sensitivity of the method was increased by cross-absorption 

 of the sera with the heterologous phage. Nor could he detect 

 any antigenic difference between host range mutants and their 

 ancestors, confirming Luria. Hershey was, however, able to 

 detect significant immunologic differences in various races of 

 T2 which had been subcultured in different laboratories for 

 some time, indicating that antigenic differences in phage do 

 develop, probably by mutation, during repeated subculture. 



This method of antigenic analysis is likely to be useful in a 

 study of the phages released from bacteria simultaneously in- 

 fected with 2 different types of virus, where there is evidence for 



