ANTIGENIC PROPERTIES 101 



3. Neutralization of Phage Infectivity 



When a phage preparation is mixed with homologous anti- 

 serum there is a progressive decrease in the number of plaque- 

 forming particles. The inactivation process can be interrupted 

 at any time by diluting the phage-antibody mixture below the 

 antibody concentration at which collisions between the reactants 

 occur at a significant rate. Following this dilution there is, 

 in general, no detectable reversal of the inactivation process; 

 the titer of surviving phage does not increase. Apparently, 

 dissociation of the phage-antibody complex does not occur at a 

 measurable rate (Burnet, Keogh, and Lush, 1937; Hershey, 

 1943; see, however, Andrewes and Elford, 1933b; Jerne and 

 Avegno, 1956). Attempts to facilitate dissociation by the addi- 

 tion of formalin-inactivated phage to bind the antibody were 

 unsuccessful (Hershey, 1943). The addition of soluble phage 

 antigen, however, appeared to have a slight reactivating effect 

 (Burnet, 1933b). Although in most instances antibody does 

 not appear to dissociate from the phage particles spontaneously, 

 there is evidence that it can be removed by certain methods. 

 Kalmanson and Bronfenbrenner (1943) found that neutralized 

 phage could be completely reactivated by digestion of the anti- 

 body with papain providing the antibody had not been too 

 concentrated or the serum treatment too prolonged. Appar- 

 ently, if a sufficiently large number of antibody molecules had 

 reacted with the phage particle, the inactivation became irre- 

 versible. Anderson and Doermann (1952b) succeeded in ob- 

 taining more than a 30-fold increase in titer of a neutralized 

 preparation of phage T3 by subjecting it to sonic vibration. 



In the cited reactivation experiments with papain and sonic 

 vibration the concentration of phage during preliminary treat- 

 ment with antiserum was sufficiently high in most instances as 

 to admit the possibility that part, at least, of the plaque-count 

 decrease was due to specific aggregation. It is not certain, 

 therefore, to what extent the observed reactivation can be 

 ascribed to reversal of neutralization, as opposed to disaggrega- 

 tion of virus clumps. However, Hershey (1943) found that 



