ADSORPTION OF PHAGE TO HOST CELL 155 



the fact that the host cells became agglutinable by antiphage 

 serum. PI A did not prevent adsorption of phage to host cell 

 but did interfere with the next step in the infectious process. As 

 we have seen in Chapter VIII phage particles treated with anti- 

 phage serum are also able to adsorb to the host cell ahhough they 

 are noninfectious. Burnet and Freeman concluded from these 

 experiments that phage antibodies and PIA probably do not re- 

 act with the same site on the phage surface but rather at adjacent 

 sites. 



The interaction of phage, PIA, antiphage serum, and host eel) 

 is discussed further by Burnet, Keogh, and Lush (1937) : 



The first stage in the lysis of susceptible bacteria requires tiie mutual specific 

 union of certain elements of complementary molecular configuration on the 

 surfaces of the phage particle and bacterium respectively. The specific ele- 

 ment on the bacterial surface is intimately related to the polysaccharide hapten 

 which determines the antigenic character of the bacterium. The hapten, as 

 finally isolated by chemical methods, is not present as such in the living bac- 

 terial surface, but forms an essential part of a more complex molecular pattern. 

 It is to certain aspects of this pattern, not necessarily the same for each phage 

 lysing the organism, that specific phage adsorption occurs. 



Any process by which the bacterial surface components are 

 brought into solution necessarily destroys to some extent their 

 specific molecular pattern. The fact that reaction of phage 

 with its antibody makes the phage resistant to inactivation by 

 PIA must mean that neutralizing antibody and PIA react with 

 receptors that are spatially contiguous and parts of a single com- 

 plex. These detailed suggestions have been shown by later 

 work to be remarkably accurate. 



The kinetic experiments of Burnet were confirmed by Ellis 

 and Spizizen (1941) using coliphage PI. The inactivation by 

 PIA was markedly influenced by salt concentration, being opti- 

 mal at 0.5 per cent NaCl and negligible in 25 per cent NaCl or 

 in the absence of salt. Phage inactivated by PIA could not be 

 reactivated by changing the salt concentration. About 5 per 

 cent of the phage population was very resistant to inactivation. 



