HEMAGGLUTINATION BY ANIMAL VIRUSES 37 



As with the action between virus or KDE and red cells, so with mucoid 

 inhibitor a clear receptor gradient can be established (Stone, 1949c). An 

 inhibitor treated by an active virus will no longer inhibit the indicator virus 

 of the same strain, but will inhibit indicator viruses further down the gradient. 

 This effect can be duplicated by partial treatment with RDE. 



Most mucoid inhibitors are active against all indicator viruses but a few 

 have a more restricted range. For example, bovine submaxillary gland 

 mucoid inhibits only indicator PR8 and strain 1233 (Curtain and Pye, 1955). 

 Sheep salivary mucoid does not inhibit indicator MEL. 



Certain mucoid inhibitors inhibit hemagglutinin of both indicator and 

 active virus. One example is the urinary mucoprotein, which inhibits active 

 MEL and WSE (Burnet, 1952c). Treatment of mucoid inhibitors with potas- 

 sium periodate will destroy inhibiting power but at lower concentrations 

 treatment results in an increased capacity to inhibit hemagglutination by 

 active viruses. Examples are given by Burnet (1948a, 1949b). 



Burnet (1952a) has suggested the generalization that, whenever an in- 

 hibitor is effective against hemagglutination by indicator virus of the same 

 strain, the active virus will destroy the inhibitory action in typical enzymatic 

 fashion. When active virus hemagglutination is also inhibited, it is usual to 

 find little or no enzymatic action. 



For purposes of discussion, we have assumed a clear distinction between 

 Chu inhibitor and mucoid inhibitor. McCrea (1948), however, has surmised 

 that the Chu inhibitor, which is probably a globulin, and the mucoid inhibitor 

 are united in solution. It may not be necessary to go as far as Smith and 

 Westwood (1950) in suggesting that there are not distinct qualitative 

 differences between inhibitors of heated and unheated virus. 



4. Other Types of Inhibitor of Hemagglutination 



Ginsberg et al. (1948) have described the inhibition of mumps hemag- 

 glutinin by the polysaccharide of Friedlander bacillus type B, which will 

 also inhibit mumps infectivity in the egg. This inhibitor acts on the host cell, 

 probably not on the virus, and there is no indication that it is in the class of 

 compounds acted on by RDE. Similarly, the apple pectin and other sub- 

 stances of Green and Woolley (1947) and Woolley (1949) are probably not 

 related to red cell receptor material. We assume the polysaccharide of 

 Klebsiella aerogenes and K. cloacae also belong outside the virus substrate 

 class (Macpherson et al., 1953), together with the pneumococcal filtrate 

 substance of Svec and Forster (1947). 



G. Mechanism of Hemagglutination 



It is a reasonable assumption that hemagglutination is due to the mechani- 

 cal bridging of two or more red cells by virus particles which simultaneously 



