HEMAGGLUTINATION BY ANIMAL VIRUSES 33 



Although full treatment by RDE removes all receptors from red cells, it is 

 possible to halt the action at any stage by the addition of calcium deionizing 

 agents and so to duplicate the action of any myxovirus strain in producing 

 cells at the corresponding place in the gradient. The gradient so produced 

 corresponds to that produced by viruses, with one exception; the mumps virus 

 receptor falls later in the RDE gradient (Burnet et al., 1946). With horse or 

 ox cells the mumps receptor remains intact, even when all influenza receptors 

 have been destroyed (Stone, 1947). 



Electrophoretic mobility of guinea pig cells acted upon by RDE in vivo fell 

 from 1.10 to 0.20 /x/sec. /volt/cm., which is a lower figure than produced by 

 any influenza virus (French and Ada, 1954). The electrophoretic mobility of 

 human cells fully treated in vitro by RDE falls from 1.30 to 0.17 /x/sec./volt/ 

 cm. (Ada and Stone, 1950). 



RDE-treated cells develop T agglutinogens, and we have discussed above 

 the development of other new surface antigens. 



It is evident that RDE duplicates the action of the virus enzyme but takes 

 the reaction further than any known myxovirus. As might therefore be 

 expected, RDE will remove agglutinating virus from red cells more rapidly 

 than the virus itself would normally elute, and will also remove indicator 

 viruses. 



b. Periodate-Virus-RDE (PVR) Cells. Fazekas de St. Groth (1949) showed 

 that treatment of fowl or human red cells with amounts of potassium period- 

 ate (KI0 4 ) in the range 0.2 to 2.0 mg. KI0 4 per gram of cells produced a modi- 

 fication of cell receptors, rendering them insusceptible to destruction by 

 virus enzyme and hence preventing elution of adsorbed virus. If, after ad- 

 sorption of virus with agglutination, the cells are treated with RDE, receptors 

 unoccupied by virus are destroyed so that the cells are stabilized but carry 

 firmly attached virus particles. Such PVR cells have properties analogous to 

 normal cells on which NDV or mumps virus is irreversibly bound. 



E. Indicator Virus 



Francis (1947) found that if influenza B virus LEE was heated to 56°C, 

 its hemagglutinating activity remained almost intact, but the heated virus 

 was not only more sensitive to the hemagglutinin-inhibiting action of im- 

 mune serum than active virus but was also inhibited by normal serum. This 

 action of normal serum was subsequently shown by Anderson (1948) and 

 McCrea (1948) to be due to a mucoid inhibitor. The change in the virus 

 following such mild heat treatment is usually referred to as conversion to 

 indicator virus. Stone (1949b) used the term because viruses in this state 

 indicate the presence of inhibitory mucoids in various animal fluids and 

 extracts and can be used to titrate them. 



vol. in. — 3 



