22 S. G. ANDERSON 



Hemagglutinating viruses can be conveniently described in three groups: 



1. The myxovirus group, in which the virus particle itself is the hemagglut- 

 inating agent and also carries an enzyme (neuraminidase) which allows 

 elution of virus with destruction of red cell receptors. 



2. Viruses in which the virus particle is believed to be the hemagglutinin 

 but which possess no eluting enzyme and produce no destruction of cell 

 receptors on elution. This group includes most of the arthropod-borne 

 viruses, the encephalomyocarditis (EMC) viruses, one member (GD VII) of 

 the polio virus group, and pneumonia virus of mice. 



3. Viruses which, during growth in suitable cells, produce a hemag- 

 glutinin which is separate from the virus particle. This includes some of the 

 poxvirus group and some strains of psittacosis and related viruses. 



I. The Myxovirus Group 

 A. Historical 



Hirst (1941) and McClelland and Hare (1941) independently reported that 

 chick red cells were agglutinated by fluids from chick embryos infected with 

 various strains of influenza virus. Hirst (1942a,b) explored the new field 

 extensively, providing a soimd basis for all subsequent work on the pheno- 

 menon. He showed: (1) that the hemagglutinin was identical with the infec- 

 tive particle, but (2) that, under the action of such agents as heat and 

 formalin, infectivity could be destroyed with retention of hemagglutinating 

 power, (3) that the spontaneous elution of hemagglutinin with stabilization 

 of the red cell suspension closely resembled an enzymatic reaction, and (4) 

 that hemagglutination could be inhibited by specific antibody and, to a less 

 and variable extent, by some normal sera. 



It was subsequently shown by Burnet (1942) that Newcastle disease virus 

 (NDV) agglutinated red cells in similar fashion. Fowl plague virus was shown 

 to be active by Lush (1943) and mumps virus by Levens and Enders (1945). 

 The common property of these viruses to agglutinate red cells by adsorbing 

 to mucinlike material on the cell surface was used to define the group 

 myxovirus and to provide its name (Andrewes et ah, 1955). 



B. Hemagglutination 



1. Relation to the Virus Particles 



Hemagglutination by standard infective preparations of influenza virus is 

 due to adsorption of virus particles on the red cell surface; most workers 

 picture the process as virtually a simple bridging between cells by the virus 

 particles, with a resultant building-up of aggregates of cells. In addition to 

 the virus particle hemagglutinin, a hemagglutinin associated with a still 



