Hemagglutination Induced by Viruses *

Since the original demonstration of the hemagglutination induced by influenza virus,, 118 a number of other important viruses have been reported as causing the agglutination of chicken erythrocytes. Specific agglutination of these red blood cells has been observed with vaccinia virus,21 the virus of Newcastle disease,1 that of fowl plague,17 variola virus,22 and mumps virus.'6 It has also been shown that mouse pneumonitis virus will produce the agglutination of mouse and hamster erythrocytes, but not those of the chicken.20 With all of the above-mentioned viruses the agglutination olf the red cells may be inhibited by the addition of the specific immune serum. Hirst"3 observed that chicken erythrocytes to which influenza virus was adsorbed and from which it was subsequently eluted were refractory to agglutination by the homologous strain and also by heterologous strains of influenza virus. Both Hirst"4 and Ziegler and Horsfall27 have recognized the fact that the refractory state of the red cells after adsorption and elution of influenza virus may present more than a superficial analogy to the interference phenomenon which has been demonstrated in animals with numerous viruses. The mechanism responsible for hemagglutination is obscure and it is difficult to imagine that it is a true antigen-antibody reaction. Hirst13 suggests that the reaction is mediated by an enzyme contained in the red blood cell. According to this theory, it might well be possible to isolate the enzyme or recept-or substance responsible for the agglutination. Burnet2 postulates the existence on the red cell surface of multiple receptors whose degree of attachment to the cell is graded from loose to firm. The loosely attached. receptors are available to any of the viruses capable of causing hemagglutination, but the more firmly bound are accessible only to ttie more active viruses.