THE MORPHOLOGICAL APPROACH 83 



VIII. Myxoviruses 



A. Introduction 



The influenza, Newcastle, mumps and fowl plague viruses have been 

 recently classified together because of morphological and biochemical simi- 

 larities ( Andre wes et al., 1955). 



As with other animal viruses, very little is known about the penetration 

 of these viruses into cells. Although phagocytosis may occur even in ciliated 

 cells (Ropes, 1930), it may only be presumed that virus may gain entrance to 

 the cell by this means. The consistently active pinocytosis in chicken macro- 

 phages was used to follow the entrance of Newcastle disease virus into these 

 cells (Hotz and Bang, 1957b), but no details of the process were apparent in 

 the electron microscope sections other than the presence of virus in the fluid 

 droplets as they were engulfed. Perhaps because of the peculiar filamentous 

 forms (Mosely and Wyckoff, 1946) which occur with some of the members, 

 they have been studied more thoroughly than some of the other animal 

 viruses. Although the generally destructive effect of influenza virus on certain 

 respiratory cells was well known (Stuart-Harris and Francis, 1938; Perrin 

 and Oliphant, 1940; Hers, 1954), no clear picture of the effect of these viruses 

 on the cell was available before electron microscopy showed the more detailed 

 changes present in cells. Recent studies with fluorescent antibody have also 

 been particularly revealing. Phagocytosis of influenza virus by human and 

 mouse leucocytes has been demonstrated by using the fluorescent antibody 

 technique (Boand et al., 1957), but this procedure has not been applied to 

 normally susceptible cells. 



However, as will be brought out in the discussion, the effects of these 

 viruses may well vary with the strain of virus used and with the type of 

 host cell. For this reason we have summarized in Table I the references to 

 appropriate studies. The blank areas represent our lack of knowledge of any 

 pertinent electron microscope studies. It may be seen clearly that although a 

 number of different cell systems and some variation in virulence of the viruses 

 have been studied, a preponderance of work has been done with the cells of 

 the allantoic sac and relatively little with the cells which are most involved 

 in the natural diseases. 



Although it is possible to see influenza virus filaments by dark field micro- 

 scopy (Chu et al., 1949), and to stain them (Lindemann, 1957), the problem of 

 their formation has incited a maximum of effort by electron microscopists. 

 It seems clear that the clue lies in the surface activity of the cell, but the 

 very superficial nature of this activity may hide the deeper problem 

 of how the virus itself formed. This has been made particularly clear by 

 the studies on the nuclear localization of antigen by fluorescent antibody 

 technique. 



