Properties of Pneumonia Virus of Mice (Pvm) in Relation to Its State

Abstract

In a previous communication (1) evidence was presented which indicated that the hemagglutination observed with heated suspensions of lungs infected with pneumonia virus of mice (PVM) was caused by the virus itself, even though the virus had been rendered non-infectious in the course of heating. From the available data it was concluded that the virus has the capacity to combine firmly not only with mouse or hamster erythrocytes but also with lung tissue particles from certain host species, and that appropriate heating serves to release the virus from combination. The occurrence of such combination with PVM appeared to account for its capacity to cause hemagglutination and for other unusual attributes of this virus.It is the purpose of this paper to present additional evidence in support of the conclusion (1) that combination between PVM and tissue particles does occur, and to elucidate further the mechanism and significance of this phenomenon. I t will be shown that the virus can be released from combination by treatment with alkali. Further evidence will be presented to demonstrate that PVM, as it exists in vivo, is not combined and that combination occurs in the process of grinding tissues infected with it. Moreover, it will be shown that free infectious virus recovered by a technique described in the preceding paper (2) is not combined and that estimates of its titer can be made directly both in vivo and in vitro. It will be shown that in demonstrating the presence of PVM or in estimating its titer the results obtained by in vitro techniques are more accurate than corresponding results obtained in vivo. Finally, evidence will be presented indicating that the virus may occur in several different states and that it possesses certain distinguishing properties in each.

THE ASSOCIATIVE REACTIONS OF PNEUMONIA VIRUS OF MICE (PVM) AND INFLUENZA VIRUSES: THE EFFECTS OF pH AND ELECTROLYTES UPON VIRUS-HOST CELL COMBINATIONS

“…It was found that the dissociated PVM preparation employed, which had a hemagglutination titer of 10 -8"1, had an M.S.50 virus titration end point of 10j 2.2. The latter figure is comparable to the infectivity titers obtained previously with free infectious virus of similar hemagglutination titer (5). It is evident that following dissociation in the presence of dextrose PVM retained the property of infectivity.…”

“…shown that, although PVM cannot be demonstrated by the hemagglutination technique in suspensions of infected mouse lungs unless they are subjected to treatment which releases the virus from combination with tissue particles (1)(2)(3)(4)(5), the virus can be so demonstrated with slices of unground lungs (5) as well as in tracheal washings from infected lungs (4). This indicates that in the intact infected lung some virus is present in an uncombined state, and that combination between free PVM and lung particles occurs when the lungs are ground.…”

“…Infectivity of Dissociated PVM.--Either heat or alkali treatment, procedures used previously to release PVM from combination in infected lung suspensions, renders the virus non-infectious (1)(2)(3)(4)(5). On the other hand, free infectious PVM, prepared by extracting unground lung slices with cold saline, has been shown to be infective (5). It was important to determine if dissociated virus preparations also were infectious.…”

“…In order not to cause inactivation of the very unstable property of infectivity, the dextrose solution was buffered at pH 7.2 with 0.01 ~ phosphate, and centrifugation was carried out at 4°C. The supernate was diluted in cold buffered dextrose and the virus fitered in mice as described elsewhere (5).…”

Studies on Pneumonia Virus of Mice (Pvm) in Cell Culture

“…That PV-M produced by BHK21 cells can combine with a component of mouse lung was demonstrated by mixing the virus with mouse lung homogenate and assaying for hemagglutinin (Table IV). These results indicate that PVM grown in cell culture is not combined with a cellular inhibitor that prevents hemagglutination, and thus is similar to the free virus Curnen and Horsfall obtained by carefully perfusing the infected mouse lung (11,38).…”