Richard A. Steeves

B-tropic Friend virus: a host-range pseudotype of spleen focus-forming virus (SFFV).

Abstract The N-tropic strain of Friend virus (FV) complex includes two different infectious entities: defective SFFV and helper virus, the latter of which is responsible for the N-tropism of the complex. The N-tropic helper, highly infectious in homozygous Fv -1 n mice, is poorly infectious in Fv -1 b mice. B/T-L virus, a leukemogenic virus free of SFFV, includes a B-tropic helper virus which is much more infectious in Fv -1 b than in in Fv -1 n mice. N-tropic FV complex to which B/T-L virus has been added (i.e., SFFV with its associated N-tropic helper, plus B-tropic helper) induced FV disease in young Fv -1 b mice and gave rise to a strain of virus which could be passaged serially through Fv -1 b hosts. Analysis of the host range properties of the new virus strain indicated that the N-tropic helper component of FV complex had been rapidly eliminated during the first few passage generations of the virus, leaving a B-tropic pseudotype of SFFV, i.e., SFFV associated with B-tropic helper virus. Susceptibility to this B-tropic pseudotype was influenced in the expected manner by the Fv -1 and Fv -2 genes, but host range studies indicated that one or more previously unidentified genes also influenced the host response to this virus. Serial forced passage of the B-tropic FV through Fv -1 -restrictive hosts resulted in the recovery of an NB-tropic variant of the pseudotype.

A target cell assay for friend virus

Abstract A method has been developed for the in vitro infection and subsequent quantification of murine hemopoietic target cells with FV grown in vivo . The number of infected FV releasing cells is quantified in a spleen colony assay for infectious centers. The hemopoietic nature of these cells is demonstrated by the fact that bleeding increases the number of target cells in spleen and bone marrow of mice. This procedure may be of significance in the study of both FV-target cell interactions and the problem of oncogenic transformation by FV.

Biological activity of Friend spleen focus-forming virus after cold storage☆

Abstract Two stocks of Friend spleen focus-forming virus (SFFV) were prepared, one in saline and the other in Eagles medium with 2% fetal calf serum, and the effects of different freezing, storage and thawing temperatures were determined for the recovery of infectious virus from each diluent. Once frozen, virus maintained its titer at −70 and at −170 °C for up to 13 weeks, while it lost titer at −13 °C more rapidly if it had been prepared in saline than in medium. However, during the freezing process lower ambient temperatures (−70 and −170 °C) gave lower virus yields than a higher temperature (−13 °C) did. Similarly, rapid thawing (in a 37 °C water bath) was less efficient than slow thawing (in 4 or 20 °C air) for the recovery of infectious SFFV, This study illustrates the importance, for efficient recovery of leukemogenic activity from stored murine leukemia virus stocks, of the temperature used for freezing or thawing, as well as for storage.