Printed in Great Britain Influence of Type and Concentration of Sera in vitro on Susceptibility of Genetically Resistant Cells to Mouse Hepatitis Virus

The type and concentration of sera used to support macrophages was found to influence the in vitro destruction of macrophages from genetically resistant C3H mice by the VRINCETON strain of mouse hepatitis virus, and the accompany-ing conversion of mouse hepatitis virus (PRINCETON) to the variant virus, mouse hepatitis virus (C3H). Cells incubated in 2o ~ horse serum were more susceptible to destruction than those in 9o ~ horse serum. Susceptibility was greatest in the presence of IO ~ foetal calf serum, while cells in IO ~ mouse sera were the most resistant. Differences in susceptibility were as great as io,ooo TCD 5o. The sera had no direct effect upon either mouse hepatitis virus (PRINCETON) inoculum virus or the released variant virus, but appeared to influence intracellular adapta-tion of virus. In plaque titrations using reduced concentration of horse sera, mouse heptatitis virus (VRINCETON) produced small plaques on C3H cells. The variant virus, mouse hepatitis virus (C3H), produced both large plaques character-istic of mouse hepatitis virus (C3H) and small plaques characteristic ofmouse hepa-titis virus (PRINCETON). The results suggest hat a fraction of mouse hepatitis virus (VRINCETON) virus multiplies in resistant C3 H cells, and is then converted to mouse hepatitis virus (C3H), and that mouse hepatitis virus (PRINCETON) continues to be carried in stocks of mouse hepatitis virus (C3H) during passage in C3H cells. The outcome of infection of genetically resistant C3H macrophages with mouse hepatitis virus (PRINCETON) was greatly influenced by the type and concentration of sera used to support macrophages