Rapid baculovirus titration assay based on viable cell side scatter (SSC).

The baculovirus expression system is one of the most powerful tools for the production of recombinant proteins on both laboratory and industrial scales. Multiplicity of infection (MOI) is the crucial parameter for efficient protein expression. To obtain an optimal MOI, it is important to determine titer of virus stock before protein production. Herein, we established a label-free, simple and rapid method for virus titration based on viable cell side scatter (SSC). Generally, the SSC of cells infected with a series of virus dilutions was measured by a flow cytometer at 48 h post-infection, and the probability of infected cells at a given dilution was estimated. For each well with the infection probabilities between 0.20 and 0.80, the range of dilutions was chosen, and virus titer was determined with a statistical method. Log-scale comparison of the results between the SSC based method and a standard plaque assay showed a good correlation (R(2)=0.9853), suggesting the fine accuracy of this proposed method.