How are virus titers determined?
There are 3 commonly used protocols for determining adenovirus titer: (1) OD260 Assay, (2) Plaque Formation Assay, and (3) End-point Dilution Assay. OD260 assay measures the concentration of viral DNA and protein. It does not distinguish between intact, infectious viruses and damaged, non-infectious viruses. It is a physical assay measuring the concentration of total viruses, live and dead. Based on OD260, the concentration of viral particles (VP) could be obtained. To measure the OD260, the virus stock has to be purified first. On the other hand, plaque formation assay measures the concentration of infectious viruses, and therefore it is a biological assay. Basically, a mono-layer of HEK293 cells are infected with a series of virus dilutions. Viruses will propagate in infected cells, and eventually cause cytotoxicity effects in that cell, and get released. The released viruses will infect neighboring cells, and the whole process will be repeated, eventually leading to the formation of
