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XC plaque; mink S+L- focus; feline S+L- focus; mink cell focus

BioReliance offers two types of infectivity assays for detection of retroviruses. In the focus formation assay, the indicator cell line, which carries multiple copies of a sarcoma gene, forms foci of infected cells that can be detected microscopically and counted. In the XC plaque assay, the indicator cells (XC) form large syncytia, which resemble plaques. One type is used for detecting retrovirus in vaccine or cell-free culture supernatant collected from the test cell line. The second type uses the test cells directly in the cocultivation assays.