Fig. 1.

Fcwf-4 Cornell University (CU) cells produce high titers of cell-free type I FIPV with rapid growth kinetics. A) Virus growth kinetics measured from cell-free supernatants of AK-D (black), Fcwf-4 ATCC (blue), and Fcwf-4 CU (red) cells infected with FIPV Black (MOI=0.1) over 96 h. Arrows indicate time of peak titer presented as plaque-forming units (pfu)/mL. Titer determined by plaque assay on AK-D cells in triplicate; error bars ± SD. B) Cell-associated and cell-free virus titers were determined following infection of Fcwf-4 CU, AK-D, and Fcwf-4 ATCC cells with FIPV Black (MOI=0.1). Cell-free titer was determined from cell-clarified supernatants; cell-associated titer was determined from suspended cell monolayers following three freeze-thaw cycles alternating between −80 °C and 37 ^oC. Samples were taken at hours post-infection (hpi) just prior to, at, and following the maximum (max) virus titer for each cell type. Titers determined by plaque assay on AK-D cells in triplicate; error bars ± SD.