FIG. 6.

Protease treatment of ocular cells inhibits binding of CVA24v virions to NHC and HCE cells. Cells (2 × 10⁵) in suspension were pretreated with bromelain and ficin proteases (which cleave at cysteine residues) or V8 protease (which cleaves at glutamic acid or aspartic acid residues), prior to incubation with 5,000 ³⁵S-labeled CVA24v virions/cell. Cell-associated radioactivity (CPM [counts per minute] bound) was determined by using a scintillation counter. Cell viability was assessed with the trypan blue method immediately after proteolytic digestion and no cytotoxic effects mediated by the protease treatment could be seen, compared to untreated control cells. The results are presented as means ± standard deviations of duplicate samples from at least three independent experiments.