FIG 1.

Astrovirus binding and entry into Caco-2 cells. (A) Trypsin-treated HAstV-8 (at an MOI of 0.1) was added to Caco-2 cells and incubated at 4°C for the indicated times to allow virus attachment, but not entry. The unbound virus was removed, the cells were washed twice, and the infection was allowed to proceed for 16 h at 37°C. Finally, the cells were fixed and immunostained as described in Materials and Methods. The input virus (V₀) was considered to be that determined by infecting the cells for 1 h at 37°C, while the unbound virus (V_t, calculated as the total virus added minus the number of infected cells) was considered the difference of the input and the bound virus detected at a given time. (B) Two-fold dilutions of NR-labeled HAstV-8 were adsorbed to Caco-2 cells for 1 h at 4°C in the dark and then shifted to 37°C and exposed to white light at the indicated time points. The titer obtained in each case is expressed as a percentage of the infectivity obtained with the NR-HAstV kept in darkness. The arithmetic means ± standard deviations of three independent experiments performed in duplicate are shown. The dashed line indicates the time at which 50% of HAstV infectivity was no longer affected by white light.