THY1 and infection: In contrast, with a high m.o.i (4, based on titration in MRC-5 cells) 10-fold more soluble protein was required to block >90% of the infectivity (during entry over 60 min with acid inactivation), and soluble THY-1 blocked infection less efficiently for the virus that enters with slower kinetics (75% reduction in infectivity without acid inactivation, S6 Fig).