InVitro Studies oftheAntirhinovirus Activity ofSoluble Intercellular Adhesion Molecule-1

We studied theinvitro antirhinovirus activity ofa soluble formofintercellular adhesion molecule-i (sICAM-1). sICAM-1 inhibited thecytopathic effect of10representative humanrhinovirus (HRV)serotypes of themajorreceptor groupwith, 50%oeffective concentrations (ECs.s) of0.1to7.9,ug/ml. Celltype-dependent variation intheinhibitory activity ofsICAM-1 was observed fortwomajorreceptor group serotypes inHeLa cells (EC50, >32,ug/ml), andno inhibitory effect was observed fortwoserotypes which use different cell receptors. Yield reduction assaysshowed that sICAM-1 inhibited thereplication ofHRV serotype 39(HRV-39) inhumanadenoid explants ina concentration-dependent manner. Nodirect inactivation ofinfectivity of HRV-39(EC50, 0.5jLg/ml) was observed after incubation withsICAM-1(32jg/mi) forup to24h.Singlecycle-of-replication experiments withtheaddition ofsICAM-1 at10pg/mI atdifferent times showed that the inhibitory effect occursonlywhensICAM-1 isaddedwithin 30minafter infection. Inexperiments inwhich absorption was carried outat4°Candthen a single cycle ofreplication incubation was carried outat33°C, it was found thatsICAM-1 at10jig/ml was inhibitory onlywhenitwas present during theabsorption period. Ourdatashowthat sICAM-1isinhibitory forrepresentative majorreceptor groupserotypes ofHRV intwo cell lines andhumanrespiratory epithelium, that theinteraction ofsICAM-1 withHRVisreadily reversible by dilution, andthattheinhibitory effect ofsICAM-1 on virusreplication ispresent early intheinfection cycle. Theglycoprotein intercellular adhesion molecule type1 (ICAM-1) hasbeenidentified as thecell receptor forthe major receptor groupofhumanrhinoviruses (HRVs), which includes approximately 90%ofthenumbered serotypes (7, 14,15). ICAM-1, whichisamemberoftheimmunoglobulin superfamily, isacell surface molecule whichfunctions asa ligand forthelymphocyte function-associated antigen-1 and promotesinteractions between leukocytes anda numberof celltypes(9). ICAM-1iscomposed offiveextracellular immunoglobulinlike domains, one transmembrane anchor, andan intracytoplasmic C-terminal domain(7,14).The primary site fortheinteraction ofbothlymphocyte functionassociated antigen-1 andHRV seems tobewithin domain1 ofICAM-1(13). Soluble formsofICAM-1(sICAM-1) have beenexpressed inChinese hamster ovary(CHO)cells and havebeenshowntoinhibit thecytopathic effect (CPE) caused byHRVsandother picornaviruses that useICAM-1 as a cellreceptor (8,10).Inone study(10), sICAM-1 concentrations ofapproximately 1,g/ml(approximately 18 nM)inhibited theCPE ofHRV serotype 54(HRV-54) by 50%(50%inhibitory concentration), and10p,g/ml inhibited theCPEbymore than90%.Whenbinding ofradiolabeled HRV-14toHeLacells was measured, concentrations of50 ,ug/ml (approximately 0.9,uM)were necessarytoinhibit binding by50%(10). Anotherstudy (8)foundthat0.4p,M sICAM-1inhibited HRV-3infectivity by50%andthat concentrations ofabout3,uMcaused 50%inhibition ofradiolabeled HRV-3binding toICAM-1immobilized on microtiter dishes. Herewe reporttheresults ofinvitro studies conducted toassessfurther theantirhinovirus activity ofsICAM-1forrepresentative major receptor groupserotypes of