title: Cystatin D, a natural salivary cysteine protease inhibitor, inhibits coronavirus replication at its physiologic concentration.
abstract: This study was conducted to examine the effect of cystatin D, a newly discovered salivary cysteine protease inhibitor, on human coronavirus replication. When MRC-5, human diploid lung cells, were incubated with dilutions of recombinant human cystatin D from 0.65-10 microM for 1 h prior to, during and after infection with coronavirus OC43 and 229e strains, a decrease in virus yield was observed resulting in an IC50 of 0.8 microM for both virus strains. This dose is within the normal concentration range of cystatin D, 0.12-1.9 microM found in saliva. When a single dose, 2.5 microM, was applied, cystatin inhibition of release of virus progeny was not overcome until three days post infection whereas inhibition by leupeptin, a serine and cysteine protease inhibitor, was completely abrogated by two days. When cellular toxicity was measured by 3H-thymidine uptake, cystatin D did not markedly affect cell proliferation below a 10 microM dose. The results demonstrate that cystatin D is a potent inhibitor of coronavirus replication.
authors.affiliation: Department of Microbiology, State University of New York at Buffalo 14214, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Collins
authors.forename: A
authors.initials: A
authors.lastname: Grubb
mesh_terms: D017934:Coronavirus / Q000187:drug effects* / Q000502:physiology; D028941:Coronavirus 229E, Human; D028962:Coronavirus OC43, Human; D015891:Cystatins / Q000494:pharmacology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D006801:Humans; D011994:Recombinant Proteins / Q000494:pharmacology; D012463:Saliva / Q000276:immunology*; D013997:Time Factors; D014776:Virus Cultivation / Q000379:methods; D014779:Virus Replication / Q000187:drug effects*
chemical_list: D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D011994:Recombinant Proteins; C071378:CST5 protein, human