Cystatin D, a natural salivary cysteine protease inhibitor, inhibits coronavirus replication at its physiologic concentration

Oral Microbiol Immunol. 1998 Feb;13(1):59-61. doi: 10.1111/j.1399-302x.1998.tb00753.x.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Coronavirus / drug effects*
  • Coronavirus / physiology
  • Coronavirus 229E, Human*
  • Coronavirus OC43, Human*
  • Cystatins / pharmacology*
  • Cysteine Proteinase Inhibitors / pharmacology*
  • Depression, Chemical
  • Dose-Response Relationship, Drug
  • Humans
  • Recombinant Proteins / pharmacology
  • Saliva / immunology*
  • Time Factors
  • Virus Cultivation / methods
  • Virus Replication / drug effects*


  • Cystatins
  • Cysteine Proteinase Inhibitors
  • Recombinant Proteins
  • CST5 protein, human