Molluscum contagiosum virus (MCV) is a common, human poxvirus that causes small 
papular skin lesions that persist for long periods without signs of 
inflammation. Previous studies revealed that MCV encodes a family of proteins 
with homology to mammalian IL-18 binding proteins. IL-18 is a proinflammatory 
cytokine that induces synthesis of interferon gamma, activates NK cells, and is 
required for a T-lymphocyte helper type 1 response. We expressed and purified 
the proteins encoded by the MC53L and MC54L genes of MCV, as well as their human 
and murine homologs. All four recombinant proteins were able to bind with high 
affinity to human and murine IL-18 molecules and inhibited IL-18 mediated 
interferon gamma production in a dose-dependent manner. The pirating of IL-18 
binding proteins by poxviruses and their use as decoy receptors is consistent 
with the critical role of IL-18 in defense against virus infections and provides 
a mechanism for evasion of the immune system by MCV.