Shrimp interferon is rather a portion of the mitochondrial F0-ATP synthase than a true α-interferon

Type I interferon (IFN) is a multimember cytokine family commonly known by its involvement in antiviral defense. Recently (2005), an interferon-like protein (IntlP) homologue to mammalian IFN-α was identified for the first time in crustaceans, in the shrimp Penaeus (Marsupenaeus) japonicus. IntlP was expressed only in WSSV-resistant shrimps (but not in naïve shrimps) and was capable to induce an unspecific antiviral effect on infected fish cells. In the present paper we show that IntlP is in reality a portion of the mitochondrial F0-ATP synthase (60–73% identity with insect F0-ATP synthase β-chain) and not a homologue of mammalian type I interferon. In our hands, sequences corresponding to IntlP/F0-ATP synthase β-chain were equally amplified in naïve and WSSV-infected Litopenaeus vannamei and also in two wild Brazilian shrimp species. From the obtained results we assumed that type I IFN homologues have not yet been demonstrated in any shrimp or crustacean.