A captured viral interleukin 10 gene with cellular exon structure

We have characterized a novel, captured and fully functional viral interleukin (IL)-10 homologue (OvHVIL-10) from the gammaherpesvirus ovine herpesvirus 2. Unlike IL-10 homologues from other gammaherpesviruses, the OvHVIL-10 peptide sequence was highly divergent from that of the host species. The OvHVIL-10 gene is unique amongst virus captured genes in that it has precisely retained the original cellular exon structure, having five exons; of similar sizes to the cellular counterparts. However, the sizes of the introns are dramatically reduced. The OvHVIL-10 protein was shown to be a non-glycosylated, secreted protein of M-r 21 000 with a signal peptidase cleavage site between amino acids 26 and 27 of the nascent peptide. Functional assays showed that OvHVIL-10, in a similar way to ovine IL-10, stimulated mast cell proliferation and inhibited macrophage inflammatory chemokine production. This is the first example of a captured herpesvirus gene retaining the full cellular gene structure.