We identified a viral IL-10 homolog encoded by an ORF (UL111a) within the h
uman cytomegalovirus (CMV) genome, which we designated cmvlL-10, cmvlL-10 c
an bind to the human IL-10 receptor and can compete with human IL-10 for bi
nding sites, despite the fact that these two proteins are only 27% identica
l. cmvlL-10 requires both subunits of the IL-10 receptor complex to induce
signal transduction events and biological activities. The structure of the
cmvlL-10 gene is unique by itself. The gene retained two of four introns of
the IL-10 gene, but the length of the introns was reduced. We demonstrated
that cmvlL-10 is expressed in CMV-infected cells. Thus, expression of cmvl
L-10 extends the range of counter measures developed by CMV to circumvent d
etection and destruction by the host immune system.