Papillomaviruses (PV) are double stranded (
ds) DNA viruses that infect epithelial cells within the skin or mucosa, most often causing
benign neoplasms that spontaneously regress. The immune system plays a key role in the defense against PVs. Since these viruses infect keratinocytes, we wanted to investigate the role of the keratinocyte in initiating an immune response to canine papillomavirus-2 (CPV-2) in the dog. Keratinocytes express a variety of
pattern recognition receptors (PRR) to distinguish different cutaneous pathogens and initiate an immune response. We examined the
mRNA expression patterns for several recently described cytosolic
nucleic acid sensing
PRRs in canine monolayer keratinocyte cultures using quantitative reverse transcription-polymerase chain reaction. Unstimulated normal cells were found to express
mRNA for
melanoma differentiation associated gene 5 (MDA5),
retinoic acid-inducible gene I (RIG-I),
DNA-dependent activation of
interferon regulatory factors,
leucine rich repeat flightless interacting
protein 1, and
interferon inducible gene 16 (IFI16), as well as their adaptor molecules myeloid differentiation primary response gene 88,
interferon-β promoter stimulator 1, and endoplasmic reticulum-resident transmembrane
protein stimulator of
interferon genes. When stimulated with synthetic dsDNA [
poly(dA:dT)] or dsRNA [
poly(I:C)], keratinocytes responded with increased
mRNA expression levels for
interleukin-6,
tumor necrosis factor-α,
interferon-β, RIG-I, IFI16, and MDA5. There was no detectable increase in
mRNA expression, however, in keratinocytes infected with CPV-2. Furthermore, CPV-2-infected keratinocytes stimulated with
poly(dA:dT) and
poly(I:C) showed similar
mRNA expression levels for these gene products when compared with expression levels in uninfected cells. These results suggest that although canine keratinocytes contain functional
PRRs that can recognize and respond to dsDNA and dsRNA
ligands, they do not appear to recognize or initiate a similar response to CPV-2.