Interferon-induced gene expression in cervical mucosa during human papillomavirus infection

The aim of this study is to monitor type I interferon (IFN) activation in the cervical mucosa of Human Papillomavirus (HPV)-infected and uninfected women attending a routine gynaecologic clinic. The expression of three IFN-induced genes (MxA coding for human Mixovirus resistance protein A, ISG15 Interferon Stimulated Gene coding for a 15 kDa ubiquitin-like protein and UBP43 coding for the ISG15 isopeptidase) was determined as the mRNA copy number in cervical cells, normalized to the mRNA ones of the beta-glucuronidase gene. Type-specific HPV-DNA load was concurrently determined in the HPV-positive samples. Out of 127 samples tested, 54 were sufficient for both DNA and RNA extraction. The type-specific HPV-DNA copy numbers in the 34 HPV-positive samples varied widely. No significant association was found between copy numbers of MxA, ISG15, UBP43 and HPV status or viral load. However, despite a marked inter-individual variability, ISG15 expression was significantly higher when low-risk HPV infections were compared with HPV-negative samples, while high-risk HPV infections had very low ISG15 levels. The lack of ISG15 activation in high-risk HPV-infected cervical cells could be due to the lack of p53-mediated induction or to HPV-directed specific inhibition of type I IFN pathways. This study approach might be of value in clarifying the role of type I IFN activation in determining the clearance or persistence of HPV infections.