This study used the rodent Mastomys coucha latently infected with Mastomys natalensis papillomavirus (MnPV) and Mastomys coucha PV2 (McPV2), which induce skin papillomas and anogenital condylomas, respectively, to investigate PV antibody responses as serological markers during pathogenesis. In a case-control study (137 animals), virus and tumour prevalence correlated with the seroresponse against the early E2 and late L1 viral proteins. A prospective study (53 animals) revealed for the first time the course of these antibody responses during all stages of a natural PV infection. Numerous tumour entities were observed on the eyelid and in the oral cavity. DNA analyses indicated that McPV2 was not restricted to condylomas but was also present in these mucosa-associated papillomas. The serological survey using a recently established glutathione S-transferase-capture ELISA detected a strong correlation between MnPV L1-specific antibodies and the presence of papillomas on the skin, eye and ear (P,0.001). Notably, extensive antibody responses to MnPV E2 were also detected in these cases. A prospective study revealed that E2 reactivity occurred by the age of 1 month. MnPV L1 antibodies were found at 2.5 months, indicating the initiation of productive viral infection. Thirty-one out of 34 L1-seropositive animals at the age of 4.5 months developed MnPV-associated tumours (positive predictive value577 %), and none of the seronegative animals developed skin papillomas (negative predictive value5100 %). MnPV E2 and L1 serology thus provides a powerful tool for monitoring early infection and skin tumour progression in M. coucha.
INTRODUCTIONPapillomaviruses (PVs) are small, non-enveloped DNA viruses that are frequently found in animals, particularly in vertebrates such as mammals and birds (Antonsson & Hansson, 2002). Different virus types infect epidermal or mucosal tissues and may cause diverse epithelial lesions such as papillomas and warts. PVs are represented by a large family of different genera, and specific types can induce cancerous lesions, for instance in rabbits, cattle and horses (Campo, 2002). An oncogenic potential has also been identified for human papillomaviruses (HPVs), which are by far the most heterogeneous group, with more than 100 types identified (de Villiers et al., 2004). Mucosal 'high-risk' HPV types have the potential to transform cells and are aetiologically linked to cancers, mostly in the uterine cervix (zur Hausen, 2002). Tumorigenicity and malignant progression are characterized by constitutive expression of the viral oncogenes E6/E7 and are often accompanied by integration of the viral DNA into the host genome. The oncogenic potential arises from their ability to interact with the cellular proliferation machinery, in particular the E6-induced degradation of p53 (Scheffner et al., 1993) and by E7 binding to pRB, releasing the S-phasepromoting factor E2F (Giarrè et al., 2001). During normal infection, the viruses replicate and mature in the course of epithelial differentiation, which is tightl...