Expression of different L1 isoforms of Mastomys natalensis papillomavirus as mechanism to circumvent adaptive immunity.

Although many high-risk mucosal and cutaneous human papillomaviruses (HPVs) theoretically have the potential to synthesize L1 isoforms differing in length, previous seroepidemiological studies only focused on the short L1 variants, co-assembling with L2 to infectious virions. Using the multimammate mouse Mastomys coucha as preclinical model, this is the first study demonstrating seroconversion against different L1 isoforms during the natural course of papillomavirus infection. Intriguingly, positivity with the cutaneous MnPV was accompanied by a strong seroresponse against a longer L1 isoform, but to our surprise, the raised antibodies were non-neutralizing. Only after a delay of around 4 months, protecting antibodies against the short L1 appeared, enabling the virus to successfully establish an infection. This argues for a novel humoral immune escape mechanism that may also have important implications on the interpretation of epidemiological data in terms of seropositivity and protection of PV infections in general.

Cancer is not one disease but rather a collection of disorders. As such there are many reasons why someone may develop cancer during their lifetime, including the individual's family history, lifestyle and habits. Infections with certain viruses can also lead to cancer and human papillomaviruses are viruses that establish long-term infections that may result in cancers including cervical and anal cancer, and the most common form of cancer worldwide, non-melanoma skin cancer. The human papillomavirus, or HPV for short, is made up of DNA surrounded by a protective shell, which contains many repeats of a protein called L1. These L1 proteins stick to the surfaces of human cells, allowing the virus to get access inside, where it can replicate before spreading to new cells. The immune system responds strongly to HPV infections by releasing antibodies that latch onto L1 proteins. It was therefore not clear how HPV could establish the long-term infections and cause cancer when it was seeming being recognized by the immune system. Now, Fu et al. have used the Southern multimammate mouse, Mastomys coucha, as a model system for an HPV infection to uncover how papillomaviruses can avoid the immune response. This African rodent is naturally infected with a skin papillomavirus called MnPV which, like its counterpart in humans, can trigger the formation of skin warts and malignant skin tumors. Fu et al. took blood samples from animals that had been infected with the virus over a period of 76 weeks to monitor their immune response overtime. This revealed that, in the early stages of infection, the virus made longer-than-normal versions of the L1 protein. Further analysis showed that these proteins could not form the virus's protective shell but could trigger the animals to produce antibodies against them. Fu et al. went on to show that the antibodies that recognized the longer variants of L1 protein where "non-neutralizing", meaning that could not block the spread of the virus, which is a prerequisite for immunity. It was only after a delay of four months that the animals started making neutralizing antibodies that were directed against the shorter L1 proteins that actually makes up the virus's protective coat. These findings suggest that virus initially uses the longer version of the L1 protein as a decoy to circumvent the attention of the immune system and provide itself with enough time to establish an infection. The findings also have implications for other studies that have sought to assess the success of an immune response during a papillomavirus infection. Specifically, the delayed production of the neutralizing antibodies means that their presence does not necessarily indicate that a patient is not already infected by a papillomavirus that in the future may cause cancer.

Protective vaccination against papillomavirus-induced skin tumors under immunocompetent and immunosuppressive conditions: a preclinical study using a natural outbred animal model.

Certain cutaneous human papillomaviruses (HPVs), which are ubiquitous and acquired early during childhood, can cause a variety of skin tumors and are likely involved in the development of non-melanoma skin cancer, especially in immunosuppressed patients. Hence, the burden of these clinical manifestations demands for a prophylactic approach. To evaluate whether protective efficacy of a vaccine is potentially translatable to patients, we used the rodent Mastomys coucha that is naturally infected with Mastomys natalensis papillomavirus (MnPV). This skin type papillomavirus induces not only benign skin tumours, such as papillomas and keratoacanthomas, but also squamous cell carcinomas, thereby allowing a straightforward read-out for successful vaccination in a small immunocompetent laboratory animal. Here, we examined the efficacy of a virus-like particle (VLP)-based vaccine on either previously or newly established infections. VLPs raise a strong and long-lasting neutralizing antibody response that confers protection even under systemic long-term cyclosporine A treatment. Remarkably, the vaccine completely prevents the appearance of benign as well as malignant skin tumors. Protection involves the maintenance of a low viral load in the skin by an antibody-dependent prevention of virus spread. Our results provide first evidence that VLPs elicit an effective immune response in the skin under immunocompetent and immunosuppressed conditions in an outbred animal model, irrespective of the infection status at the time of vaccination. These findings provide the basis for the clinical development of potent vaccination strategies against cutaneous HPV infections and HPV-induced tumors, especially in patients awaiting organ transplantation.

Serological markers for papillomavirus infection and skin tumour development in the rodent model Mastomys coucha.

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 value=77 %), and none of the seronegative animals developed skin papillomas (negative predictive value=100 %). MnPV E2 and L1 serology thus provides a powerful tool for monitoring early infection and skin tumour progression in M. coucha.

A capture ELISA for monitoring papillomavirus-induced antibodies in Mastomys coucha.

The present report describes the development of an enzyme-linked immunosorbent assay (ELISA), whereby the first insights have been obtained into the humoral immune response to papillomavirus (PV) infections of the rodent Mastomys coucha, a natural model for papillomavirus-induced skin carcinogenesis. The established glutathione S-transferase (GST)-capture ELISA is based on a one-step purification of bacterially expressed antigens and was designed to detect serum antibodies against L1 capsid proteins of Mastomys natalensis papillomavirus (MnPV) and M. coucha papillomavirus 2 (McPV2). Both viruses are spread widely within the colony at the German Cancer Research Center. The animals are unique in that they spontaneously develop multiple epithelial tumors such as MnPV-induced papillomas and McPV2-induced condylomas. The humoral immune response of a cohort of 98 Mastomys was analysed and revealed a high prevalence of antibodies to L1 (MnPV: 36.7%, McPV2: 52.0%). Furthermore, the seroreactivity to both viruses was significantly increased in animals with the respective tumors (22 papillomas, 21 condylomas) as compared to 55 tumor-free controls (MnPV: p<0.0001; McPV2: p=0.0022). The identified assay conditions showed a high level of sensitivity (MnPV: 75.7%; McPV2: 85.7%) and reproducibility (MnPV: R(2)=0.83; McPV2: R(2)=0.79), validating the GST-capture ELISA as a powerful method for monitoring papillomavirus serology in M. coucha.

A novel rodent papillomavirus isolated from anogenital lesions in its natural host.

In the present work we describe both the prevalence and the histopathologic features of a novel papillomavirus (referred as McPV2) that naturally infects the rodent Mastomys coucha. Viral DNA could be isolated not only from anogenital wart-like lesions but also from healthy tissues (e.g. liver, kidney, spleen and intestine) without apparent signs of infection. Our finding of a second papillomavirus infecting M. coucha, phylogenetically very distant from the previously known MnPV, reinforces the growing view of warm-blooded vertebrates as being hosts for a number of different papilloma virus types that are not necessarily closely related. The histological descriptions of McPV2-associated anogenital lesions provided here, together with earlier knowledge on MnPV-associated skin carcinogenesis, define M. coucha as an excellent system where the link between infection towards malignancy can be studied in molecular, histochemical and immunological terms in immunocompetent animals. The availability of such an in vivo model also offers the unique opportunity to address defined questions about prophylactic and therapeutic strategies against different papillomavirus infections in their natural host. To date, McPV2 is the first rodent papillomavirus found in anogenital lesions.

High-field EPR investigations of Mn(III)Mn(IV) and Mn(II)Mn(III) states of dimanganese catalase and related model systems.

Multi-frequency EPR experiments at 9, 34 and 94 GHz are reported on the antiferromagnetically coupled mixed valence Mn(II)Mn(III) complex of manganese catalase and on several dinuclear manganese model systems. They are compared with similar experiments obtained earlier for the Mn(III)Mn(IV) states. It is demonstrated how accurate information on the G- and 55Mn hyperfine tensors can be derived from this approach. Furthermore, the effect of oxidation state, planarity of the manganese-oxygen core and the type of ligands bridging the manganese ions on the magnetic resonance parameters and the related electronic structure is investigated. 'Broken-symmetry' density functional calculations on two Mn(III)Mn(IV) complexes, including the superoxidized state of the catalase, are presented. The agreement between calculated and experimental EPR parameters and complex geometries is remarkably good. Implications of these results for the structure and function of the dimanganese catalase are discussed.

Multifrequency EPR analysis of the dimanganese cluster of the putative sulfate thiohydrolase SoxB of Paracoccus pantotrophus.

A detailed analysis of the EPR signatures at X-band and Q-band of an enzyme (SoxB) involved in sulfur oxidation from Paracoccus pantotrophus is presented. EPR spectra are attributed to an exchange-coupled dimanganese Mn(2)(II,II) complex. An antiferromagnetic exchange interaction of J=-7.0 (+/-1) cm(-1) (H=-2JS ( 1 ) S ( 2 )) is evidenced by a careful examination of the temperature dependence of the EPR spectra. The spin Hamiltonian parameters for a total spin of S ( T ) =1, 2 and 3 are obtained and an inter-manganese distance of 3.4 (+/-0.1) A is estimated. The comparison with exchange coupling and inter-manganese distance data of other dimanganese proteins and model compounds leads to a tentative assignment of the Mn bridging ligands to bis(mu-hydroxo) (mu-carboxylato).