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.

• The used animals originated from the different breeding families available in the colony to represent the whole colony population.

Replicates
 You should report how often each experiment was performed  You should include a definition of biological versus technical replication  The data obtained should be provided and sufficient information should be provided to indicate the number of independent biological and/or technical replicates  If you encountered any outliers, you should describe how these were handled  Criteria for exclusion/inclusion of data should be clearly stated  High-throughput sequence data should be uploaded before submission, with a private link for reviewers provided (these are available from both GEO and ArrayExpress) Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission: • Sample sizes can be found in the "Results" section.
• MnPV is spread in the colony via natural infection. While some animals do not seroconvert throughout their life and are considered uninfected, infected animals have unequal infection histories regarding time point, viral load and therefore seroconversion.
• Based on discrepancy rates of 5% for L1SHORT + /L1LONGand 25% for L1SHORT -/L1LONG + among usable animals, and a general loss rate of 15% of the animals, the use of 60 animals gives a power of >80% (two-tailed McNemar's test, alpha = 5%) to differentiate between seroconversion against the long and the short L1 variant. Statistical reporting  Statistical analysis methods should be described and justified  Raw data should be presented in figures whenever informative to do so (typically when N per group is less than 10)  For each experiment, you should identify the statistical tests used, exact values of N, definitions of center, methods of multiple test correction, and dispersion and precision measures (e.g., mean, median, SD, SEM, confidence intervals; and, for the major substantive results, a measure of effect size (e.g., Pearson's r, Cohen's d)  Report exact p-values wherever possible alongside the summary statistics and 95% confidence intervals. These should be reported for all key questions and not only when the p-value is less than 0.05.
Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission: (For large datasets, or papers with a very large number of statistical tests, you may upload a single table file with tests, Ns, etc., with reference to sections in the manuscript.)

Group allocation
 Indicate how samples were allocated into experimental groups (in the case of clinical studies, please specify allocation to treatment method); if randomization was used, please also state if restricted randomization was applied  Indicate if masking was used during group allocation, data collection and/or data analysis Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission:  Regarding the animal experiments, this information is explicitly described in the "Results" section and the respective figure legends.  GST-ELISAs of all sera and for all antigens tested were performed in technical replicates (analysis of the same serum sample). No outliers were excluded.  Numbers of biological replicates (analysis of different cells from different passages) of the other experiments are indicated in the respective figure legends in the "Results" section.  The examination of the different monoclonal antibodies (Figure 7), however, was performed in technical replicates (analysis of the same antibody-containing hybridoma supernatant).
 Statistical tests used for the individual experiments are explained in detail within the "Material & Methods" section and individual information for the experiments are given in the respective figure legends.
 No grouping was performed.  However, when stated in the respective figure legend, the shown correlation only included sera with distinct reactivities, thereby excluding others (e.g. L1LONG + /L1SHORTsera in Figure 4C).