Figure 1. . Cross-reactivity between human polyomavirus 9 (HPyV9), simian lymphotropic polyomavirus (LPyV), and Merkel cell polyomavirus (MCPyV) virus–like particles (VLPs). Correlation between A) seroreactivity of 325 serum samples from children and adults in Italy against HPyV9 VLPs and B) MCPyV VLPs and HPyV9 VLPs was analyzed by ELISA. Each point represents 1 serum sample. Correlation coefficients (Spearman ρ) were determined by using XLStat software (Addinsoft, Paris, France). Correlation coefficient was 0.842 in panel B and 0.139 in panel A. C) Titers of 15 serum samples from adults against HPyV9 VLPs and LPyV VLPs. Each point represents 1 serum sample. OD, optical density.