An additional 12 molecules, IL-1ra, IL-6, IL-7, IL-8, IL-9, IL-13, G-CSF, IP-10, MCP-1, PDGF-β, MIP1β and VEGF, were measured in the CSF samples but did not vary in PML and non-PML samples. This evidence concerns the gene IL13 and progressive multifocal leukoencephalopathy.