IL4 and progressive multifocal leukoencephalopathy: However, with natalizumab, there are questions regarding whether the benefit of the drug justifies the risk of progressive multifocal leukoencephalopathy, so perhaps LAQ may be a safer alternative (Schwab et al., 2015) The mechanism whereby this down-regulation occurs is not known, but a study has shown that IL-4 suppresses VLA-4 expression thus perhaps the ability of LAQ to induce TH2 cells and IL-4 production influences VLA-4 expression (Sasaki et al., 2009).