CXCL13 and myalgic encephalomeyelitis/chronic fatigue syndrome: Comparison of CXCL13 serum levels between the ME/CFS and control cohorts revealed no significant difference (mean ± SEM 33.29 ± 126.7 versus 15.27 ± 10.41, P = 0.2152 by 2-tailed Mann-Whitney U test).