Clinical activity of folinic acid in patients with chronic fatigue syndrome.

A high incidence of severe B-cell immunodeficiency and chronic reactivated Epstein-Barr virus (EBV) infection in patients with chronic fatigue syndrome (CFS) is reported herein. Of the 58 patients evaluated, 100% had evidence of prior EBV exposure and 72% had evidence for reactivated EBV infection. Notably, 94% of CFS patients had B-cell immunodeficiency with a marked depletion of their CD19+IgM+ mature B-lymphocyte population.