in patients with MS, it seems reasonable to seek a potential relationship be- tween antibody titers and the course of MS. Although it has been suggested earlier that high anti-EBV titers in the cerebrospinal fluid result from the intrathecal syn- thesis of antibodies within the central nervous system, this has been clearly disproved by the latest studies [27]. Data on the clinical significance of high anti-EBNA-1 antibody titers are also controversial. Farrell et al. stud- ied the relationship of EBNA-1 IgG levels with disease subtypes, and with the appearance of new, gadolin- ium-enhancing MRI lesions, characteristic of acute in- flammation in 100 patients with MS [28]. Antibody titers were the highest in the relapsing-remitting form, whereas EBNA-1 IgG antibody levels were signifi- cantly lower in the clinically isolated syndrome (a sin- gle clinical event without relapse), and in the primary progressive disease type. Antibody titers exhibited a very significant, positive correlation with enhancing MRI lesions, with their size (T2 lesion circumference), and with the Expanded Disability Status Scale (EDSS – a quantitative index of disability in MS). According to the authors, their findings demonstrate a relationship between EBNA-1 IgG level and disease activity. Lüne- mann et al. [29] found that high anti-EBNA-1 antibody levels predict progression of the clinically isolated syn- drome to clinically definite MS – that is, an impending second relapse. Additionally, high titers correlate with the number of T2 lesions and of Barkhof criteria (re- quired to establish a diagnosis of MS by MRI), and with the EDDS score. Ingram et al., by contrast, did not find any significant relationship between the clinical activity of MS and EBNA-1 IgG levels [30].