The negative correlation between the percentage of B cells in the CSF and age that we found in people with primary progressive multiple sclerosis is likely a consequence of the significant decrease of the number and percentages of B cells with age, which has been extensively described in previous studies.59-63 Our study also supports previous observations that the percentage of CD20dim T cells increases with age64 and reports an age-associated expansion of specifically the CD20dim CD4+ and not CD8+ CD20dim memory T cells. The gene discussed is CD4; the disease is primary progressive multiple sclerosis.