Finally, activated B cells (CD19 + CD69+) detected ex vivo were negatively associated with frailty, i.e. they were present at a 10% lower frequency for each increased degree on the CFS frailty scale, though this did not reach the cutoff for statistical significance (p = 0.075) [data not shown]. This evidence concerns the gene CD69 and myalgic encephalomeyelitis/chronic fatigue syndrome.