CD40LG and infection: This combination of an early intrathecal total IgM synthesis, a neutrophilic pleocytosis, and a severe disruption of the blood–CSF–barrier, as demonstrated by an increased age-adjusted CSF/serum albumin ratio about one week after first symptoms, is even more suggestive of a bacterial than a viral ME, and it might direct the physician’s attention away from the infection with a (Flavi)virus [13,35].