CSF and plasma levels of IL-6 are correlated in conditions involving neuronal injury (e.g., subarachnoid hemorrhage) and chronic systemic inflammation (e.g., fibromyalgia), and a prior study using an experimental challenge with bacterial LPS showed tandem increases in CSF and peripheral blood IL-6 in humans, suggesting that CSF IL-6 may at least partially reflect peripheral inflammation39,83,84. This evidence concerns the gene IL6 and subarachnoid hemorrhage.