Cross-sectional case–control studies have revealed that some BD patients exhibit elevated cerebrospinal fluid (CSF) levels of IL-1 β, IL-6 [225], MCP-1 [226] (discussed in the previous section), and YKL-40 [226], a protein expressed by neurons, astrocytes, and especially microglia, whose levels increase in chronic inflammatory conditions [227]. Here, IL6 is linked to Behcet disease.