CXCL9 and tropical spastic paraparesis: The most important hallmarks of HAM/TSP include chronic inflammation in the cerebro-spinal fluid (CSF); increased plasma levels of pro-inflammatory cytokines (i.e. IL-4, IL-6, IL-8, IFN-Υ and TNF-α); CD4+ T cells, which continuously and spontaneously produce IFN- Υ, TNF-α, IL-6 and IL-1β; and increased levels of CXCL10, CXCL9 and CXCR3 in the CSF, as well as numerous indicators of chronic inflammation in the CSF [2, 4].