IL-6 concentrations increased over time (24 to 72 h), peaking in the HTLV+ HAM/TSP+ group, which showed significantly higher levels than the HTLV+ HAM/TSP− group (p ≤ 0.01) and both positive (MT-2 cells) and negative controls (p ≤ 0.0001). This evidence concerns the gene IL6 and tropical spastic paraparesis.