Moreover, lymphocyte Fas level on a per-cell basis, expressed as mean fluorescence intensity (MFI), revealed an eight-fold increase in AC and a striking 19-fold increase in HAM/TSP (Kruskal–Wallis, Dunn’s post-test, p < 0.001), when compared to HC, but also when compared to AC (p < 0.05, Figure 2B), indicating that clinical progression to HAM/TSP is characterized by a predominant Fashi lymphocyte population, possibly primed for apoptosis. This evidence concerns the gene FAS and tropical spastic paraparesis.