FAS and tropical spastic paraparesis: Considering the significant correlation between in vitro Fas expression to age of onset in HAM/TSP, we resorted to genome-wide transcriptional analysis of PBMC treated in vitro with agonist or antagonist Fas mAb, to explore the broad pro/antiapoptotic, inflammatory, proliferative, and immunoregulatory Fas signaling pathways specifically triggered in HAM/TSP.