Although not demonstrated in HTLV-1 infected patients, a positive correlation between spontaneous lymphoproliferation and CD80 expression was observed in HTLV-2-infected patients [26], indicating a possible mechanism for simultaneous upregulation of both deleterious candidate biomarkers, IFN-γ [52] and CD80 [this study], in HAM/TSP pathogenesis. Here, CD80 is linked to tropical spastic paraparesis.