CD4 and tropical spastic paraparesis: Polarized aggregates of infectious HTLV-1 virions, identified as biofilms, have been observed in HTLV-1-infected T-cell lines and at the surface of primary CD4(+) T-cells isolated from HAM/TSP patients or asymptomatic HTLV-1 carriers (24), suggesting a conserved role in HTLV-1 pathogenesis.