S100A9 and tropical spastic paraparesis: We identified two plasma proteins whose abundance in HTLV-1-infected individuals was significantly and independently associated with the presence of HAM: β2-microglobulin and Calgranulin B. Moreover, the plasma β2-microglobulin concentration was significantly correlated with the degree of disability resulting from HAM as measure by the 10 m timed walk (Figure 4).