CD4 and tropical spastic paraparesis: We previously reported the significantly increased adherence to ECs and subsequent transmigration through ECs of activated CD4+ T cells with heightened LFA-1 expression in the peripheral blood T cells of HAM/TSP patients as mentioned above [30,31], suggesting the upregulation of signaling based on integrin/ligand interaction in the peripheral blood CD4+ T cells of HAM/TSP patients.