Increased activated human T cell lymphotropic virus type I (HTLV-I) Tax11-19-specific memory and effector CD8⁺ cells in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis: Correlation with HTLV-I provirus load

To discern the T cell subtype associated with T cell differentiation, the expression of CD45RA and CD27 was measured from total CD8^high cells and from human T cell lymphotropic virus type I (HTLV-I) Tax11-19 peptide-specific CD8⁺ cells in peripheral blood lymphocytes of patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Phenotypically defined memory and/or effector cells (CD45RA^-CD27⁺, CD45RA⁺CD27^-, and CD45RA^- CD27^-) were increased in HAM/TSP CD8⁺ cells, compared with those of HTLV-I-seronegative healthy control subjects. The percentage of human leukocyte antigen (HLA)-DR-positive cells was also increased in CD8⁺ cells of HAM/TSP, compared with those in HLA-DR⁺CD8⁺ cells of healthy control subjects. HTLV-I provirus load correlated with the frequency of Tax11-19-specific CD8⁺ cells. The high frequency of memory and/or effector type HTLV-I Tax11-19-specific CD8⁺ cells suggests that continuous restimulation driven by HTLV-I antigens in vivo may be associated with the pathogenesis of HAM/TSP.