Natural killer (NK) cells in HTLV-I-associated myelopathy/tropical spastic paraparesis - decrease in NK cell subset populations and activity in HTLV-I seropositive individuals

We examined natural killer (NK) cell activity and NK cell subset populations in 18 patients with HTLV-I associated myelopathy (HAM)/tropical spastic paraparesis (TSP), ten HTLV-I seropositive asymptomatic carriers and 20 seronegative healthy controls. The NK cell activity was significantly decreased in HAM/TSP, compared with that in controls. The percentages of NK cell subsets, such as CD16⁺, CD11b⁺, CD56⁺, CD16⁺CD56^-, CD16^-CD56⁺, CD16⁺CD8^-, or CD16⁺CD3⁺ cells were significantly decreased in HAM/TSP patients. Of particular interest is that the percentage of CD16⁺CD3⁺ cells, which have a wide spectrum of cytotoxic properties commonly seen in NK, lymphokine activated killer (LAK) and antibody-dependent cellular-cytotoxic (ADCC) effector cells, was significantly decreased in HAM/TSP as compared to asymptomatic carriers as well as controls. The percentage of CD16⁺CD3⁺ cells correlated inversely with the value of spontaneous proliferation of peripheral blood lymphocytes (SPP), which is a characteristic change observed in HAM/TSP.