The Role of NK Cells in the Control of Viral Infection in HTLV-1 Carriers

The cytotoxic activities of CD8(+) T cells have been considered the main defense mechanism against the human T lymphotropic virus type 1 (HTLV-1). As with CD8(+) T cells, NK cells can perform cytotoxic degranulation with production of cytotoxic mediators, such as perforins and granzymes. NK cells are also responsible for antibody-dependent cellular cytotoxicity (ADCC) against infected cells, but few studies have evaluated the role of NK cells in HTLV-1 infection. The aim of this study was to characterize the subsets and measure the frequency of NK cells in HTLV-1 carriers (HC) and in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and correlate these findings with the proviral load and development of HAM/TSP. The diagnosis of HTLV-1 infection was performed with a detection antibody against viral antigens by ELISA and confirmed by Western blot. Phenotypic characterization of NK cells was performed by flow cytometry. The frequencies of CD56(+), CD56(+)CD3(-), CD56(+)CD16(+), and CD56(dim) cells were decreased in HAM/TSP patients. The frequency of CD56(+)CD3(-) cells was inversely correlated with proviral load in HC but not in HAM/TSP patients. HAM/TSP patients showed decreased frequency of CD56(+) and CD56(dim) cells expressing CD16, the main receptor for ADCC. These data indicate that NK cells may play a key role in the control of HTLV-1 infection by preventing the progression of HC to HAM/TSP.