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

Hindawi Journal of Immunology Research Volume 2019, Article ID 6574828, 9 pages https://doi.org/10.1155/2019/6574828 Research Article The Role of NK Cells in the Control of Viral Infection in HTLV-1 Carriers Camila F. Amorim,1 Natália B. Carvalho ,1 José Abraão Neto,1 Silvane B. Santos,1,2 Maria Fernanda Rios Grassi,3 Lucas P. Carvalho,1,3,4 and Edgar M. Carvalho 1,3,4 1 Serviço de Imunologia, Complexo Hospitalar Universitário Professor Edgard Santos, Universidade Federal da Bahia, Salvador, Bahia, Brazil 2 Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Feira de Santana, Bahia, Brazil 3 Laboratório de Pesquisas Clínicas do Instituto de Pesquisas Gonçalo Muniz-Fiocruz/Bahia, Brazil 4 Instituto Nacional de Ciência e Tecnologia de Doenças Tropicais (CNPq), Salvador, Bahia, Brazil Correspondence should be addressed to Edgar M. Carvalho; Received 10 August 2018; Revised 11 December 2018; Accepted 9 January 2019; Published 28 February 2019 Academic Editor: Martin Holland Copyright © 2019 Camila F. Amorim et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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 CD56dim cells were decreased in HAM/TSP patients. The frequency of CD56+CD3cells was inversely correlated with proviral load in HC but not in HAM/TSP patients. HAM/TSP patients showed decreased frequency of CD56+ and CD56dim 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. 1. Introduction The immune response against viral infection is based on effector mechanisms from both the innate and adaptive immune response. Among these mechanisms, the cytotoxicity mediated by NK cells and cytotoxic CD8+ T cells (CTL) is responsible for killing infected cells. In human T lymphotropic virus type 1 (HTLV-1) infection, while NK cells seek to limit the replication of the virus-infected cells and proviral load in the early stages of infection, the CTLs are responsible for the control of viral latency [1]. NK cells as well as CTLs have the ability to directly kill infected cells through the production of perforins and granzymes in cytotoxic granules. These granules are released from cytotoxic cells surrounded initially by a lipid bilayer containing lysosomal membrane glycoproteins, including CD107a. Granzymes induce programmed cell death (apoptosis) after invading the cytoplasm of the target cell through the pores formed in the cell membranes by perforins [2]. Additionally, NK cells have the ability to mediate antibody-dependent cellular cytotoxicity (ADCC) through the receptor CD16 by binding to antibodies opsonizing infected cells, leading to apoptosis [3]. Classical NK cells express NCAM-1 (CD56) on their membranes in high or low intensity may or may not express CD16 and lack CD3 expression [4]. Over the past 15 years, a “new” population of cells expressing both CD3 and CD56 and called NKT cells has been described [5]. Half of these cells express CD16 and all of them express classical T cell receptors (TCRs) that 2 could recognize and respond to nonpeptide antigens like glycoproteins and polypeptides [5–8]. While NK cells have been mainly referred to as CD56+, CD56+CD3-, CD56+CD16+, CD56dim, and CD56bright, NKT cells are referred to as CD56+CD3+(CD16+/-). In HTLV-1 infection, about 3% of infected subjects will develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) [9]. In such case, an invasion of infected and uninfected cells to the central nervous system (CNS) triggers an inflammatory, chronic, local response leading to nervous tissue damage. The Tax viral protein is responsible for increasing the expression of IL-2 receptor as well as gene expression related to the inflammatory response, resulting in a substantial lymphocyte activation, proliferation, and cytokine production by both CD4+ and CD8+ T cells [10]. The proviral load and production of inflammatory cytokines are increased in HAM/TSP patients compared to HTLV-1 carriers [11–13]. The immune response developed by cytotoxic cells in HTLV-1 is essential for controlling the proviral load, which may be critical in preventing the development of HAM/TSP. It is known that CTLs kill HTLV-1-infected cells through the recognition of the Tax protein, but the efficiency of this killing is impaired due to decreased expression of Tax and increased expression of another viral immunogenic gene, the HZB in HTLV-1infected cells [14]. While the ligation of CD8+ T cells to cells expressing Tax is strong, these cells have an impaired ability to recognize HZB antigen. Moreover, there is a lack of studies evaluating the role of NK cells in HTLV-1. In this study, we phenotypically characterize NK and NKT cells in HTLV-1 infection, evaluate whether the expressions of CD16 and CD107a are altered, and correlate these findings with proviral load and development of HAM/TSP. 2. Methods 2.1. Ethical Statement. All HTLV-1-infected subjects were followed at the HTLV-1 clinic of the Complexo Hospitalar Universitário Professor Edgard Santos (COM-HUPES), Federal University of Bahia, Brazil. The study was approved by the Ethics Committee from the Federal University of Bahia, and all participants or patients were adults (>18 years old) and signed an informed consent. 2.2. Study Design and Case Definition. 39 HTLV-1-infected subjects participated in this study, of which 20 were HTLV-1 carriers (HC) and 19 were diagnosed with HAM/TSP. 10 seronegative individuals (SN) not infected with HTLV-1 participated as controls. A pregnant woman, patients with other neurologic diseases not associated with HTLV-1, individuals coinfected with other pathogens, or patients on immunosuppressing drugs were excluded from this study. The diagnosis of HTLV-1 infection was established by ELISA (...truncated)