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English: FIGURE 2. HTLV-1 clinical forms and their pulmonary alterations. After HTLV-1 infection, three clinical forms may occur. (A) ATL/L Clonal proliferation of infected cells, through the actions of Tax and others viral proteins, causes alterations and errors in the host genome, leading to the onset of ATL cells, reduced numbers of naive T cells and T reg cells (CD4+ and CD25+). ATL/L also induces higher expression of Forkhead Fox P3+ and anti-inflammatory cytokines, such as IL-10, leading to immunodeficiency and opportunistic infections as Tuberculosis. (B) HAM/TSP The increased levels of lymphocytes (CD4+ and CD25+), inflammatory cytokines as Interleukine 2 (IL-2), Interleukine 12 (IL-12), and Interferon-γ (IFN-γ), and inflammatory chemokines such as Macrophage inflammatory protein (MIP-1α) and IP-10 in the BALF, leading to the development of alveolitis and bronchiolitis. (C) Asymptomatic Carriers do not develop visible symptoms but exhibit tumor necrosis factor-α (TNF-α), Interleukine 1-β (IL-1β) and Interleukine 17 (IL-17) low expression, which makes these individuals more susceptible to coinfection by Mycobacterium tuberculosis, developing more severe forms of the disease.