Resistance of Leishmania (Viannia) braziliensis to nitric oxide: correlation with antimony therapy and TNF-alpha production.

BACKGROUND: Nitric oxide (NO) produced in macrophages plays a pivotal role as a leishmanicidal agent. A previous study has demonstrated that 20% of the L. (V.) braziliensis isolated from initial cutaneous lesions of patients from the endemic area of Corte de Pedra, Bahia, Brazil, were NO resistant. Additionally, 5 to 11% of the patients did not respond to three or more antimony treatments" (refractory patients). The aim of this study is to investigate if there is an association between the resistance of L. (V.) braziliensis to NO and nonresponsiveness to antimony therapy and cytokine production. METHODS: We evaluated the in vitro toxicity of NO against the promastigotes stages of L. (V.) braziliensis isolated from responsive and refractory patients, and the infectivity of the amastigote forms of these isolates against human macrophages. The supernatants from Leishmania infected macrophage were used to measure TNF-alpha and IL-10 levels. RESULTS: Using NaNO2 (pH 5.0) as the NO source, L. (V.) braziliensis isolated from refractory patients were more NO resistant (IC50 = 5.8 +/- 4.8) than L. (V.) braziliensis isolated from responsive patients (IC50 = 2.0 +/- 1.4). Four isolates were selected to infect human macrophages: NO-susceptible and NO-resistant L. (V.) braziliensis isolated from responsive and refractory patients. NO-resistant L. (V.) braziliensis isolated from refractory patients infected more macrophages stimulated with LPS and IFN-gamma at 120 hours than NO-susceptible L. (V.) braziliensis isolated from refractory patients. Also, lower levels of TNF-alpha were detected in supernatants of macrophages infected with NO-resistant L. (V.) braziliensis as compared to macrophages infected with NO-susceptible L. (V.) braziliensis (p < 0.05 at 2, 24 and 120 hours), while no differences were detected in IL-10 levels. CONCLUSION: These data suggest that NO resistance could be related to the nonresponsiveness to antimony therapy seen in American Tegumentary Leishmaniasis.

Impaired TNF, IL-1ß, and IL-17 production and increased susceptibility to Mycobacterium tuberculosis infection in HTLV-1 infected individuals.

IFN-γ and TNF play critical roles in the control of Mycobacterium tuberculosis infection. Despite leading to an exaggerated production of inflammatory cytokines, HTLV-1 infection increases the risk of developing tuberculosis (TB). However, the immune mechanisms accounting for this phenomenon are still unclear. The aim of this study was to evaluate immunological aspects of the HTLV-1/M. tuberculosis co-infection. In this cross-sectional study, the levels of TNF, IL-1ß, and IL-17 were determined by ELISA in the supernatants of either unstimulated or tuberculin purified protein derivative (PPD) stimulated peripheral blood mononuclear cells. Cells from HTLV-1 infected individuals produced lower levels of TNF following PPD stimulation compared to unstimulated cells. IL-1ß and IL-17 production by cells from HTLV-1/M. tuberculosis co-infected individuals was lower than in cells from patients with TB. Impairment in TNF, IL-1ß, and IL-17 production upon stimulation with mycobacterial antigens may contribute to the increased susceptibility to M. tuberculosis infection observed in HTLV-1 infected individuals.

Functional activity of monocytes and macrophages in HTLV-1 infected subjects.

The Human T lymphotropic virus type-1 (HTLV-1) infects predominantly T cells, inducing proliferation and lymphocyte activation. Additionally, HTLV-1 infected subjects are more susceptible to other infections caused by other intracellular agents. Monocytes/macrophages are important cells in the defense against intracellular pathogens. Our aims were to determine the frequency of monocytes subsets, expression of co-stimulatory molecules in these cells and to evaluate microbicidal ability and cytokine and chemokine production by macrophages from HTLV-1 infected subjects. Participants were 23 HTLV-1 carriers (HC), 22 HAM/TSP patients and 22 healthy subjects (HS) not infected with HTLV-1. The frequencies of monocyte subsets and expression of co-stimulatory molecules were determined by flow cytometry. Macrophages were infected with L. braziliensis or stimulated with LPS. Microbicidal activity of macrophages was determined by optic microscopy. Cytokines/chemokines from macrophage supernatants were measured by ELISA. HAM/TSP patients showed an increase frequency of intermediate monocytes, but expression of co-stimulatory molecules was similar between the groups. Macrophages from HTLV-1 infected individuals were infected with L. braziliensis at the same ratio than macrophages from HS, and all the groups had the same ability to kill Leishmania parasites. However, macrophages from HTLV-1 infected subjects produced more CXCL9 and CCL5, and less IL-10 than cells from HS. While there was no correlation between IFN-γ and cytokine/chemokine production by macrophages, there was a correlation between proviral load and TNF and CXCL10. These data showed a dissociation between the inflammatory response and microbicidal ability of macrophages from HTLV-1 infected subjects. While macrophages ability to kill an intracellular pathogen did not differ among HTLV-1 infected subjects, these cells secreted high amount of chemokines even in unstimulated cultures. Moreover the increasing inflammatory activity of macrophages was similar in HAM/TSP patients and HC and it was related to HTLV-1 proviral load rather than the high IFN-γ production observed in these subjects.