Leishmania Specific CD4 T Cells Release IFNγ That Limits Parasite Replication in Patients with Visceral Leishmaniasis

Abstract

Visceral leishmaniasis (VL) is associated with increased circulating levels of multiple pro-inflammatory cytokines and chemokines, including IL-12, IFNγ, and TNFα, and elevated expression of IFNγ mRNA in lesional tissue such as the spleen and bone marrow. However, an immunological feature of VL patients is that their peripheral blood mononuclear cells (PBMCs) typically fail to respond to stimulation with leishmanial antigen. Unexpectedly, it was recently shown that Leishmania specific IFNγ, can readily be detected when a whole blood stimulation assay (WBA) is used. We sought to define the conditions that permit whole blood cells to respond to antigen stimulation, and clarify the biological role of the IFNγ found to be released by cells from VL patients. CD4+ T cells were found to be crucial for and the main source of the IFNγ production in Leishmania stimulated whole blood (WB) cultures. Complement, antibodies and red blood cells present in whole blood do not play a significant role in the IFNγ response. The IFNγ production was reduced by blockade of human leukocyte antigen (HLA)-DR, indicating that the response to leishmanial antigens observed in WB of active VL patients is a classical HLA- T cell receptor (TCR) driven reaction. Most importantly, blockade of IFNγ in ex-vivo splenic aspirate cultures demonstrated that despite the progressive nature of their disease, the endogenous IFNγ produced in patients with active VL serves to limit parasite growth.

Tumor necrosis factor alpha neutralization has no direct effect on parasite burden, but causes impaired IFN-γ production by spleen cells from human visceral leishmaniasis patients

“…To further evaluate the role of TNF-α during VL, we next investigated how TNF-α neutralization affected antigen-specific responses in whole blood stimulated with SLA from VL patients (n=11) [33; 35]. In this short term assay, we found no effect of TNF-α blockade on the IL-10 or IFN-γ responses to SLA (Figure 6A & 6B).…”

“…Culture supernatant was collected following incubation for cytokine estimation by ELISA. Whole blood cell cultures were performed as described previously [32; 33]. In brief, heparinised blood was collected from VL patients and centrifuged at 450g.…”

A Subset of Neutrophils Expressing Markers of Antigen-Presenting Cells in Human Visceral Leishmaniasis

“…The long-standing belief that failure to clear VL is due to a defect in CD4 + T-cell interferon (IFN) γ release has required modification with recent evidence that lymphocytes behave quite differently in whole blood versus mononuclear cell preparations [25][26][27][28]. These findings underscore a need to dissect further the cellular responses underlying the inflammatory state during human VL.…”

Recent updates and perspectives on leishmaniasis

“…The role of interleukin 17 (IL-17), an inflammatory cytokine that plays a protective role against intracellular parasites, is controversial. Nascimento et al [67], evaluating the levels of IL-17A in the sera from patients with VL before and at different times after treatment with Glucantime, noted higher levels in the sera of patients with VL before treatment than in normal or endemic controls; during treatment, the levels of IL-17A decreased, but remained significantly higher than the values of normal subjects. This cytokine acts synergistically with IFN-γ, increasing nitric oxide production and leishmanicidal activity in infected macrophages.…”

“…Dendritic cellbased immunotherapy combined with antimony-based chemotherapy has been studied in mice, revealing a promising synergy. The IFNγ released by cells, particularly by CD+ T cells, from VL patients serves to limit parasite growth [67]. Arabinosylated lipoarabinomannan, a Toll-like receptor 2-ligand isolated from Mycobacterium smegmatis, has a strong immunomodulatory property, giving protection against L. donovani infection by restoring IFN-γ responsiveness important for protection against L. donovani-susceptible hosts [68].…”