CD4+ T Cell-Dependent Macrophage Activation Modulates Sustained PS Exposure on Intracellular Amastigotes of Leishmania amazonensis

Abstract

Leishmania amazonensis amastigotes can make use of surface-exposed phosphatidylserine (PS) molecules to promote infection and non-classical activation of macrophages (MΦ), leading to uncontrolled intracellular proliferation of the parasites. This mechanism was quoted as apoptotic mimicry. Moreover, the amount of PS molecules exposed on the surface of amastigotes correlates with the susceptibility of the host. In this study, we tested whether host cellular responses influence PS expression on intracellular amastigotes. We found that the level of PS exposure on intracellular amastigotes was modulated by CD4 + T cell and MΦ activation status in vitro and in vivo . L. amazonensis infection generated a Th1/Th2-mixed cytokine profile, providing the optimal MΦ stimulation that favored PS exposure on intracellular amastigotes. Maintenance of PS exposed on the parasite was dependent on low, but sustained, levels of nitric oxide and polyamine production. Amastigotes obtained from lymphopenic nude mice did not expose PS on their surface, and adoptive transfer of CD4 + T cells reversed this phenotype. In addition, histopathological analysis of mice treated with anti-PS antibodies showed increased inflammation and similarities to nude mouse lesions. Collectively, our data confirm the role of pathogenic CD4 + T cells for disease progression and point to PS as a critical parasite strategy to subvert host immune responses.

Immunization with the HisAK70 DNA Vaccine Induces Resistance against Leishmania Amazonensis Infection in BALB/c Mice

“…[21][22][23]. An effective vaccine must also induce the development of an antiparasitic CD4 + and CD8 + T-cell-mediated Th1 immunity, which is characterized by the production of interferon-γ (IFN-γ), interleukin-2 (IL-2) and IL-12, among other pro-inflammatory cytokines [24,25]. On the other hand, susceptible murine models, such as the BALB/c mice model of CL induced by L. amazonensis, are associated with the development of a Th2-type response, with high levels of parasite-specific induction of IL-4 and IL-10 along with elevated antileishmanial immunoglobulin G1 (IgG1) antibody production [26][27][28][29].…”

Leishmania Immunity: Advancing Immunotherapy and Vaccine Development

“…IL-12 is a key cytokine that induces the T-helper 1 (Th1) response which is essential for parasite elimination in infected macrophages [44][45][46]. It has been shown that the outcome of Leishmania infection in macrophages depends on their activation status [42,[47][48][49]. Classical activation of macrophages is mediated by Interferon gamma (IFN-γ), an effector cytokine secreted by CD4 + T helper type 1 (Th1) cells, CD8 + T cells, and natural killer (NK) cells [50].…”

Apoptotic mimicry as a strategy for the establishment of parasitic infections: parasite- and host-derived phosphatidylserine as key molecule

“…Amastigote forms are adapted to the higher temperatures and lower pH encountered in mammalian hosts; therefore, they should not display apoptotic features in these conditions [33,34]. However, when purified from mice lesions or macrophages in in vitro cultures, amastigotes expose PS in the outer leaflet of the plasma membrane, despite the maintenance of viability, morphology, and ability to infect other cells, animals, phlebotomine sandflies and to differentiate into promastigote forms [5,[35][36][37]. This observation led to the question whether PS exposure on amastigotes plays a role in the normal biology of the parasite, unrelated to cell death.…”

“…It was observed that the recognition of PS on the surface of these parasites is fundamental for amastigote uptake by macrophages and, most importantly, to induce a permissive status in the host cell, allowing parasite intracellular growth and maintenance [5,[35][36][37]. During amastigote infection, PS is able to induce TGF-β1 and IL-10 production by macrophages, which decreases NO production [5,35,36]. Actually, the events triggered by PS recognition on amastigotes are similar to the ones observed during apoptotic cell recognition, as depicted in Fig.…”

“…Interestingly, it was observed that an intrinsic pressure from the immune system is responsible to induce PS exposure on intracellular amastigotes. Amastigotes obtained from infected immune-deficient mice do not expose PS at their surface and the adoptive transfer of immune-competent primed T lymphocytes revert this phenotype [36]. Experimental evidences suggest that NO synthesis pathway is responsible for the induction of PS exposure on intracellular amastigotes, since the immune activation of infected iNOS (inducible nitric oxide synthase) KO macrophages does not stimulate PS exposure on the intracellular parasites.…”