Genetically Modified Live Attenuated Leishmania donovani Parasites Induce Innate Immunity through Classical Activation of Macrophages That Direct the Th1 Response in Mice

• Published in: Infection and immunity Vol. 83; no. 10; pp. 3800 - 3815
• Main Authors: Bhattacharya, Parna, Dey, Ranadhir, Dagur, Pradeep K, Kruhlak, Michael, Ismail, Nevien, Debrabant, Alain, Joshi, Amritanshu B, Akue, Adovi, Kukuruga, Mark, Takeda, Kazuyo, Selvapandiyan, Angamuthu, McCoy, Jr, John Philip, Nakhasi, Hira L
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01-10-2015
• Subjects: Adaptive Immunity; Animals; Cellular Microbiology: Pathogen-Host Cell Molecular Interactions; Chemokine CCL2 - genetics; Chemokine CCL2 - immunology; Chemokine CCL3 - genetics; Chemokine CCL3 - immunology; Female; Humans; Immunity, Innate; Interferon-gamma - genetics; Interferon-gamma - immunology; Interleukin-12 - genetics; Interleukin-12 - immunology; Interleukin-6 - genetics; Interleukin-6 - immunology; Leishmania donovani - genetics; Leishmania donovani - immunology; Leishmaniasis, Visceral - genetics; Leishmaniasis, Visceral - immunology; Leishmaniasis, Visceral - parasitology; Macrophages - immunology; Mice; Mice, Inbred BALB C; Th1 Cells - immunology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00184-15

Visceral leishmaniasis (VL) causes significant mortality and there is no effective vaccine. Previously, we have shown that genetically modified Leishmania donovani parasites, here described as live attenuated parasites, induce a host protective adaptive immune response in various animal models. In this study, we demonstrate an innate immune response upon infection with live attenuated parasites in macrophages from BALB/c mice both in vitro and in vivo. In vitro infection of macrophages with live attenuated parasites (compared to that with wild-type [WT] L. donovani parasites) induced significantly higher production of proinflammatory cytokines (tumor necrosis factor alpha [TNF-α], interleukin-12 [IL-12], gamma interferon [IFN-γ], and IL-6), chemokines (monocyte chemoattractant protein 1/CCL-2, macrophage inflammatory protein 1α/CCL-3, and IP-10), reactive oxygen species (ROS), and nitric oxide, while concomitantly reducing anti-inflammatory cytokine IL-10 and arginase-1 activities, suggesting a dominant classically activated/M1 macrophage response. The classically activated response in turn helps in presenting antigen to T cells, as observed with robust CD4(+) T cell activation in vitro. Similarly, parasitized splenic macrophages from live attenuated parasite-infected mice also demonstrated induction of an M1 macrophage phenotype, indicated by upregulation of IL-1β, TNF-α, IL-12, and inducible nitric oxide synthase 2 and downregulation of genes associated with the M2 phenotype, i.e., the IL-10, YM1, Arg-1, and MRC-1 genes, compared to WT L. donovani-infected mice. Furthermore, an ex vivo antigen presentation assay showed macrophages from live attenuated parasite-infected mice induced higher IFN-γ and IL-2 but significantly less IL-10 production by ovalbumin-specific CD4(+) T cells, resulting in proliferation of Th1 cells. These data suggest that infection with live attenuated parasites promotes a state of classical activation (M1 dominant) in macrophages that leads to the generation of protective Th1 responses in BALB/c mice.