TLR9 and MyD88 Are Crucial for the Development of Protective Immunity to Malaria

Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
The Journal of Immunology (Impact Factor: 4.92). 04/2012; 188(10):5073-85. DOI: 10.4049/jimmunol.1102143
Source: PubMed


Effective resolution of malaria infection by avoiding pathogenesis requires regulated pro- to anti-inflammatory responses and the development of protective immunity. TLRs are known to be critical for initiating innate immune responses, but their roles in the regulation of immune responses and development of protective immunity to malaria remain poorly understood. In this study, using wild-type, TLR2(-/-), TLR4(-/-), TLR9(-/-), and MyD88(-/-) mice infected with Plasmodium yoelii, we show that TLR9 and MyD88 regulate pro/anti-inflammatory cytokines, Th1/Th2 development, and cellular and humoral responses. Dendritic cells from TLR9(-/-) and MyD88(-/-) mice produced significantly lower levels of proinflammatory cytokines and higher levels of anti-inflammatory cytokines than dendritic cells from wild-type mice. NK and CD8(+) T cells from TLR9(-/-) and MyD88(-/-) mice showed markedly impaired cytotoxic activity. Furthermore, mice deficient in TLR9 and MyD88 showed higher Th2-type and lower Th1-type IgGs. Consequently, TLR9(-/-) and MyD88(-/-) mice exhibited compromised ability to control parasitemia and were susceptible to death. Our data also show that TLR9 and MyD88 distinctively regulate immune responses to malaria infection. TLR9(-/-) but not MyD88(-/-) mice produced significant levels of both pro- and anti-inflammatory cytokines, including IL-1β and IL-18, by other TLRs/inflammasome- and/or IL-1R/IL-18R-mediated signaling. Thus, whereas MyD88(-/-) mice completely lacked cell-mediated immunity, TLR9(-/-) mice showed low levels of cell-mediated immunity and were slightly more resistant to malaria infection than MyD88(-/-) mice. Overall, our findings demonstrate that TLR9 and MyD88 play central roles in the immune regulation and development of protective immunity to malaria, and have implications in understanding immune responses to other pathogens.

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Available from: Nagaraj Gowda, Dec 23, 2013
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    • "While blood stage parasite PAMPs such as GPI or hemozoin/DNA have been identified (Gowda, 2007; Erdman et al., 2008), sporozoite PAMPs that could play a role in the skin remain to be defined. Thus, parasite-host factors during vector-mediated malaria transmission could be a determinant for activating the innate immune responses that would have an impact in the onset of parasite-specific adaptive immunity (Coban et al., 2007; Franklin et al., 2009; Gowda et al., 2012). The arthropod vector also plays a role on this battlefield scenario because the Anopheles mosquito harbors an associated, symbiotic microbiome that is beneficial to host life relatedtraits , such as development, fecundity dietary, adaptation to the environment and immunity against pathogenic microorganisms, including Plasmodium parasites, in its digestive tract (Dinparast Djadid et al., 2011; Wang et al., 2011; Alvarez et al., 2012; Jiang et al., 2012; Ngwa et al., 2013). "
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    ABSTRACT: Plasmodium sporozoites and liver stages express antigens that are targeted to the MHC-Class I antigen-processing pathway. After the introduction of Plasmodium sporozoites by Anopheles mosquitoes, bone marrow-derived dendritic cells in skin-draining lymph nodes are the first cells to cross-present parasite antigens and elicit specific CD8(+) T cells. One of these antigens is the immunodominant circumsporozoite protein (CSP). The CD8(+) T cell-mediated protective immune response against CSP is dependent on the interleukin loop involving IL-4 receptor expression on CD8(+) cells and IL-4 secretion by CD4(+) T cell helpers. In a few days, these CD8(+) T cells re-circulate to secondary lymphoid organs and the liver. In the liver, the hepatic sinusoids are enriched with cells, such as dendritic, sinusoidal endothelial and Kupffer cells, that are able to cross-present MHC class I antigens to intrahepatic CD8(+) T cells. Specific CD8(+) T cells actively find infected hepatocytes and target intra-cellular parasites through mechanisms that are both interferon-γ-dependent and -independent. Immunity is mediated by CD8(+) T effector or effector-memory cells and, when present in high numbers, these cells can provide sterilizing immunity. Human vaccination trials with recombinant formulations or attenuated sporozoites have yet to achieve the high numbers of specific effector T cells that are required for sterilizing immunity. In spite of the limited number of specific CD8(+) T cells, attenuated sporozoites provided multiple times by the endovenous route provided a high degree of protective immunity. These observations highlight that CD8(+) T cells may be useful for improving antibody-mediated protective immunity to pre-erythrocytic stages of malaria parasites.
    Frontiers in Microbiology 08/2014; 5:440. DOI:10.3389/fmicb.2014.00440 · 3.99 Impact Factor
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    • "Extensive evidence exists of immune stimulation through TLR signaling demonstrating increased chemokine and cytokine production, up-regulation of co-stimulatory molecules and cell proliferation [15,16]. Common members of signaling networks, especially MyD88 [17-19], have also been observed to play a critical function in responses to PAMPs [20,21]. Currently, adjuvant selection for vaccines is determined primarily through extensive and costly empirical clinical testing of multiple adjuvant systems [22]. "
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    ABSTRACT: Vaccines play a vital role in modern medicine. The development of novel vaccines for emerging and resistant pathogens has been aided in recent years by the use of novel adjuvants in subunit vaccines. A deeper understanding of the molecular pathways behind adjuvanticity is required to better select immunostimulatory molecules for use in individual vaccines. To this end, we have undertaken a study of the essential signaling pathways involved in the innate and adaptive immune responses to the Neisseria meningitidis outer membrane protein Porin B (PorB). We have previously demonstrated that PorB is an agonist of Toll-Like Receptor 2 (TLR2) and acts as an adjuvant in vaccines for protein, carbohydrate and lipopolysaccharide antigens using murine models. Here we demonstrate NFκB translocation following stimulation with PorB only occurs in the presence of TLR2. IL-6 and TNF-α secretion was shown to be MAPK dependent. Surface expression of activation markers on macrophages, including CD40, CD69, and CD86, was increased following PorB stimulation in vitro. Interestingly, some upregulation of CD54 and CD69 was still observed in macrophages obtained from TLR2 KO mice, indicating a possible non-TLR2 mediated activation pathway induced by PorB. In a murine vaccination model, using ovalbumin as the antigen and PorB as the adjuvant, a decreased antigen-specific IgG production was observed in TLR2 KO mice; adjuvant-dependent increased IgG production was entirely ablated in MyD88 KO mice. These observations demonstrate the importance of the above pathways to the adjuvant activity of PorB. The potential TLR2 independent effect is currently being explored.
    PLoS ONE 12/2013; 8(12):e82171. DOI:10.1371/journal.pone.0082171 · 3.23 Impact Factor
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    • "Malaria parasites induce strong pro-inflammatory cytokine responses in both human and mouse DCs predominantly through TLR9-mediated recognition [32], [39], [47]. Unlike in mice, where both myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) express TLR9 [48], in humans, pDCs but not mDCs express TLR9 [49]–[51]. "
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    ABSTRACT: The scavenger receptor CD36 plays important roles in malaria, including the sequestration of parasite-infected erythrocytes in microvascular capillaries, control of parasitemia through phagocytic clearance by macrophages, and immunity. Although the role of CD36 in the parasite sequestration and clearance has been extensively studied, how and to what extent CD36 contributes to malaria immunity remains poorly understood. In this study, to determine the role of CD36 in malaria immunity, we assessed the internalization of CD36-adherent and CD36-nonadherent Plasmodium falciparum-infected red blood cells (IRBCs) and production of pro-inflammatory cytokines by DCs, and the ability of DCs to activate NK, and T cells. Human DCs treated with anti-CD36 antibody and CD36 deficient murine DCs internalized lower levels of CD36-adherent IRBCs and produced significantly decreased levels of pro-inflammatory cytokines compared to untreated human DCs and wild type mouse DCs, respectively. Consistent with these results, wild type murine DCs internalized lower levels of CD36-nonadherent IRBCs and produced decreased levels of pro-inflammatory cytokines than wild type DCs treated with CD36-adherent IRBCs. Further, the cytokine production by NK and T cells activated by IRBC-internalized DCs was significantly dependent on CD36. Thus, our results demonstrate that CD36 contributes significantly to the uptake of IRBCs and pro-inflammatory cytokine responses by DCs, and the ability of DCs to activate NK and T cells to produce IFN-γ. Given that DCs respond to malaria parasites very early during infection and influence development of immunity, and that CD36 contributes substantially to the cytokine production by DCs, NK and T cells, our results suggest that CD36 plays an important role in immunity to malaria. Furthermore, since the contribution of CD36 is particularly evident at low doses of infected erythrocytes, the results imply that the effect of CD36 on malaria immunity is imprinted early during infection when parasite load is low.
    PLoS ONE 10/2013; 8(10):e77604. DOI:10.1371/journal.pone.0077604 · 3.23 Impact Factor
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