Plasmodium falciparum-derived uric acid precipitates induce maturation of dendritic cells

Association of uric acid levels with severity of Plasmodium infections: a systematic review and meta-analysis

Elevated uric acid (UA) levels have been reported in malaria patients and are particularly prominent in severe malaria cases. This study aims to synthesize the difference in UA levels between malaria patients and uninfected controls, and between patients with severe and non-severe malaria. A comprehensive literature search was carried out across databases such as Embase, MEDLINE, Ovid, PubMed, Scopus, ProQuest, and Google Scholar to identify relevant studies for inclusion. The methodological quality of the included studies was evaluated independently by two reviewers using the JBI critical appraisal tool for observational studies. A meta-analysis was performed to calculate the pooled effect sizes, expressed as Hedges' g, with 95% confidence intervals (CIs). The Hedges' g was pooled using the random-effects model. An initial search yielding a total of 1122 articles, and a final total of 19 studies being included in the review. Elevated UA levels were observed more prominently in malaria patients, especially those with severe manifestations, when compared to uninfected controls. The conducted meta-analysis demonstrated a significant elevation in UA levels in patients suffering from malaria as compared to uninfected controls (P < 0.01, Hedges's g = 1.40, 95% CI 0.84-1.95, I2 = 95.81, 16 studies). The conducted meta-analysis demonstrated a significant elevation in UA levels in patients suffering from severe malaria as compared to non-severe malaria (P < 0.01, Hedges's g = 3.45, 95% CI 1.06-5.83, I2 = 98.73, 6 studies). In summary, these findings provide valuable insights into the potential use of UA as a biomarker for malaria infection and determination of its severity. Further research is needed to validate these findings and to explore the underlying mechanisms that contribute to the elevation of UA levels during malaria infection.

A low serum uric acid concentration predicts a poor prognosis in adult patients with candidemia

This study aimed to determine the relation of serum uric acid (UA) level with outcomes in adults with candidemia. Medical records of patients with candidemia treated from 2014 to 2017 were retrospectively reviewed. Patients were age- and sex-matched with healthy control subjects. The associations of UA and cystatin C (CysC) levels with diagnosis and prognosis of candidemia were determined. Sixty-four patients with candidemia (13 females and 51 males; mean age 48.5 years) and 64 matched control subjects were included. The median UA level of patients with candidemia was 255 μmol/L (range, 158–395 μmol/L), and of healthy controls was 398 μmol/L (range, 345–450 μmol/L) (P < 0.001). The median CysC level of patients with candidemia was 1.07 mg/L (range, 0.89–1.59 mg/L), and of the healthy controls was 0.82 mg/L (range, 0.74–0.95 mg/L) (P < 0.001). Patients with a favorable prognosis had significantly higher serum UA levels than those with a poor prognosis (181 μmol/L vs 344 μmol/L; P = 0.001). It was indicated that the estimated OR for UA was significantly > 1 (P = 0.009), and the AUC was 0.734. In summary, a lower serum UA level is associated with a diagnosis of candidemia, and a poor outcome.

Whole Blood Dendritic Cell Cytokine Production Assay

This protocol outlines a method for the timely detection of intracellular cytokines produced by activated dendritic cells (DC) in human whole blood. The quantification of cytokines is used to measure DC immune responsiveness, providing information on the breadth, strength, and DC subtypes responding spontaneously and to specific stimulation with toll-like receptor (TLR) ligands or parasite-infected erythrocytes. DC subsets, plasmacytoid DC, CD1c⁺ DC, CD141⁺ DC, and CD16⁺ DC, are examined in their natural environment of plasma and blood cells (erythrocytes, neutrophils, platelets, and leukocytes) enabling disease, medication, nutritional, and hematological effects on DC function to be examined in vaccine studies, ageing, health, and disease.

In situ Synthesized Monosodium Urate Crystal Enhances Endometrium Decidualization via Sterile Inflammation During Pregnancy

High level of uric acid (UA) is the major origin of gout, and is highly associated with various pregnant complications, such as preeclampsia and gestational diabetes. However, UA’s level and role in the very early stage of pregnancy has not been uncovered. This study aims to investigate the relevance of serum UA and decidualization, an essential process for the establishment and maintenance of pregnancy in women and mice during the early stage of pregnancy. In this study, we first proved that expression level of UA synthase xanthine dehydrogenase (XDH) is highly increased along with decidualization of endometrial stromal cells in both in vitro and in vivo models. Furthermore, serum and endometrial levels of UA are higher in mice with decidualized uterin horn and in vitro decidualized stromal cells. The existence of monosodium urate (MSU) crystal was also confirmed by immunostaining. Next, the roles of MSU on decidualization were explored by both in vitro and in vivo models. Our data shows MSU crystal but not UA enhances the decidualization response of endometrial stromal cells, via the upregulation of inflammatory genes such Ptgs2 and Il11. inhibiting of Cox-2 activity abolishes MSU crystal induced higher expression of decidualization marker Prl8a2. At last, in women, we observed enriched expression of XDH in decidua compare to non-decidualized endometrium, the serum level of UA is significantly increased in women in very early stage of pregnancy, and drop down after elective abortion. In summary, we observed an increased serum UA level in the early stage of women’s pregnancy, and proved that the increased level of UA results from the expressed XDH in decidualizing endometrium of both human and mouse, leading to the formation of MSU crystal. MSU crystal can enhance the decidualization response via inflammatory pathways. Our study has uncovered the association between UA, MSU, and decidualization during the early stage of pregnancy.

Dendritic Cell Responses and Function in Malaria

Malaria remains a serious threat to global health. Sustained malaria control and, eventually, eradication will only be achieved with a broadly effective malaria vaccine. Yet a fundamental lack of knowledge about how antimalarial immunity is acquired has hindered vaccine development efforts to date. Understanding how malaria-causing parasites modulate the host immune system, specifically dendritic cells (DCs), key initiators of adaptive and vaccine antigen-based immune responses, is vital for effective vaccine design. This review comprehensively summarizes how exposure to Plasmodium spp. impacts human DC function in vivo and in vitro. We have highlighted the heterogeneity of the data observed in these studies, compared and critiqued the models used to generate our current understanding of DC function in malaria, and examined the mechanisms by which Plasmodium spp. mediate these effects. This review highlights potential research directions which could lead to improved efficacy of existing vaccines, and outlines novel targets for next-generation vaccine strategies to target malaria.

Dendritic Cells and Their Multiple Roles during Malaria Infection

Dendritic cells (DCs) play a central role in the initiation of adaptive immune responses, efficiently presenting antigens to T cells. This ability relies on the presence of numerous surface and intracellular receptors capable of sensing microbial components as well as inflammation and on a very efficient machinery for antigen presentation. In this way, DCs sense the presence of a myriad of pathogens, including Plasmodium spp., the causative agent of malaria. Despite many efforts to control this infection, malaria is still responsible for high rates of morbidity and mortality. Different groups have shown that DCs act during Plasmodium infection, and data suggest that the phenotypically distinct DCs subsets are key factors in the regulation of immunity during infection. In this review, we will discuss the importance of DCs for the induction of immunity against the different stages of Plasmodium, the outcomes of DCs activation, and also what is currently known about Plasmodium components that trigger such activation.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

Solving ptychography with a convex relaxation

Ptychography is a powerful computational imaging technique that transforms a collection of low-resolution images into a high-resolution sample reconstruction. Unfortunately, algorithms that currently solve this reconstruction problem lack stability, robustness, and theoretical guarantees. Recently, convex optimization algorithms have improved the accuracy and reliability of several related reconstruction efforts. This paper proposes a convex formulation of the ptychography problem. This formulation has no local minima, it can be solved using a wide range of algorithms, it can incorporate appropriate noise models, and it can include multiple a priori constraints. The paper considers a specific algorithm, based on low-rank factorization, whose runtime and memory usage are near-linear in the size of the output image. Experiments demonstrate that this approach offers a 25% lower background variance on average than alternating projections, the ptychographic reconstruction algorithm that is currently in widespread use.

High numerical aperture Fourier ptychography: principle, implementation and characterization

Fourier ptychography (FP) utilizes illumination control and computational post-processing to increase the resolution of bright-field microscopes. In effect, FP extends the fixed numerical aperture (NA) of an objective lens to form a larger synthetic system NA. Here, we build an FP microscope (FPM) using a 40X 0.75NA objective lens to synthesize a system NA of 1.45. This system achieved a two-slit resolution of 335 nm at a wavelength of 632 nm. This resolution closely adheres to theoretical prediction and is comparable to the measured resolution (315 nm) associated with a standard, commercially available 1.25 NA oil immersion microscope. Our work indicates that Fourier ptychography is an attractive method to improve the resolution-versus-NA performance, increase the working distance, and enlarge the field-of-view of high-resolution bright-field microscopes by employing lower NA objectives.

A surprising role for uric acid: the inflammatory malaria response

Malaria, which is caused by Plasmodium parasite erythrocyte infection, is a highly inflammatory disease with characteristic periodic fevers caused by the synchronous rupture of infected erythrocytes to release daughter parasites. Despite the importance of inflammation in the pathology and mortality induced by malaria, the parasite-derived factors inducing the inflammatory response are still not well characterized. Uric acid is emerging as a central inflammatory molecule in malaria. Not only is uric acid found in the precipitated form in infected erythrocytes, but high concentrations of hypoxanthine, a precursor for uric acid, also accumulate in infected erythrocytes. Both are released upon infected erythrocyte rupture into the circulation where hypoxanthine would be converted into uric acid and precipitated uric acid would encounter immune cells. Uric acid is an important contributor to inflammatory cytokine secretion, dendritic cell and T cell responses induced by Plasmodium, suggesting uric acid as a novel molecular target for anti-inflammatory therapies in malaria.

Clec12a is an inhibitory receptor for uric acid crystals that regulates inflammation in response to cell death

Recognition of cell death by the innate immune system triggers inflammatory responses. However, how these reactions are regulated is not well understood. Here, we identify the inhibitory C-type lectin receptor Clec12a as a specific receptor for dead cells. Both human and mouse Clec12a could physically sense uric acid crystals (monosodium urate, MSU), which are key danger signals for cell-death-induced immunity. Clec12a inhibited inflammatory responses to MSU in vitro, and Clec12a-deficient mice exhibited hyperinflammatory responses after being challenged with MSU or necrotic cells and after radiation-induced thymocyte killing in vivo. Thus, we identified a negative regulatory MSU receptor that controls noninfectious inflammation in response to cell death that has implications for autoimmunity and inflammatory disease.

Dual engagement of the NLRP3 and AIM2 inflammasomes by plasmodium-derived hemozoin and DNA during malaria

Hemozoin (Hz) is the crystalline detoxification product of hemoglobin in Plasmodium-infected erythrocytes. We previously proposed that Hz can carry plasmodial DNA into a subcellular compartment that is accessible to Toll-like receptor 9 (TLR9), inducing an inflammatory signal. Hz also activates the NLRP3 inflammasome in primed cells. We found that Hz appears to colocalize with DNA in infected erythrocytes, even before RBC rupture or phagolysosomal digestion. Using synthetic Hz coated in vitro with plasmodial genomic DNA (gDNA) or CpG oligodeoxynucleotides, we observed that DNA-complexed Hz induced TLR9 translocation, providing a priming and an activation signal for inflammasomes. After phagocytosis, Hz and DNA dissociate. Hz subsequently induces phagolysosomal destabilization, allowing phagolysosomal contents access to the cytosol, where DNA receptors become activated. Similar observations were made with Plasmodium-infected RBCs. Finally, infected erythrocytes activated both the NLRP3 and AIM2 inflammasomes. These observations suggest that Hz and DNA work together to induce systemic inflammation during malaria.

Immunopathological effects of malaria pigment or hemozoin and other crystals

Blood-stage malaria parasites produce insoluble hemozoin (Hz) crystals that are released in the blood circulation upon schizont rupture. In general, endogenous crystal formation or inhalation of crystalline materials is often associated with pathology. As the immune system responds differently to crystalline particles than to soluble molecules, in this review, the properties, immunological recognition, and pathogenic responses of Hz are discussed, and compared with two other major pathogenic crystals, monosodium urate (MSU) and asbestos. Because of the size and shape of MSU crystals and asbestos fibers, phagolysosomal formation is inefficient and often results in leakage of lysosomal content in the cell cytoplasm and/or in the extracellular environment with subsequent cell damage and cell death. Phagolysosomal formation after Hz ingestion is normal, but Hz remains stored inside these cells for months or even longer without any detectable degradation. Nonetheless, the different types of crystals are recognized by similar immune receptors, involving Toll-like receptors, the inflammasome, antibodies, and/or complement factors, and through similar signaling cascades, they activate both proinflammatory and anti-inflammatory immune responses that contribute to inflammation-associated pathology.

Inflammatory Flt3l is essential to mobilize dendritic cells and for T cell responses during Plasmodium infection

Innate sensing mechanisms trigger a variety of humoral and cellular events that are essential to adaptive immune responses. Here we describe an innate sensing pathway triggered by Plasmodium infection that regulates dendritic cell homeostasis and adaptive immunity through Flt3 ligand (Flt3l) release. Plasmodium-induced Flt3l release in mice requires Toll-like receptor (TLR) activation and type I interferon (IFN) production. We found that type I IFN supports the upregulation of xanthine dehydrogenase, which metabolizes the xanthine accumulating in infected erythrocytes to uric acid. Uric acid crystals trigger mast cells to release soluble Flt3l from a pre-synthesized membrane-associated precursor. During infection, Flt3l preferentially stimulates expansion of the CD8-α(+) dendritic cell subset or its BDCA3(+) human dendritic cell equivalent and has a substantial impact on the magnitude of T cell activation, mostly in the CD8(+) compartment. Our findings highlight a new mechanism that regulates dendritic cell homeostasis and T cell responses to infection.