Lipids from attenuated and virulent Babesia bovis strains induce differential TLR2-mediated macrophage activation

The roles of COX-2 in protozoan infection

Protozoan diseases cause great harm in animal husbandry and require human-provided medical treatment. Protozoan infection can induce changes in cyclooxygenase-2 (COX-2) expression. The role played by COX-2 in the response to protozoan infection is complex. COX-2 induces and regulates inflammation by promoting the synthesis of different prostaglandins (PGs), which exhibit a variety of biological activities and participate in pathophysiological processes in the body in a variety of ways. This review explains the roles played by COX-2 in protozoan infection and analyzes the effects of COX-2-related drugs in protozoan diseases.

Congenital Transmission of Apicomplexan Parasites: A Review

Apicomplexans are a group of pathogenic protists that cause various diseases in humans and animals that cause economic losses worldwide. These unicellular eukaryotes are characterized by having a complex life cycle and the ability to evade the immune system of their host organism. Infections caused by some of these parasites affect millions of pregnant women worldwide, leading to various adverse maternal and fetal/placental effects. Unfortunately, the exact pathogenesis of congenital apicomplexan diseases is far from being understood, including the mechanisms of how they cross the placental barrier. In this review, we highlight important aspects of the diseases caused by species of Plasmodium, Babesia, Toxoplasma, and Neospora, their infection during pregnancy, emphasizing the possible role played by the placenta in the host-pathogen interaction.

Innate Immune Response to Tick-Borne Pathogens: Cellular and Molecular Mechanisms Induced in the Hosts

Many pathogens are transmitted by tick bites, including Anaplasma spp., Ehrlichia spp., Rickettsia spp., Babesia and Theileria sensu stricto species. These pathogens cause infectious diseases both in animals and humans. Different types of immune effector mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen-derived antigens or indirectly by molecules released by host cells binding to these antigens. The components of innate immunity, such as natural killer cells, complement proteins, macrophages, dendritic cells and tumor necrosis factor alpha, cause a rapid and intense protection for the acute phase of infectious diseases. Moreover, the onset of a pro-inflammatory state occurs upon the activation of the inflammasome, a protein scaffold with a key-role in host defense mechanism, regulating the action of caspase-1 and the maturation of interleukin-1β and IL-18 into bioactive molecules. During the infection caused by different microbial agents, very similar profiles of the human innate immune response are observed including secretion of IL-1α, IL-8, and IFN-α, and suppression of superoxide dismutase, IL-1Ra and IL-17A release. Innate immunity is activated immediately after the infection and inflammasome-mediated changes in the pro-inflammatory cytokines at systemic and intracellular levels can be detected as early as on days 2–5 after tick bite. The ongoing research field of “inflammasome biology” focuses on the interactions among molecules and cells of innate immune response that could be responsible for triggering a protective adaptive immunity. The knowledge of the innate immunity mechanisms, as well as the new targets of investigation arising by bioinformatics analysis, could lead to the development of new methods of emergency diagnosis and prevention of tick-borne infections.

Involvement of lipids from Leishmania braziliensis promastigotes and amastigotes in macrophage activation

Leishmania are obligate protozoan parasites responsible for substantial public health problems in tropical and subtropical regions around the world, with L. braziliensis being one of the causative agents of American Tegumentary Leishmaniasis. Macrophages, fundamental cells in the innate inflammatory response against Leishmania, constitute a heterogeneous group with multiple activation phenotypes and functions. The outcome of this infection depends largely on the activation status of macrophages, the first line of mammalian defense and the major target cells for parasite replication. The importance of lipids, the major components of cell membranes, goes beyond their basic structural functions. Lipid bioactive molecules have been described in Leishmania spp., and in the recent years the knowledge about the biological relevance of lipids in particular and their relationship with the immune response is expanding. The present work analyzes the biological effects of L. braziliensis lipids from lysed promastigotes (PRO) to mimic rapid modulatory processes that could occur in the initial steps of infection or the effects of lipids from lysed and incubated promastigotes (PROinc), simulating the parasite lipid degradation processes triggered after parasite lysis that might occur in the mammalian host. To perform these studies, lipid profiles of PRO and PROinc were compared with lipids from amastigotes under similar conditions (AMA and AMAinc), and the effect of these lipid extracts were analyzed on the induction of an inflammatory response in murine peritoneal macrophages: LB induction, COX-2, iNOS and Arginase expression, TNF-α, IL-10 and NO production, Arginase activity and M1/M2 markers mRNA induction.

Babesia divergens glycosylphosphatidylinositols modulate blood coagulation and induce Th2-biased cytokine profiles in antigen presenting cells

Glycosylphosphatidylinositols (GPIs) are glycolipids described as toxins of protozoan parasites due to their inflammatory properties in mammalian hosts characterized by the production of interleukin (IL)-1, IL-12 and tumor necrosis factor (TNF)-α. In the present work, we studied the cytokines produced by antigen presenting cells in response to ten different GPI species extracted from Babesia divergens, responsible for babesiosis. Interestingly, B. divergens GPIs induced the production of anti-inflammatory cytokines (IL-2, IL-5) and of the regulatory cytokine IL-10 by macrophages and dendritic cells. In contrast to all protozoan GPIs studied until now, GPIs from B. divergens did not stimulate the production of TNF-α and IL-12, leading to a unique Th1/Th2 profile. Analysis of the carbohydrate composition of the B. divergens GPIs indicated that the di-mannose structure was different from the evolutionary conserved tri-mannose structure, which might explain the particular cytokine profile they induce. Expression of major histocompatibility complex (MHC) molecules on dendritic cells and apoptosis of mouse peritoneal cells were also analysed. B. divergens GPIs did not change expression of MHC class I, but decreased expression of MHC class II at the cell surface, while GPIs slightly increased the percentages of apoptotic cells. During pathogenesis of babesiosis, the inflammation-coagulation auto-amplification loop can lead to thrombosis and the effect of GPIs on coagulation parameters was investigated. Incubation of B. divergens GPIs with rat plasma ex vivo led to increase of fibrinogen levels and to prolonged activated partial thromboplastin time, suggesting a direct modulation of the extrinsic coagulation pathway by GPIs.

Lipids From Trypanosoma cruzi Amastigotes of RA and K98 Strains Generate a Pro-inflammatory Response via TLR2/6

Lipids from microorganisms are ligands of Toll like receptors (TLRs) and modulate the innate immune response. Herein, we analyze in vitro the effect of total lipid extracts from Trypanosoma cruzi amastigotes of RA and K98 strains (with polar biological behavior) on the induction of the inflammatory response and the involvement of TLRs in this process. We demonstrated that total lipid extracts from both strains induced lipid body formation, cyclooxygenase-2 expression and TNF-α and nitric oxide release in macrophages, as well as NF-κB activation and IL-8 release in HEK cells specifically through a TLR2/6 dependent pathway. We also evaluated the inflammatory response induced by total lipid extracts obtained from lysed parasites that were overnight incubated to allow the action of parasite hydrolytic enzymes, such as Phospholipase A₁, over endogenous phospholipids. After incubation, these total lipid extracts showed a significantly reduced pro-inflammatory response, which could be attributed to the changes in the content of known bioactive lipid molecules like lysophospholipids and fatty acids, here reported. Moreover, analyses of total fatty acids in each lipid extract were performed by gas chromatography-mass spectrometry. Our results indicate a relevant role of T. cruzi lipids in the induction of a pro-inflammatory response through the TLR2/6 pathway that could contribute to the modulation of the immune response and host survival.

Involvement of TLR6 in the induction of COX-2, PGE2 and IL-10 in macrophages by lipids from virulent S2P and attenuated R1A Babesia bovis strains

Toll like receptors (TLRs) are involved in the modulation of diverse host genes expression through a complex network of signalling events that allow for an appropriate response to a microbial pathogen. In the present work we used TLR6KO mice in order to study the role of TLR6 in the immune discrimination of lipids from two Babesia bovis strains, attenuated R1A (LA) and virulent S2P (LV), and the consequent macrophage activation. We demonstrated that TLR6 is required for lipid body induction in murine peritoneal macrophages by both LA and LV. Interestingly, as regards IL-10 and COX-2/PGE2 pathway induction by LA and LV, we observed differences in the biological effects produced by these lipid extracts. Our results indicate a role of TLR6 in the down-modulation of these immunoregulators only in the case of LA, whereas this receptor was not implicated in pro-inflammatory TNFα, IL-6 and KC release induced by LA. Remarkably, LV did not exert the down-modulatory effect observed for LA, supporting the notion that LA and LV possess different lipid composition that could correlate with the polar pathogenic effect of both B. bovis strains.

Vaccines against bovine babesiosis: where we are now and possible roads ahead

SUMMARY Bovine babesiosis caused by the tick-transmitted haemoprotozoans Babesia bovis, Babesia bigemina and Babesia divergens commonly results in substantial cattle morbidity and mortality in vast world areas. Although existing live vaccines confer protection, they have considerable disadvantages. Therefore, particularly in countries where large numbers of cattle are at risk, important research is directed towards improved vaccination strategies. Here a comprehensive overview of currently used live vaccines and of the status quo of experimental vaccine trials is presented. In addition, pertinent research fields potentially contributing to the development of novel non-live and/or live vaccines are discussed, including parasite antigens involved in host cell invasion and in pathogen-tick interactions, as well as the protective immunity against infection. The mining of available parasite genomes is continuously enlarging the array of potential vaccine candidates and, additionally, the recent development of a transfection tool for Babesia can significantly contribute to vaccine design. However, the complication and high cost of vaccination trials hinder Babesia vaccine research, and have so far seriously limited the systematic examination of antigen candidates and prevented an in-depth testing of formulations using different immunomodulators and antigen delivery systems.

Babesia bovis:lipids from virulent S2P and attenuated R1A strains trigger differential signalling and inflammatory responses in bovine macrophages

The intra-erythrocytic protozoanBabesia bovisis an economically important pathogen that causes an acute and often fatal infection in adult cattle. Babesiosis limitation depends on the early activation of macrophages, essential cells of the host innate immunity, which can generate an inflammatory response mediated by cytokines and nitric oxide (NO). Herein, we demonstrate in bovine macrophages that lipids fromB. bovisattenuated R1A strain (LA) produced a stronger NO release, an early TNFαmRNA induction and 2-fold higher IL-12p35 mRNA levels compared to the lipids of virulent S2P strain (LV). Neither LAnor LVinduced anti-inflammatory IL-10. Regarding signalling pathways, we here report that LAinduced a significant phosphorylation of p38 and extracellular signal-regulated kinases 1 and 2 (ERK1/2) whereas LVonly induced a reduced activation of ERK1/2. Besides, NF-κB was activated by LAand LV, but LAproduced an early degradation of the inhibitor IκB. Interestingly, LVand the majority of its lipid fractions, exerted a significant inhibition of concanavalin A-induced peripheral blood mononuclear cell proliferation with respect to LAand its corresponding lipid fractions. In addition, we determined that animals infected with R1A developed a higher increase in IgM anti-phosphatidylcholine than those inoculated with S2P. Collectively, S2P lipids generated a decreased inflammatory response contributing to the evasion of innate immunity. Moreover, since R1A lipids induced a pro-inflammatory profile, we propose these molecules as good candidates for immunoprophylactic strategies against babesiosis.

A novel function of MUC18: amplification of lung inflammation during bacterial infection

Bacterial infection plays a critical role in exacerbations of various lung diseases, including chronic pulmonary obstructive disease (COPD) and asthma. Excessive lung inflammation is a prominent feature in disease exacerbations, but the underlying mechanisms remain poorly understood. Cell surface glycoprotein MUC18 (alias CD146 or melanoma cell adhesion molecule) has been shown to promote metastasis in several tumors, including melanoma. We explored the function of MUC18 in lung inflammatory responses to bacteria (eg, Mycoplasma pneumoniae) involved in lung disease exacerbations. MUC18 expression was increased in alveolar macrophages from lungs of COPD and asthma patients, compared with normal healthy human subjects. Mouse alveolar macrophages also express MUC18. After M. pneumoniae lung infection, Muc18(-/-) mice exhibited lower levels of the lung proinflammatory cytokines KC and TNF-α and less neutrophil recruitment than Muc18(+/+) mice. Alveolar macrophages from Muc18(-/-) mice produced less KC than those from Muc18(+/+) mice. In Muc18(-/-) mouse alveolar macrophages, adenovirus-mediated MUC18 gene transfer increased KC production. MUC18 amplified proinflammatory responses in alveolar macrophages, in part through enhancing the activation of nuclear factor-κB (NF-κB). Our results demonstrate, for the first time, that MUC18 exerts a proinflammatory function during lung bacterial infection. Up-regulated MUC18 expression in lungs (eg, in alveolar macrophages) of COPD and asthma patients may contribute to excessive inflammation during disease exacerbations.

Phospholipases a in trypanosomatids

Phospholipases are a complex and important group of enzymes widespread in nature, that play crucial roles in diverse biochemical processes and are classified as A₁, A₂, C, and D. Phospholipases A₁ and A₂ activities have been linked to pathogenesis in various microorganisms, and particularly in pathogenic protozoa they have been implicated in cell invasion. Kinetoplastids are a group of flagellated protozoa, including extra- and intracellular parasites that cause severe disease in humans and animals. In the present paper, we will mainly focus on the three most important kinetoplastid human pathogens, Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp., giving a perspective of the research done up to now regarding biochemical, biological, and molecular characteristics of Phospholipases A₁ and A₂ and their contribution to pathogenesis.