Experimental erythrocytic malaria infection induces elevated serum amyloid P production in mice

Complementary Roles of Short and Long Pentraxins in the Complement-Mediated Immune Response to Aspergillus fumigatus Infections

The ubiquitous mold Aspergillus fumigatus is the major etiologic agent of invasive aspergillosis, a life-threatening infection amongst immune compromised individuals. An increasing body of evidence indicates that effective disposal of A. fumigatus requires the coordinate action of both cellular and humoral components of the innate immune system. Early recognition of the fungal pathogen, in particular, is mediated by a set of diverse soluble pattern recognition molecules (PRMs) that act as "ancestral antibodies" inasmuch as they are endowed with opsonic, pro-phagocytic and killing properties. Pivotal is, in this respect, the contribution of the complement system, which functionally cooperates with cell-borne pattern recognition receptors (PRRs) and other soluble PRMs, including pentraxins. Indeed, complement and pentraxins form an integrated system with crosstalk, synergism, and regulation, which stands as a paradigm of the interplay between PRMs in the mounting and orchestration of antifungal immunity. Following upon our past experience with the long pentraxin PTX3, a well-established immune effector in the host response to A. fumigatus, we recently reported that this fungal pathogen is targeted in vitro and in vivo by the short pentraxin Serum Amyloid P component (SAP) too. Similar to PTX3, SAP promotes phagocytosis and disposal of the fungal pathogen via complement-dependent pathways. However, the two proteins exploit different mechanisms of complement activation and receptor-mediated phagocytosis, which further extends complexity and integration of the complement-pentraxin crosstalk in the immune response to A. fumigatus. Here we revisit this crosstalk in light of the emerging roles of SAP as a novel PRM with antifungal activity.

Serum amyloid P component is an essential element of resistance against Aspergillus fumigatus

Serum amyloid P component (SAP, also known as Pentraxin 2; APCS gene) is a component of the humoral arm of innate immunity involved in resistance to bacterial infection and regulation of tissue remodeling. Here we investigate the role of SAP in antifungal resistance. Apcs^-/- mice show enhanced susceptibility to A. fumigatus infection. Murine and human SAP bound conidia, activate the complement cascade and enhance phagocytosis by neutrophils. Apcs^-/- mice are defective in vivo in terms of recruitment of neutrophils and phagocytosis in the lungs. Opsonic activity of SAP is dependent on the classical pathway of complement activation. In immunosuppressed mice, SAP administration protects hosts against A. fumigatus infection and death. In the context of a study of hematopoietic stem-cell transplantation, genetic variation in the human APCS gene is associated with susceptibility to invasive pulmonary aspergillosis. Thus, SAP is a fluid phase pattern recognition molecule essential for resistance against A. fumigatus.

Tracking acute phase protein response during acute and chronic Toxoplasma gondii infection

Toxoplasmosis is a disease caused by the protozoan Toxoplasma gondii, which occurs worldwide in mammals and birds. Brain is the primary target organ because Toxoplasma gondii is a ubiquitous intracellular parasite that causes most frequently life-threatening encephalitis in immunocompromised patients. Relation of tissue cysts number, histopathology score and acute phase proteins were investigated. In this study, 36 mice are infected with Me49 strain of Toxoplasma gondii. The control group has 6 healthy mice. After inoculation of Toxoplasma gondii, at 10., 15., 20., 30., 45., 60. days, 6 each mice euthanized after collection of blood samples. Hemopexin, haptoglobulin, macroglobulin, serum amyloid A and clusterin levels are determined by ELISA. Then, brain tissues were investigated histopathologically and lesions were scored. The average cyst numbers were determined by counting three samples (25 μl each) of each brain homogenate under light microscopy. Inflammatory reaction was observed on day 10 days after inoculation (d.a.i.) The lesions were characterized by perivascular mononuclear cell infiltration, focal mononuclear cell infiltration in the meninges, and glial proliferation. Tissue cysts were observed in all Toxoplasma gondii-infected groups. The highest lesion score was observed at 60 d.a.i. And the most tissue cyst number were on day 30. d.a.i. Serum levels of hemopexin, haptoglobulin, macroglobulin, serum amyloid A and clusterin were significantly higher than the control group on day 10-20., 10., 10-30., 10.,10-45 d.a.i., respectively. High level of acute phase proteins in mice on certain days infected with Toxoplasma gondii was exhibited a relationship between brain lesions and tissue cysts.

Proteomic analysis of Plasmodium falciparum induced alterations in humans from different endemic regions of India to decipher malaria pathogenesis and identify surrogate markers of severity

India significantly contributes to the global malaria burden and has the largest population in the world at risk of malaria. This study aims to analyze alterations in the human serum proteome as a consequence of non-severe and severe infections by the malaria parasite Plasmodium falciparum to identify markers related to disease severity and to obtain mechanistic insights about disease pathogenesis and host immune responses. In discovery phase of the study, a comprehensive quantitative proteomic analysis was performed using gel-based (2D-DIGE) and gel-free (iTRAQ) techniques on two independent mass spectrometry platforms (ESI-Q-TOF and Q-Exactive mass spectrometry), and selected targets were validated by ELISA. Proteins showing altered serum abundance in falciparum malaria patients revealed the modulation of different physiological pathways including chemokine and cytokine signaling, IL-12 signaling and production in macrophages, complement cascades, blood coagulation, and protein ubiquitination pathways. Some muscle related and cytoskeletal proteins such as titin and galectin-3-binding protein were found to be up-regulated in severe malaria patients. Hemoglobin levels and platelet counts were also found to be drastically lower in severe malaria patients. Identified proteins including serum amyloid A, C-reactive protein, apolipoprotein E and haptoglobin, which exhibited sequential alterations in their serum abundance in different severity levels of malaria, could serve as potential predictive markers for disease severity. To the best of our information, we report here the first comprehensive analysis describing the serum proteomic alterations observed in severe P. falciparum infected patients from different malaria endemic regions of India. This article is part of a Special Issue entitled: Proteomics in India.

Liver-inherent immune system: its role in blood-stage malaria

The liver is well known as that organ which is obligately required for the intrahepatocyte development of the pre-erythrocytic stages of the malaria-causative agent Plasmodium. However, largely neglected is the fact that the liver is also a central player of the host defense against the morbidity- and mortality-causing blood stages of the malaria parasites. Indeed, the liver is equipped with a unique immune system that acts locally, however, with systemic impact. Its main “antipodal” functions are to recognize and to generate effective immunoreactivity against pathogens on the one hand, and to generate tolerance to avoid immunoreactivity with “self” and harmless substances as dietary compounds on the other hand. This review provides an introductory survey of the liver-inherent immune system: its pathogen recognition receptors including Toll-like receptors (TLRs) and its major cell constituents with their different facilities to fight and eliminate pathogens. Then, evidence is presented that the liver is also an essential organ to overcome blood-stage malaria. Finally, we discuss effector responses of the liver-inherent immune system directed against blood-stage malaria: activation of TLRs, acute phase response, phagocytic activity, cytokine-mediated pro- and anti-inflammatory responses, generation of “protective” autoimmunity by extrathymic T cells and B-1 cells, and T cell-mediated repair of liver injuries mainly produced by malaria-induced overreactions of the liver-inherent immune system.

Efflux transport of serum amyloid P component at the blood-brain barrier

Serum amyloid P component (SAP), a member of the innate immune system, does not penetrate the brain in physiological conditions; however, SAP is a stabilizing component of the amyloid plaques in neurodegenerative diseases. We investigated the cerebrovascular transport of human SAP in animal experiments and in culture blood-brain barrier (BBB) models. After intravenous injection, no SAP could be detected by immunohistochemistry or ELISA in healthy rat brains. Salmonella typhimurium lipopolysaccharide injection increased BBB permeability for SAP and the number of cerebral vessels labeled with fluorescein isothiocyanate (FITC)-SAP in mice. Furthermore, when SAP was injected to the rat hippocampus, a time-dependent decrease in brain concentration was seen demonstrating a rapid SAP efflux transport in vivo. A temperature-dependent bidirectional transport of FITC-SAP was observed in rat brain endothelial monolayers. The permeability coefficient for FITC-SAP was significantly higher in abluminal to luminal (brain to blood) than in the opposite direction. The luminal release of FITC-SAP from loaded endothelial cells was also significantly higher than the abluminal one. Our data indicate the presence of BBB efflux transport mechanisms protecting the brain from SAP penetration. Damaged BBB integrity due to pathological insults may increase brain SAP concentration contributing to development of neurodegenerative diseases.

Platelet induction of the acute-phase response is protective in murine experimental cerebral malaria

Platelets are most recognized as the cellular mediator of thrombosis, but they are increasingly appreciated for their immunomodulatory roles, including responses to Plasmodium infection. Platelet interactions with endothelial cells and leukocytes contribute significantly to the pathogenesis of experimental cerebral malaria (ECM). Recently, it has been suggested that platelets not only have an adverse role in cerebral malaria, but platelets may also be protective in animal models of uncomplicated malaria. We now demonstrate that these diverse and seemingly contradictory roles for platelets extend to cerebral malaria models and are dependent on the timing of platelet activation during infection. Our data show that platelets are activated very early in ECM and have a central role in initiation of the acute-phase response to blood-stage infection. Unlike platelet depletion or inhibition postinfection, preinfection platelet depletion or treatment with a platelet inhibitor is not protective. Additionally, we show that platelet-driven acute-phase responses have a major role in protecting mice from ECM by limiting parasite growth. Our data now suggest that platelets have a complex role in ECM pathogenesis: platelets help limit parasite growth early postinfection, but with continued platelet activation as the disease progresses, platelets contribute to ECM-associated inflammation.

Acute phase proteins in animals

Acute phase proteins (APP) were first identified in the early 1900s as early reactants to infectious disease. They are now understood to be an integral part of the acute phase response (APR) which is the cornerstone of innate immunity. APP have been shown to be valuable biomarkers as increases can occur with inflammation, infection, neoplasia, stress, and trauma. All animals--from fish to mammals--have demonstrable APP, but the type of major APP differs by species. While the primary application of these proteins in a clinical setting is prognostication, studies in animals have demonstrated relevance to diagnosis and detection and monitoring for subclinical disease. APP have been well documented in laboratory, companion, and large animals. With the advent of standardized and automated assays, these biomarkers are available for use in all fields of veterinary medicine as well as basic and clinical research.

Serum proteome analysis of vivax malaria: An insight into the disease pathogenesis and host immune response

Vivax malaria is the most widely distributed human malaria resulting in 80-300 million clinical cases every year. It causes severe infection and mortality but is generally regarded as a benign disease and has not been investigated in detail. The present study aimed to perform human serum proteome analysis in a malaria endemic area in India to identify potential serum biomarkers for vivax malaria and understand host response. The proteomic analysis was performed on 16 age and gender matched subjects (vivax patients and control) in duplicate. Protein extraction protocols were optimized for large coverage of the serum proteome and to obtain high-resolution data. Identification of 67 differentially expressed and statistically significant (Student's t-test; p<0.05) protein spots was established by MALDI-TOF/TOF mass spectrometry. Many of the identified proteins such as apolipoprotein A and E, serum amyloid A and P, haptoglobin, ceruloplasmin, and hemopexin are interesting from a diagnostic point of view and could further be studied as potential serum biomarkers. The differentially expressed serum proteins in vivax malaria identified in this study were subjected to functional pathway analysis using multiple software, including Ingenuity Pathway Analysis (IPA), Protein ANalysis THrough Evolutionary Relationships (PANTHER) and Database for Annotation, Visualization and Integrated Discovery (DAVID) functional annotation tool for better understanding of the biological context of the identified proteins, their involvement in various physiological pathways and association with disease pathogenesis. Functional pathway analysis of the differentially expressed proteins suggested the modulation of multiple vital physiological pathways, including acute phase response signaling, complement and coagulation cascades, hemostasis and vitamin D metabolism pathway due to this parasitic infection. This article is part of a Special Issue entitled: Proteomics: The clinical link.

Serum amyloid P aids complement-mediated immunity to Streptococcus pneumoniae

The physiological functions of the acute phase protein serum amyloid P (SAP) component are not well defined, although they are likely to be important, as no natural state of SAP deficiency has been reported. We have investigated the role of SAP for innate immunity to the important human pathogen Streptococcus pneumoniae. Using flow cytometry assays, we show that SAP binds to S. pneumoniae, increases classical pathway–dependent deposition of complement on the bacteria, and improves the efficiency of phagocytosis. As a consequence, in mouse models of infection, mice genetically engineered to be SAP-deficient had an impaired early inflammatory response to S. pneumoniae pneumonia and were unable to control bacterial replication, leading to the rapid development of fatal infection. Complement deposition, phagocytosis, and control of S. pneumoniae pneumonia were all improved by complementation with human SAP. These results demonstrate a novel and physiologically significant role for SAP for complement-mediated immunity against an important bacterial pathogen, and provide further evidence for the importance of the classical complement pathway for innate immunity.

Serum amyloid P (SAP) is a protein that is found in high concentrations in the blood, the exact function(s) of which are not clear. However, no known natural state of SAP deficiency has been identified, which suggests that SAP does have a vital role in human health. SAP can bind to molecular patterns found on the surface of bacteria, and it has been proposed that this may mark bacteria for attack by the immune system. We have investigated whether SAP helps protect against an important bacterial pathogen, Streptococcus pneumoniae. We show that SAP binds to different strains of S. pneumoniae, and that this leads to activation of an important component of the immune response called the complement system. Complement is particularly important for defence against S. pneumoniae infections, and using animal models of infection, we demonstrate that loss of SAP makes mice more susceptible to S. pneumoniae pneumonia. These results suggest that SAP helps the immune system to recognise invasion by bacteria and describe a new mechanism required for control of S. pneumoniae infections. This study may help the design of new therapeutic strategies to prevent or treat important bacterial diseases.

Serum amyloid P-component in murine tuberculosis: induction kinetics and intramacrophage Mycobacterium tuberculosis growth inhibition in vitro

Serum amyloid P-component (SAP), a pentraxin, is known to play an important role in innate immunity to microbial infections; however, nothing is known about it during tuberculosis (TB). Mice intratracheally infected with Mycobacterium tuberculosis Erdman, showed peak SAP levels (442+/-58.2 microg/ml) on day 21, which declined to background levels by day 60. Their serum interleukin-6 levels paralleled SAP levels, whereas, their serum transforming growth factor-beta levels were paradoxical. During the acute phase of infection, the SAP levels positively correlated with the lung mycobacterial load. Purified mouse SAP (1-50 microg/ml) treatment of M. tuberculosis-infected alveolar macrophages (AMs), in vitro, inhibited their intracellular mycobacterial growth; maximum inhibition (1.1 log10 CFU reduction) occurred at 10 microg/ml, and a 4-day treatment appeared optimal. Treatment of AMs with both rabbit anti-mouse SAP polyclonal antibody and mannose-derived simple sugars, separately, blocked the SAP-induced inhibition of mycobacterial growth. The mycobacterial growth inhibition appeared to be nitric oxide (NO)-dependent as NO synthase inhibitors, both aminoguanidine and N(G)-monomethyl-L-arginine, annulled it. Further, SAP treatment of infected AMs induced significant (P<0.05) elaboration of nitrite (72.1+/-8.3 nM/ml), compared to the controls, and these AMs showed augmented expression of inducible NO synthase. This first study demonstrates that during murine TB the SAP levels were increased, and purified mouse SAP inhibited the intra-AM M. tuberculosis growth, in vitro, apparently via NO-dependent mechanism(s). SAP may thus contribute both to the pathogenesis and pulmonary innate immunity in TB.

Acute-phase reactants during murine tuberculosis: Unknown dimensions and new frontiers

SETTING

Serum amyloid P-component (SAP) plays important roles in host defense during various infectious diseases; however, nothing is known in tuberculosis (TB).

OBJECTIVE

To study the SAP response of Mycobacterium tuberculosis H37Rv- and H37Ra-infected mice, and to determine the effect(s) of purified mouse SAP both on their intra-alveolar macrophage (AM) uptake and intra-AM growth in vitro.

DESIGN

The SAP levels of mice intratracheally infected with M. tuberculosis H37Rv and H37Ra were determined by ELISA. Mycobacterial AM uptake and intra-AM growth in vitro were determined using fluorescence microscopy and plating, respectively.

RESULTS

M. tuberculosis H37Rv-infected mice showed significantly (p < 0.05) increased SAP levels (352.8+/-36.1 microg/ml) with compared mice infected with M. tuberculosis H37Ra (170+/-18.5 microg/ml). During the acute phase of both these infections, enhanced SAP levels correlated with the lung mycobacterial load. In vitro, purified mouse SAP (1-80 microg/ml) inhibited the AM uptake of both the mycobacteria in a concentration-dependent manners to a similar extent; 20 microg/ml SAP appeared optimal. Mycobacterial uptake inhibition was divalent cation- and pH-dependent, and was unaffected both by heat-inactivated and deglycosylated SAP, separately. Curiously, purified mouse SAP (1-80 microg/ml), in a concentration-dependent manner, inhibited the intra-AM growth of both M. tuberculosis H37Rv and H37Ra in vitro; the effect was 0.8 log10 CFUs greater on the latter. Both the mannose-based simple sugars and rabbit anti-mouse SAP polyclonal antibody, separately, annulled the inhibition of mycobacterial growth in vitro.

CONCLUSION

This initial study demonstrates that both the SAP response of M. tuberculosis-infected mice, and the SAP-induced intra-AM mycobacterial growth inhibition in vitro were apparently dependent on mycobacterial virulence.

Parasite-specific IgM plays a significant role in the protective immune response to asexual erythrocytic stage Plasmodium chabaudi AS infection

A comparison of Plasmodium chabaudi AS infection in BALB/c and BALB/c IgM-deficient mice demonstrated a protective role for IgM during infection. IgM-/- mice, unlike microMT mice, display competent B cell humoral immune responses. Increased susceptibility of IgM-/- mice was demonstrated by increased mortality, an advanced ascending infection and higher peak parasitaemia, as well as enhanced anaemia and weight loss compared with wild-type mice. The recrudescent parasitaemias were also higher in the IgM-/- mice. Early specific IgM production in P. chabaudi-infected wild-type mice was followed by IgG1 and IgG2a production, while IgG1 and IgG2a production in IgM-/- mice was preceded by specific IgD production. No protective role for natural IgM against P. chabaudi AS infection was detected as passive transfer of naïve WT serum into IgM-/- mice did not alter the disease outcome or reduce parasite numbers. Passive transfer of WT antiserum, containing predominantly specific IgM, into IgM-/- mice delayed the ascending parasitaemia and reduced mortality. Similarly, coating parasitized red blood cells with WT antiserum, but not IgM-/- antisera, prior to infection also slightly delayed the ascending acute parasitaemia. Specific IgM therefore plays an important role in the limitation of parasite replication during asexual erythrocytic P. chabaudi AS infection.

Increase in serum amyloid a evoked by dietary cholesterol is associated with increased atherosclerosis in mice

BACKGROUND

Elevated serum amyloid A (SAA) levels are associated with increased cardiovascular risk. SAA levels can be increased by dietary fat and cholesterol. Moreover, SAA can cause lipoproteins to bind extracellular vascular proteoglycans, a process that is critical in atherogenesis. Therefore, we hypothesized that diet-induced increases in SAA would increase atherosclerosis independent of their effect on plasma cholesterol levels.

METHODS AND RESULTS

Female LDL-receptor-null (LDLR-/-) mice were fed high-saturated fat diets (21%, wt/wt), with or without added cholesterol (0.15%, wt/wt), for 10 weeks. Compared with chow-fed controls, the high-fat diets increased plasma SAA levels. Addition of cholesterol further increased SAA levels 2-fold (P<0.05) without further increasing plasma cholesterol levels. Addition of dietary cholesterol also increased atherosclerosis (P<0.05). Four lines of evidence suggest that SAA actually might cause atherosclerosis: (1) SAA levels when mice were euthanized correlated with the extent of atherosclerosis (r=0.49; P<0.02); (2) SAA levels after 5 weeks of diet correlated with the extent of atherosclerosis at 10 weeks (r=0.66; P<0.01); (3) binding of HDL from these animals to proteoglycans in vitro was related to the HDL-SAA content (r=0.65; P<0.01); and (4) immunoreactive SAA was present in lesion areas enriched with both proteoglycans and apolipoprotein A-I, the major HDL apolipoprotein.

CONCLUSIONS

Addition of cholesterol to a high-fat diet increased plasma SAA levels and atherosclerosis independent of an adverse effect on plasma lipoproteins, consistent with the hypothesis that SAA may promote atherosclerosis directly by mediating retention of SAA-enriched HDL to vascular proteoglycans.