Serum amyloid A protein in acute viral infections

The utility of serum amyloid A and other acute-phase reactants determination in ambulatory care COVID-19 patients

Background

The unpredictable course of Coronavirus Disease 19 (COVID-19) is making good severity assessment tools crucial. This study aimed to assess the usefulness of serum amyloid A (SAA) and other acute-phase reactants (APRs) in ambulatory care COVID-19 patients and identified relationships between these markers and disease outcomes.

Methods

From August to November 2020, patients seen in the outpatient department of the Clinic for Infectious and Tropical Diseases (Belgrade, Serbia) with confirmed COVID-19 were included. Patients were classified into mild, moderate, and severe disease groups based on World Health Organization criteria. SAA, C-reactive protein (CRP), interleukin-6 (IL-6), procalcitonin (PCT), ferritin, fibrinogen, D-dimer, albumin, and transferrin were measured. The median values of all APRs were compared between COVID-19 severity groups, hospitalized and non-hospitalized patients, and survivors and non-survivors. The Receiver operator characteristic (ROC) curve analysis was used for the classification characteristics assessment of individual APRs for the severity of illness, hospitalization, and survival.

Serum amyloid A and metabolic disease: evidence for a critical role in chronic inflammatory conditions

Serum amyloid A (SAA) subtypes 1-3 are well-described acute phase reactants that are elevated in acute inflammatory conditions such as infection, tissue injury, and trauma, while SAA4 is constitutively expressed. SAA subtypes also have been implicated as playing roles in chronic metabolic diseases including obesity, diabetes, and cardiovascular disease, and possibly in autoimmune diseases such as systemic lupus erythematosis, rheumatoid arthritis, and inflammatory bowel disease. Distinctions between the expression kinetics of SAA in acute inflammatory responses and chronic disease states suggest the potential for differentiating SAA functions. Although circulating SAA levels can rise up to 1,000-fold during an acute inflammatory event, elevations are more modest (∼5-fold) in chronic metabolic conditions. The majority of acute-phase SAA derives from the liver, while in chronic inflammatory conditions SAA also derives from adipose tissue, the intestine, and elsewhere. In this review, roles for SAA subtypes in chronic metabolic disease states are contrasted to current knowledge about acute phase SAA. Investigations show distinct differences between SAA expression and function in human and animal models of metabolic disease, as well as sexual dimorphism of SAA subtype responses.

Amyloidogenesis: What Do We Know So Far?

The study of protein aggregation, and amyloidosis in particular, has gained considerable interest in recent times. Several neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) show a characteristic buildup of proteinaceous aggregates in several organs, especially the brain. Despite the enormous upsurge in research articles in this arena, it would not be incorrect to say that we still lack a crystal-clear idea surrounding these notorious aggregates. In this review, we attempt to present a holistic picture on protein aggregation and amyloids in particular. Using a chronological order of discoveries, we present the case of amyloids right from the onset of their discovery, various biophysical techniques, including analysis of the structure, the mechanisms and kinetics of the formation of amyloids. We have discussed important questions on whether aggregation and amyloidosis are restricted to a subset of specific proteins or more broadly influenced by the biophysiochemical and cellular environment. The therapeutic strategies and the significant failure rate of drugs in clinical trials pertaining to these neurodegenerative diseases have been also discussed at length. At a time when the COVID-19 pandemic has hit the globe hard, the review also discusses the plausibility of the far-reaching consequences posed by the virus, such as triggering early onset of amyloidosis. Finally, the application(s) of amyloids as useful biomaterials has also been discussed briefly in this review.

Acute Inflammation Is a Predisposing Factor for Weight Gain and Insulin Resistance

In the course of infection and intense endotoxemia processes, induction of a catabolic state leading to weight loss is observed in mice and humans. However, the late effects of acute inflammation on energy homeostasis, regulation of body weight and glucose metabolism are yet to be elucidated. Here, we addressed whether serial intense endotoxemia, characterized by an acute phase response and weight loss, could be an aggravating or predisposing factor to weight gain and associated metabolic complications. Male Swiss Webster mice were submitted to 8 consecutive doses of lipopolysaccharide (10 mg/kg LPS), followed by 10 weeks on a high-fat diet (HFD). LPS-treated mice did not show changes in weight when fed standard chow. However, when challenged by a high-fat diet, LPS-treated mice showed greater weight gain, with larger fat depot areas, increased serum leptin and insulin levels and impaired insulin sensitivity when compared to mice on HFD only. Acute endotoxemia caused a long-lasting increase in mRNA expression of inflammatory markers such as TLR-4, CD14 and serum amyloid A (SAA) in the adipose tissue, which may represent the key factors connecting inflammation to increased susceptibility to weight gain and impaired glucose homeostasis. In an independent experimental model, and using publicly available microarray data from adipose tissue from mice infected with Gram-negative bacteria, we performed gene set enrichment analysis and confirmed upregulation of a set of genes responsible for cell proliferation and inflammation, including TLR-4 and SAA. Together, we showed that conditions leading to intense and recurring endotoxemia, such as common childhood bacterial infections, may resound for a long time and aggravate the effects of a western diet. If confirmed in humans, infections should be considered an additional factor contributing to obesity and type 2 diabetes epidemics.

Automated machine learning optimizes and accelerates predictive modeling from COVID-19 high throughput datasets

COVID-19 outbreak brings intense pressure on healthcare systems, with an urgent demand for effective diagnostic, prognostic and therapeutic procedures. Here, we employed Automated Machine Learning (AutoML) to analyze three publicly available high throughput COVID-19 datasets, including proteomic, metabolomic and transcriptomic measurements. Pathway analysis of the selected features was also performed. Analysis of a combined proteomic and metabolomic dataset led to 10 equivalent signatures of two features each, with AUC 0.840 (CI 0.723-0.941) in discriminating severe from non-severe COVID-19 patients. A transcriptomic dataset led to two equivalent signatures of eight features each, with AUC 0.914 (CI 0.865-0.955) in identifying COVID-19 patients from those with a different acute respiratory illness. Another transcriptomic dataset led to two equivalent signatures of nine features each, with AUC 0.967 (CI 0.899-0.996) in identifying COVID-19 patients from virus-free individuals. Signature predictive performance remained high upon validation. Multiple new features emerged and pathway analysis revealed biological relevance by implication in Viral mRNA Translation, Interferon gamma signaling and Innate Immune System pathways. In conclusion, AutoML analysis led to multiple biosignatures of high predictive performance, with reduced features and large choice of alternative predictors. These favorable characteristics are eminent for development of cost-effective assays to contribute to better disease management.

The up-to-date pathophysiology of Kawasaki disease

Kawasaki disease (KD) is an acute systemic vasculitis of an unknown aetiology. A small proportion of children exposed to severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) or infected by Yersinia reproducibly develop principal symptoms of KD in various ethnic areas, but not in all studies. These microbes provoke a rapid cell‐damaging process, called ‘pyroptosis’, which is characterised by a subsequent release of proinflammatory cellular components from damaged endothelial and innate immune cells. In agreement with these molecular events, patients with KD show elevated levels of damage‐associated molecular patterns derived from cell death. In addition, an overwhelming amount of oxidative stress‐associated molecules, including oxidised phospholipids or low‐density lipoproteins, are generated as by‐products of inflammation during the acute phase of the disease. These molecules induce abnormalities in the acquired immune system and activate innate immune and vascular cells to produce a range of proinflammatory molecules such as cytokines, chemokines, proteases and reactive oxygen species. These responses further recruit immune cells to the arterial wall, wherein inflammation and oxidative stress closely interact and mutually amplify each other. The inflammasome, a key component of the innate immune system, plays an essential role in the development of vasculitis in KD. Thus, innate immune memory, or ‘trained immunity’, may promote vasculitis in KD. Hence, this review will be helpful in understanding the pathophysiologic pathways leading to the development of principal KD symptoms and coronary artery lesions in patients with KD, as well as in subsets of patients with SARS‐CoV‐2 and Yersinia infections.

Marked Changes in Serum Amyloid A Distribution and High-Density Lipoprotein Structure during Acute Inflammation

High-density lipoprotein- (HDL-) cholesterol measurements are generally used in the diagnosis of cardiovascular diseases. However, HDL is a complicated heterogeneous lipoprotein, and furthermore, it can be converted into dysfunctional forms during pathological conditions including inflammation. Therefore, qualitative analysis of pathophysiologically diversified HDL forms is important. A recent study demonstrated that serum amyloid A (SAA) can remodel HDL and induce atherosclerosis not only over long periods of time, such as during chronic inflammation, but also over shorter periods. However, few studies have investigated rapid HDL remodeling. In this study, we analyzed HDL samples from patients undergoing orthopedic surgery inducing acute inflammation. We enrolled 13 otherwise healthy patients who underwent orthopedic surgery. Plasma samples were obtained on preoperative day and postoperative days (POD) 1-7. SAA, apolipoprotein A-I (apoA-I), and apolipoprotein A-II (apoA-II) levels in the isolated HDL were determined. HDL particle size, surface charge, and SAA and apoA-I distributions were also analyzed. In every patient, plasma SAA levels peaked on POD3. Consistently, the HDL apoA-I : apoA-II ratio markedly decreased at this timepoint. Native-polyacrylamide gel electrophoresis and high-performance liquid chromatography revealed the loss of small HDL particles during acute inflammation. Furthermore, HDL had a decreased negative surface charge on POD3 compared to the other timepoints. All changes observed were SAA-dependent. SAA-dependent rapid changes in HDL size and surface charge were observed after orthopedic surgery. These changes might affect the atheroprotective functions of HDL, and its analysis can be available for the qualitative HDL assessment.

Cytokines and serum amyloid A in the pathogenesis of hepatitis C virus infection

Expression of the acute phase protein serum amyloid A (SAA) is dependent on the release of the pro-inflammatory cytokines IL-1, IL-6 and TNF-α during infection and inflammation. Hepatitis C virus (HCV) upregulates SAA-inducing cytokines. In line with this, a segment of chronically infected individuals display increased circulating levels of SAA. SAA has even been proposed to be a potential biomarker to evaluate treatment efficiency and the course of disease. SAA possesses antiviral activity against HCV via direct interaction with the viral particle, but might also divert infectivity through its function as an apolipoprotein. On the other hand, SAA shares inflammatory and angiogenic activity with chemotactic cytokines by activating the G protein-coupled receptor, formyl peptide receptor 2. These latter properties might promote chronic inflammation and hepatic injury. Indeed, up to 80 % of infected individuals develop chronic disease because they cannot completely clear the infection, due to diversion of the immune response. In this review, we summarize the interconnection between SAA and cytokines in the context of HCV infection and highlight the dual role SAA could play in this disease. Nevertheless, more research is needed to establish whether the balance between those opposing activities can be tilted in favor of the host defense.

Molecular basis for retinol binding by serum amyloid A during infection

Vitamin A is an essential nutrient for immune system development and function. After absorption from the diet, vitamin A is converted to retinol, which is delivered to cells and tissues by retinol-binding proteins. Serum amyloid A (SAA) proteins are retinol-binding proteins that transport retinol specifically during an infection. In this study, we illuminate the molecular details of how SAA proteins bind to retinol. We present the cocrystal structure of mouse SAA3 bound to retinol, which reveals that 3 molecules of SAA3 assemble to form a deep binding pocket that protects retinol, a fat-soluble molecule, from the aqueous environment. Our findings thus provide structural insight into how retinol is transported throughout the body during infection.

Serum amyloid A (SAA) proteins are strongly induced in the liver by systemic infection and in the intestine by bacterial colonization. In infected mice, SAA proteins circulate in association with the vitamin A derivative retinol, suggesting that SAAs transport retinol during infection. Here we illuminate a structural basis for the retinol–SAA interaction. In the bloodstream of infected mice, most SAA is complexed with high-density lipoprotein (HDL). However, we found that the majority of the circulating retinol was associated with the small fraction of SAA proteins that circulate without binding to HDL, thus identifying free SAA as the predominant retinol-binding form in vivo. We then determined the crystal structure of retinol-bound mouse SAA3 at a resolution of 2.2 Å. Retinol-bound SAA3 formed a novel asymmetric trimeric assembly that was generated by the hydrophobic packing of the conserved amphipathic helices α1 and α3. This hydrophobic packing created a retinol-binding pocket in the center of the trimer, which was confirmed by mutagenesis studies. Together, these findings illuminate the molecular basis for retinol transport by SAA proteins during infection.

Acute phase reactant serum amyloid A in inflammation and other diseases

Acute-phase reactant serum amyloid A (A-SAA) plays an important role in acute and chronic inflammation and is used in clinical laboratories as an indicator of inflammation. Although both A-SAA and C-reactive protein (CRP) are acute-phase proteins, the detection of A-SAA is more conclusive than the detection of CRP in patients with viral infections, severe acute pancreatitis, and rejection reactions to kidney transplants. A-SAA has greater clinical diagnostic value in patients who are immunosuppressed, patients with cystic fibrosis who are treated with corticoids, and preterm infants with late-onset sepsis. Nevertheless, for the assessment of the inflammation status and identification of viral infection in other pathologies, such as bacterial infections, the combinatorial use of A-SAA and other acute-phase proteins (APPs), such as CRP and procalcitonin (PCT), can provide more information and sensitivity than the use of any of these proteins alone, and the information generated is important in guiding antibiotic therapy. In addition, A-SAA-associated diseases and the diagnostic value of A-SAA are discussed. However, the relationship between different A-SAA isotypes and their human diseases are mostly derived from research laboratories with limited clinical samples. Thus, further clinical evaluations are necessary to confirm the clinical significance of each A-SAA isotype. Furthermore, the currently available A-SAA assays are based on polyclonal antibodies, which lack isotype specificity and are associated with many inflammatory diseases. Therefore, these assays are usually used in combination with other biomarkers in the clinic.

Serum amyloid A protein in the course of infectious mononucleosis

Background:

Serum amyloid A (SAA) protein is a major acute phase protein. Increased concentrations have been reported in many inflammatory diseases. In bacterial infections, high levels correlate with those of C-reactive protein (CRP). In viral infections, where CRP changes are weaker, SAA is of value for establishing early diagnosis, monitoring the severity, and the evolution of the disease.

Objective:

Evaluation of SAA as a marker for diagnosis of infectious mononucleosis, including severe forms.

Material and methods:

A total of 31 patients with non-complicated and severe, complicated infectious mononucleosis were examined. SAA and CRP were measured by immuniturbidimetric assays at the day of admission and 4.97 ± 1.35 days later.

Results:

SAA increases significantly than those in a control group, without correlation with the etiologic agent. It decreases when full recovery appears. In the subgroup of subjects with complications, we observed significant increased SAA when Epstein-Barr virus /EBV/ was the etiologic agent, in the course of bacterial and viral secondary infection. SAA is higher than CRP in non-complicated group. In cases of bacterial superinfections, both increase simultaneously and treatment have to be adapted. Second, serum sample for CRP is normal in patients without full recovery where SAA stay increased.

Conclusion:

In viral infections, high SAA concentrations are indicative for early diagnosis, severe course of the diseases, effect of the treatment, early recovery, and disease outcome. When SAA and CRP increase simultaneously, bacterial co-infection is suspected, and relevant antibiotic treatments have to be initiated.

Innate immunity related pathogen recognition receptors and chronic hepatitis B infection

Innate immunity consists of several kinds of pathogen recognition receptors (PRRs), which participate in the recognition of pathogens and consequently activation of innate immune system against pathogens. Recently, several investigations reported that PRRs may also play key roles in the induction/stimulation of immune system related complications in microbial infections. Hepatitis B virus (HBV), as the main cause of viral hepatitis in human, can induce several clinical forms of hepatitis B and also might be associated with hepatic complications such as cirrhosis and hepatocellular carcinoma (HCC). Based on the important roles of PRRs in the eradication of microbial infections including viral infections and their related complications, it appears that the molecules may be a main part of immune responses against viral infections including HBV and participate in the HBV related complications. Thus, this review article has brought together information regarding the roles of PRRs in immunity against HBV and its complications.

A Novel Truncated Form of Serum Amyloid A in Kawasaki Disease

Background

Kawasaki disease (KD) is an acute vasculitis in children that can cause coronary artery abnormalities. Its diagnosis is challenging, and many cytokines, chemokines, acute phase reactants, and growth factors have failed evaluation as specific biomarkers to distinguish KD from other febrile illnesses. We performed protein profiling, comparing plasma from children with KD with febrile control (FC) subjects to determine if there were specific proteins or peptides that could distinguish the two clinical states.

Materials and Methods

Plasma from three independent cohorts from the blood of 68 KD and 61 FC subjects was fractionated by anion exchange chromatography, followed by surface-enhanced laser desorption ionization (SELDI) mass spectrometry of the fractions. The mass spectra of KD and FC plasma samples were analyzed for peaks that were statistically significantly different.

Results

A mass spectrometry peak with a mass of 7,860 Da had high intensity in acute KD subjects compared to subacute KD (p = 0.0003) and FC (p = 7.9 x 10⁻¹⁰) subjects. We identified this peak as a novel truncated form of serum amyloid A with N-terminal at Lys-34 of the circulating form and validated its identity using a hybrid mass spectrum immunoassay technique. The truncated form of serum amyloid A was present in plasma of KD subjects when blood was collected in tubes containing protease inhibitors. This peak disappeared when the patients were examined after their symptoms resolved. Intensities of this peptide did not correlate with KD-associated laboratory values or with other mass spectrum peaks from the plasma of these KD subjects.

Conclusions

Using SELDI mass spectrometry, we have discovered a novel truncated form of serum amyloid A that is elevated in the plasma of KD when compared with FC subjects. Future studies will evaluate its relevance as a diagnostic biomarker and its potential role in the pathophysiology of KD.

Research Progress on Infectious Inflammation Markers in Blood

Acute phase protein (APP) is a type of special protein closely related to infection inflammation. In recent years, a large number of studies have shown that multiple positive and negative APPs, including C-reactive protein, serum amyloid A, procalcitonin, haptoglobin, alpha1 acid glycoprotein, ceruloplasmin, fibrinogen, prealbumin, leptin, albumin, and plasma fibronectin, are significantly correlated to infectious inflammation and that this method is more accurate and reliable than somatic cell test, erythrocyte sedimentation rate test, enzyme activity and content change test, and the like. Therefore, APP could be used as an infectious inflammation marker.

Calibration-free concentration analysis of protein biomarkers in human serum using surface plasmon resonance

In complex biological samples such as serum, determination of specific and active concentration of target proteins, independent of a calibration curve, will be valuable in many applications. Calibration-free concentration analysis (CFCA) is a surface plasmon resonance (SPR)-based label-free approach, which calculates active concentration of proteins using their known diffusion coefficient and observed changes in binding rates at different flow rates under diffusion-limited conditions. Here, for the first time we demonstrate the application of CFCA for determining protein biomarker abundance, specifically serum amyloid A (SAA), directly in the serum samples of patients suffering from different infectious and non-infectious diseases. The assay involves preparation of appropriate reaction surfaces by immobilizing antibodies on CM5 chips via amine coupling followed by serum sample preparation and injection over activated and reference surfaces at flow-rates of 5 and 100 μL/min. The system was validated in healthy and diseased (infectious and non-infectious) serum samples by quantifying two different proteins: β2-microglobulin (β2M) and SAA. All concentration assays were performed for nearly 100 serum samples, which showed reliable quantification in unattended runs with high accuracy and sensitivity. The method could detect the serum β2M to as low as 13 ng/mL in 1000-fold serum dilution, indicating the possible utility of this approach to detect low abundance protein biomarkers in body fluids. Applying the CFCA approach, significant difference in serum abundance of SAA was identified in diseased subjects as compared to the healthy controls, which correlated well with our previous proteomic investigations. Estimation of SAA concentration for a subset of healthy and diseased sera was also performed using ELISA, and the trend was observed to be similar in both SPR assay and ELISA. The reproducibility of CFCA in various serum samples made the interpretation of assay simple and reliable. This study illustrates a significant step forward in rapid monitoring of several protein markers in serum samples, with utility in biomarker validation and other therapeutic applications.

Systemic inflammation and residual viraemia in HIV-positive adults on protease inhibitor monotherapy: a cross-sectional study

BACKGROUND

Increased levels of markers of systemic inflammation have been associated with serious non-AIDS events even in patients on fully suppressive antiretroviral therapy. We explored residual viremia and systemic inflammation markers in patients effectively treated with ritonavir-boosted protease inhibitor monotherapy (PImono).

METHODS

HIV-infected adults with persistent HIV-RNA<50 copies/ml and treated with either a) PImono or b) standard triple-drug cART were recruited for this cross-sectional, exploratory study. Plasma samples were tested for high-sensitivity CRP (hsCRP), Serum Amyloid A (SAA), soluble CD14, IL-6, IL-8 and Cytochrome C. HIV-RNA was measured by real-time PCR (detection limit of 10 copies/ml).

RESULTS

81 patients were recruited (31% on PImono). Two out of 25 (8%) and 3 of 56 (5.4%) patients from the PImono and cART groups respectively had detectable HIV-RNA. Significant correlation between SAA and hsCRP was observed (0.804). No difference between groups was found on prevalence of hsCRP>3 mg/l (21% vs 20% in the PImono and cART groups respectively; p=0.577) or SAA>6.4 mg/l (38% vs 22% in the PImono and cART groups respectively; P=0.172). In a univariate analysis IL6 and IL8 levels were associated with SAA>6.4 mg/l (OR=1.74 and 1.46; 95% CI=1.00-3.03 and 1.06-2.01; p=0.051 and 0.02 respectively) and hsCRP>3 mg/l in (OR=2.00 and 1.37; 95% CI=1.09-3.69 and 1.02-1.85; p=0.026 and 0.039 respectively).

CONCLUSIONS

We found no evidence of increased levels of inflammatory biomarkers or higher prevalence of residual viraemia in patients effectively suppressed on PImono as compared with patients on standard cART.

Plasma proteomic analysis of patients infected with H1N1 influenza virus

This study profiled the plasma proteins of patients infected by the 2011 H1N1 influenza virus. Differential protein expression was identified in plasma obtained from noninfected control subjects (n = 15) and H1N1-infected subjects (n = 15). Plasma proteins were separated by a 2DE large gel system and identified by nano-ultra performance LC-MS. Western blot assays were performed to validate proteins. Eight plasma proteins were upregulated and six proteins were downregulated among 3316 plasma proteins in the H1N1-infected group as compared with the control group. Of 14 up- and downregulated proteins, nine plasma proteins were validated by Western blot analysis. Putative protein FAM 157A, leucine-rich alpha 2 glycoprotein, serum amyloid A protein, and dual oxidase 1 showed significant differential expression. The identified plasma proteins could be potential candidates for biomarkers of H1N1 influenza viral infection. Further studies are needed to develop these proteins as diagnostic biomarkers.

Comparison of serum amyloid A and C-reactive protein as diagnostic markers of systemic inflammation in dogs

The diagnostic performance of canine serum amyloid A (SAA) was compared with that of C-reactive protein (CRP) in the detection of systemic inflammation in dogs. Sera from 500 dogs were retrospectively included in the study. C-reactive protein and SAA were measured using validated automated assays. The overlap performance, clinical decision limits, overall diagnostic performance, correlations, and agreement in the clinical classification between these 2 diagnostic markers were compared. Significantly higher concentrations of both proteins were detected in dogs with systemic inflammation (SAA range: 48.75 to > 2700 mg/L; CRP range: 0.4 to 907.4 mg/L) compared to dogs without systemic inflammation (SAA range: 1.06 to 56.4 mg/L; CRP range: 0.07 to 24.7 mg/L). Both proteins were shown to be sensitive and specific markers of systemic inflammation in dogs. Significant correlations and excellent diagnostic agreement were observed between the 2 markers. However, SAA showed a wider range of concentrations and a significantly superior overall diagnostic performance compared with CRP.

Some acute phase reactants and cholesterol levels in serum of patient with Crimean-Congo haemorrhagic fever

The purpose of this study is to determine erythrocyte sedimentation rate (ESR), C - reactive protein (CRP), serum amyloid-A (SAA) and cholesterol levels in patients with Crimean-Congo Hemorrhagic Fever (CCHF) and determine the relationship of these parameters with the severity of disease. By polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) method 40 patients were diagnosed as CCHF and 39 volunteer without any systemic disease whose blood were taken and their serum separated. SAA, CRP and ESR were measured with ELISA, nephelometry and Mix-Rate x100 vital diagnostic device, respectively, in serum samples. High density lipoprotein (HDL), low density lipoprotein (LDL) and total cholesterol levels were determined by using autoanalyzer HDL, LDL and total cholesterol kit (Syncron LX20). Statistically significant difference was determined between patients and controls in terms of the levels of SAA, CRP, HDL, LDL and total cholesterol (p<0.05). However, there was no significant difference between the groups in terms of the levels of ESR. In addition, neither SAA, CRP, ESR nor HDL, LDL and total cholesterol levels varied with the severity of disease in the cases assessed (p>0.05). Using of CRP and SAA together might increase the sensitivity of diagnosis of CCHF infection. However, none of the parameters investigated in this study were found to be a proper marker of the prognosis in CCHF. Cholesterol levels were significantly decreased in patients with CCHF, which was suggested to be associated with the increased serum levels of SAA in the patient group.

S100A12 suppresses pro-inflammatory, but not pro-thrombotic functions of serum amyloid A

S100A12 is elevated in the circulation in patients with chronic inflammatory diseases and recent studies indicate pleiotropic functions. Serum amyloid A induces monocyte cytokines and tissue factor. S100A12 did not stimulate IL-6, IL-8, IL-1β or TNF-α production by human peripheral blood mononuclear cells but low amounts consistently reduced cytokine mRNA and protein levels induced by serum amyloid A, by ∼49% and ∼46%, respectively. However, S100A12 did not affect serum amyloid A-induced monocyte tissue factor. In marked contrast, LPS-induced cytokines or tissue factor were not suppressed by S100A12. S100A12 did not alter cytokine mRNA stability or the cytokine secretory pathway. S100A12 and serum amyloid A did not appear to form complexes and although they may have common receptors, suppression was unlikely via receptor competition. Serum amyloid A induces cytokines via activation of NF-κB and the MAPK pathways. S100A12 reduced serum amyloid A-, but not LPS-induced ERK1/2 phosphorylation to baseline. It did not affect JNK or p38 phosphorylation or the NF-κB pathway. Reduction in ERK1/2 phosphorylation by S100A12 was unlikely due to changes in intracellular reactive oxygen species, Ca²⁺ flux or to recruitment of phosphatases. We suggest that S100A12 may modulate sterile inflammation by blunting pro-inflammatory properties of lipid-poor serum amyloid A deposited in chronic lesions where both proteins are elevated as a consequence of macrophage activation.

The role of humoral innate immunity in hepatitis C virus infection

Infection with Hepatitis C Virus (HCV) causes chronic disease in approximately 80% of cases, resulting in chronic inflammation and cirrhosis. Current treatments are not completely effective, and a vaccine has yet to be developed. Spontaneous resolution of infection is associated with effective host adaptive immunity to HCV, including production of both HCV-specific T cells and neutralizing antibodies. However, the supporting role of soluble innate factors in protection against HCV is less well understood. The innate immune system provides an immediate line of defense against infections, triggering inflammation and playing a critical role in activating adaptive immunity. Innate immunity comprises both cellular and humoral components, the humoral arm consisting of pattern recognition molecules such as complement C1q, collectins and ficolins. These molecules activate the complement cascade, neutralize pathogens, and recruit antigen presenting cells. Here we review the current understanding of anti-viral components of the humoral innate immune system that play a similar role to antibodies, describing their role in immunity to HCV and their potential contribution to HCV pathogenesis.

Increased inducible nitric oxide synthase expression in organs is associated with a higher severity of H5N1 influenza virus infection

Background

The mechanisms of disease severity caused by H5N1 influenza virus infection remain somewhat unclear. Studies have indicated that a high viral load and an associated hyper inflammatory immune response are influential during the onset of infection. This dysregulated inflammatory response with increased levels of free radicals, such as nitric oxide (NO), appears likely to contribute to disease severity. However, enzymes of the nitric oxide synthase (NOS) family such as the inducible form of NOS (iNOS) generate NO, which serves as a potent anti-viral molecule to combat infection in combination with acute phase proteins and cytokines. Nevertheless, excessive production of iNOS and subsequent high levels of NO during H5N1 infection may have negative effects, acting with other damaging oxidants to promote excessive inflammation or induce apoptosis.

Methodology/Principal Findings

There are dramatic differences in the severity of disease between chickens and ducks following H5N1 influenza infection. Chickens show a high level of mortality and associated pathology, whilst ducks show relatively minor symptoms. It is not clear how this varying pathogenicty comes about, although it has been suggested that an overactive inflammatory immune response to infection in the chicken, compared to the duck response, may be to blame for the disparity in observed pathology. In this study, we identify and investigate iNOS gene expression in ducks and chickens during H5N1 influenza infection. Infected chickens show a marked increase in iNOS expression in a wide range of organs. Contrastingly, infected duck tissues have lower levels of tissue related iNOS expression.

Conclusions/Significance

The differences in iNOS expression levels observed between chickens and ducks during H5N1 avian influenza infection may be important in the inflammatory response that contributes to the pathology. Understanding the regulation of iNOS expression and its role during H5N1 influenza infection may provide insights for the development of new therapeutic strategies in the treatment of avian influenza infection.

Clinical evaluation of the measurement of serum procalcitonin: comparative study of procalcitonin and serum amyloid A protein in patients with high and low concentrations of serum C‐reactive protein

Levels of C-reactive protein (CRP) and serum amyloid A protein (SAA) in blood are increased as acute phase proteins in patients with inflammatory conditions. Most of the currently used inflammatory markers, such as erythrocyte sedimentation rate and CRP or SAA levels, are non-specific parameters. By contrast, procalcitonin (PCT) has been reported to be selectively induced by severe infection in systemic inflammatory response syndrome (SIRS) and also in sepsis or multiorgan dysfunction syndrome. PCT expression is induced only slightly, if at all, by viral infections, autoimmune disorders, neoplastic disorders and trauma arising from surgical intervention. Serum PCT and SAA levels were compared in 93 patients with a CRP concentration higher than 100 mg/L and in 26 patients with a CRP concentration lower than 1.5 mg/L. In patients with high levels of CRP, all patients with sepsis and severe bacterial infection showed a significantly increased PCT concentration of more than 1.0 microg/L and it was possible to differentiate between the patients with neoplastic disorders and those with other inflammatory diseases. In patients with low levels of CRP, the PCT concentration was less than 0.3 microg/L and an increased PCT level was not seen in patients with autoimmune disorders or viral and fungal infections. These results suggest that determining the serum PCT level may be useful in the differential diagnosis of severe infection.

Different isoforms of apolipoprotein AI present heterologous post-translational expression in HIV infected patients

Human immunodeficiency virus (HIV) is rapidly becoming a global health concern. Proteomics technology was employed to examine HIV infected plasma samples in an attempt to identify disease-associated proteins. By comparison with normal and HIV positive plasma samples, at least eight proteins were significantly changed in HIV infected plasma. In particular, apolipoprotein AI presents a heterogeneous change in expression level with different isoforms. Apolipoprotein AI could be a useful biomarker for HIV diagnosis.

Does Renal Function Influence Plasma Levels of Advanced Glycation and Oxidation Protein Products in Patients with Chronic Rheumatic Diseases Complicated by Secondary Amyloidosis?

BACKGROUND

The aim of the study was to assess the contribution of carbonyl and oxidative stresses to the development of amyloidosis in patients suffering from chronic rheumatic diseases, and the potential influence of renal function to their concentrations was considered.

METHODS

We investigated 17 patients with chronic rheumatological diseases and histologically proven diagnosis of AA amyloidosis (group AA-RA), 26 patients suffering from rheumatoid arthritis without any signs of AA amyloidosis (group nonAA-RA) and 20 healthy volunteers (Co). In all patients, advanced glycation end products (AGEs), advanced oxidation protein products (AOPP), pregnancy-associated plasma protein A (PAPP-A) and other selected proinflammatory markers were measured.

RESULTS

An increase in serum levels of AOPP and AGEs was found in the AA-RA group in comparison with nonAA-RA patients and also with Co (p < 0.001 for all comparisons). AGEs positively correlated with serum creatinine (r = 0.67, p = 0.004) and negatively with glomerular filtration rate (r = -0.54, p = 0.027). We did not find a correlation between AOPP and any other assessed parameters including proteins and renal parameters. PAPP-A levels were not significantly increased in any group of patients (AA-RA, nonAA-RA) in comparison with Co.

CONCLUSIONS

Increased plasma levels of AGEs and AOPP in the group of patients with AA-RA may have been partly explained by the diminished renal clearance. However, the increase in AOPP levels was higher than what is expected in this degree of renal failure (glomerular filtration rate in the AA-RA group corresponding to chronic kidney disease stage III).

Serum amyloid A (SAA) concentration varies among rheumatoid arthritis patients estimated by SAA/CRP ratio

BACKGROUND

C reactive protein (CRP) and serum amyloid A (SAA) are similarly sensitive indicators of inflammation, but discrepancies are recognized in several disease conditions. SAA levels are generally higher and vary more among individuals. The significance of the SAA/CRP ratio was evaluated in the estimation of SAA.

METHODS

Sera of out-patients with rheumatoid arthritis (RA) and healthy subjects were measured for CRP and SAA cross-sectionally and longitudinally by a highly sensitive latex agglutination turbidimetric immunoassay. The results were classified into four groups according to the CRP concentration, and the SAA/CRP ratios were calculated and evaluated.

RESULTS

In the cross-sectional study, CRP and SAA were shown to correlate significantly in sera of patients with RA, but not in healthy subjects. The SAA/CRP ratios were wide RA patients and tended to decrease in the range and mean values were observed depending on the concentration of CRP. In the longitudinal study, variations of the ratio among individuals were wide, but smaller and similar within individuals. The difference in magnitude of the ratios is due to the difference in SAA concentration.

CONCLUSION

Variations of SAA/CRP ratios were affected by SAA concentrations. The ratio should be checked in the evaluation of SAA.

Serum amyloid A (SAA) protein and high-sensitivity C-reactive protein (hsCRP) in healthy newborn infants and healthy young through elderly adults

AIM

To determine the levels of serum amyloid A (SAA) protein and high-sensitivity C-reactive protein (hsCRP) in different age groups.

METHODS

Serum samples from 70 healthy newborn infants, 80 blood donors and 81 healthy elderly individuals were analysed using a nephelometric method. The 231 samples were grouped as follows: 35 umbilical cords, 35 newborns, 48 young adults, 28 middle-aged adults, and 85 elderly adults.

RESULTS

Serum levels of both SAA and hsCRP were lower in umbilical cords than in the newborns and young, middle-aged and elderly adults (p<0.0001). The SAA and hsCRP levels were comparable in newborns, and young and middle-age adults, but higher in elderly adults (p<0.0001-0.03). SAA (r2=0.159, p<0.0001) and hsCRP (r2=0.059, p<0.0001) were positively correlated with age and to each other (r2=0.385, p<0.0001).

CONCLUSION

Serum levels of SAA and hsCRP in umbilical cord blood are close to the detection limit and lower than in the other age groups investigated. The elderly have generally higher levels than the younger age groups, which require higher decision levels in inflammatory diseases, including infections. In newborns and young and middle-aged adults, the lower decision levels of 10 mg/l for SAA and 5 mg/l for CRP are suggested.

Plasma proteome of severe acute respiratory syndrome analyzed by two-dimensional gel electrophoresis and mass spectrometry

We have investigated the plasma proteome by using 2D gel electrophoresis and MS from patients with severe acute respiratory syndrome (SARS). A complete proteomic analysis was performed on four patients with SARS in different time courses, and a total of 38 differential spots were selected for protein identification. Most of the proteins identified are acute phase proteins, and their presence represents the consequence of serial cascades initiated by SARS-coronavirus infection. There are several proteins that have never been identified in plasma before using 2D gel electrophoresis, among which peroxiredoxin II was chosen for further study by analyzing additional 20 plasma samples from patients with probable and suspected SARS and patients with fever, respectively. The results showed that the level of plasma peroxiredoxin II in patients with SARS is significantly high and could be secreted by T cells. Taken together, our findings indicate that active innate immune responses, along with the oxidation-associated injuries, may play a major role in the pathogenesis of SARS.

The acute-phase protein response to infection in edematous and nonedematous protein-energy malnutrition

BACKGROUND

Immune structure and function are more compromised in edematous protein-energy malnutrition (PEM) than in nonedematous PEM. Whether the positive acute-phase protein (APP) response to infection is affected remains unknown.

OBJECTIVE

We assessed whether children with edematous PEM can mount a general APP response and compared the kinetic mechanisms of the response in children with edematous PEM with those in children with nonedematous PEM.

DESIGN

Plasma C-reactive protein, alpha(1)-acid glycoprotein, alpha(1)-antitrypsin, haptoglobin, and fibrinogen concentrations and the fractional and absolute synthesis rates of alpha(1)-antitrypsin, haptoglobin, and fibrinogen were measured in 14 children with edematous PEM, aged 11.4 +/- 2 mo, and 9 children with nonedematous PEM, aged 10.1 +/- 1.4 mo, at 3 times: approximately 2 d after hospital admission (period 1), when they were malnourished and infected; approximately 8 d after admission (period 2), when they were malnourished but free of infection; and approximately 54 d after admission (period 3), when they had recovered.

RESULTS

Children with edematous and nonedematous PEM had higher plasma concentrations of 4 of 5 APPs in period 1 than in period 3. The magnitude of the difference in concentration and in the rate of synthesis of the individual APPs was less in the children with edematous PEM than in those with nonedematous PEM. The kinetic data show that the characteristics of the APP response were different in the 2 groups.

CONCLUSIONS

These results suggest that severely malnourished children can mount only a partial APP response to the stress of infection and that the magnitude of this response is less in those with edema.

Relative serum amyloid A (SAA) values: the influence of SAA1 genotypes and corticosteroid treatment in Japanese patients with rheumatoid arthritis

OBJECTIVES

(1) To determine whether serum concentration of serum amyloid A (SAA) protein is influenced by the SAA1 allele in Japanese patients with rheumatoid arthritis (RA) as previously shown in a healthy control group; and (2) to analyse what factors, based on such an allelic bias, influence the relative SAA values of those patients.

METHODS

SAA and C reactive protein (CRP) concentrations together with SAA1 genotypes were determined in 316 Japanese patients with RA. The relative SAA values were evaluated as an SAA/CRP ratio.

RESULTS

Comparison of the three SAA1 homozygote groups showed that the SAA/CRP ratio was highest in the 1.5/1.5 group (mean 9.0, p<0.01 v the other two homozygote groups) followed by the 1.3/1.3 group (mean 7.2, NS v the 1.1/1.1 group) and the 1.1/1.1 group (mean 4.0). The SAA/CRP ratio was significantly higher in patients receiving corticosteroids regardless of the presence of allele 1.5. No clear differences in the ratio between patients with or without amyloidosis were found.

CONCLUSION

The SAA1.5 allele and corticosteroid treatment had a positive influence on SAA concentrations in serum. These findings are important when evaluating SAA concentration in inflammatory diseases and when considering the cause or treatment of amyloidosis.

Amyloid precursors and amyloidosis in inflammatory arthritis

Recent data demonstrating the multifunctional role of serum amyloid A (SAA) in the pathogenesis of amyloidosis have yielded important insights into this potentially fatal consequence of chronic inflammation. SAA has been shown to participate in chemotaxis, cellular adhesion, cytokine production, and metalloproteinase secretion and is thus integrally involved in the disease process. In addition to its production by the liver as part of the acute phase response, SAA is also expressed by several pathologic tissues such atherosclerotic plaques, rheumatoid synovitis and in the brains of patients with Alzheimer disease. Its constitutive production in normal tissue suggests a role for SAA in host defense and tissue turnover. Many pathways are involved in the regulation of SAA, and as more becomes known about these, potential therapeutic targets may be identified. However, the prevention of secondary amyloidosis is best achieved by early and adequate treatment of patients with chronic inflammatory disorders. Suppression of the acute phase response and normalization of SAA levels are likely to significantly impact on the incidence of amyloidosis in inflammatory arthritis.

C-reactive protein and serum amyloid A protein in neonatal infections

In this study, we examine C-reactive protein (CRP) and serum amyloid protein A (SAA). Although the former is the best known and most commonly used indicator of inflammation, certain considerations underline the inadequacy of CRP determination alone for the early diagnosis of infection. In fact symptoms often precede the CRP elevation. SAA protein comprises a family of polymorphic apolipoproteins produced mainly by the liver, and several studies have stressed its importance in the diagnosis and monitoring of various diseases. Pathological SAA values are often detected in association with normal CRP concentrations. SAA rises earlier and more sharply than CRP. Finally, contrary to CRP, SAA presents the same trend in viral as well as bacterial infections. Although the data available on SAA in neonates are currently very limited, it is possible to postulate a role of primary importance for SAA in the management of neonatal infections.

The acute phase protein serum amyloid A (SAA) as an inflammatory marker in equine influenza virus infection

The acute phase protein serum amyloid A (SAA) has proven potentially useful as an inflammatory marker in the horse, but the knowledge of SAA responses in viral diseases is limited. The aim of this study was to evaluate SAA as a marker for acute equine influenza A2 (H3N8) virus infection. This is a highly contagious, serious condition that inflicts suffering on affected horses and predisposes them to secondary bacterial infections and impaired performance. Seventy horses, suffering from equine influenza, as verified by clinical signs and seroconversion, were sampled in the acute (the first 48 h) and convalescent (days 11-22) stages of the disease, and SAA concentrations were determined. Clinical signs and rectal temperature were recorded. Secondary infections, that could have influenced SAA concentrations, were clinically suspected in 4 horses. SAA concentrations were higher in the acute stage than in the convalescent stage, and there was a statistically positive relationship between acute stage SAA concentrations and clinical signs and between acute stage SAA concentrations and maximal rectal temperature. Horses sampled early in the acute stage had lower SAA concentrations than those sampled later, indicating increasing concentrations during the first 48 h. There was a statistically positive relationship between convalescent SAA concentrations and degree of clinical signs during the disease process. The results of this investigation indicate that equine SAA responds to equine influenza infection by increasing in concentration during the first 48 h of clinical signs and returning to baseline within 11-22 days in uncomplicated cases.

Using serum amyloid A to screen dairy cows for sub-clinical inflammation

In this study, 232 lactating dairy cows from six herds were observed for clinical signs of inflammation and simultaneously had blood samples drawn to determine whether or not Serum Amyloid A (SAA) was present. Serum protein electrophoresis and white blood cell differential count revealed inflammation in SAA+ samples but not in SAA-samples. Using positive SAA test results as the standard for presence of inflammation, clinical findings consistent with inflammation concurred with positive SAA results only 26% of the time (p<.001) while the lack of clinical signs consistent with inflammation concurred with negative SAA results 95% of the time (p<.001). There was also a significant difference (p<.005) in management styles in that cows permanently fed on wilted/cured forages and kept inside had a 26% prevalence of positive SAA blood samples whereas the overall prevalence of SAA+ samples was 16%. These findings indicate that whole herd screening using SAA can be of value to the veterinarian in helping to identify cows with inflammatory diseases. From a public health perspective, SAA testing of cows going to market can help differentiate those not needing intensive inspection from those that do.

Serum amyloid A versus C-reactive protein in acute pancreatitis: clinical value of an alternative acute-phase reactant

OBJECTIVES

The acute-phase reactant C-reactive protein (CRP) is currently the serum variable of choice for an early, accurate, and cost-effective severity assessment of acute pancreatitis in the daily clinical routine. Serum amyloid A (SAA) proteins comprise a family of apolipoproteins that constitute another major acute-phase reactant and thus could be a potential alternative to CRP assessment. In the present study we investigated the clinical usefulness of SAA determinations in acute pancreatitis using an automated immunoassay technique.

DESIGN

Cohort study, comparing patients with complicated and mild acute pancreatitis; control groups included individuals with further abdominal disorders and healthy volunteers.

SETTING

A collaborative study between the department of general surgery and the routine laboratory of the department of clinical chemistry/pathobiochemistry.

PATIENTS

We enrolled 66 patients with acute pancreatitis in the present study. Control groups consisted of healthy subjects (n = 30), patients with chronic pancreatitis (n = 20), patients with pancreatic carcinoma (n = 20), and patients with acute appendicitis (n = 20).

INTERVENTIONS

Blood samples were collected during 14 consecutive days in patients with acute pancreatitis. A single blood specimen was taken in all control groups after the diagnosis was established.

MEASUREMENTS AND MAIN RESULTS

SAA concentrations were 3 mg/L (median; range, 3-93) in healthy subjects. Although SAA and CRP both reached their maximum within 4 days after onset of symptoms in patients with acute pancreatitis, SAA concentrations rose faster above normal ranges and reached 676 mg/L (median; range, 12-1880), higher than CRP, which reached 313 mg/L (median; range, 29-613). As observed for CRP, SAA was significantly higher in patients who developed complications such as necrosis, infection of necrosis, or multiple organ dysfunction syndrome or in patients who died. SAA achieved best results in discriminating between necrotizing pancreatitis and interstitial edematous pancreatitis. However, CRP provided an earlier differentiation between both entities and a significantly better overall accuracy, as shown by receiver operating characteristics analysis. SAA concentrations in patients with chronic pancreatitis were 6 mg/L (median; range, 3-756). In patients with pancreatic carcinoma, SAA concentrations were 7 mg/L (median; range, 3-492), and in patients with acute appendicitis, they were 50 mg/L (median; range, 3-2140).

CONCLUSION

SAA is a nonspecific and rapidly produced variable in inflammatory abdominal disorders with a wider dynamic range than CRP. The current assay technique renders SAA an applicable and readily available variable under clinical routine conditions. In cases of acute pancreatitis, however, CRP is still superior to SAA for early and accurate stratification of patients with a complicated course.

The acute-phase protein response to human immunodeficiency virus infection in human subjects

Although several studies have shown that asymptomatic human immunodeficiency virus infection elicits an increase in whole body protein turnover, it is not known whether this increased protein turnover includes changes in the kinetics of acute-phase proteins (APPs). To answer this question, we measured 1) the plasma concentrations of four positive (C-reactive protein, alpha1-antitrypsin, haptoglobin, and fibrinogen) and four negative APPs [albumin, high-density lipoprotein (HDL)-apolipoprotein (apo) A1, transthyretin, and retinol-binding protein] and 2) the fractional (FSR) and absolute (ASRs) synthesis rates of three positive and three negative APPs using a constant intravenous infusion of [2H5]phenylalanine in five subjects with symptom-free acquired immunodeficiency syndrome (AIDS) and five noninfected control subjects. Compared with the values of the controls, the plasma concentrations, FSRs, and ASRs of most positive APPs were higher in the AIDS group. The negative APPs had faster FSRs in the AIDS group, there was no difference between the ASRs of the two groups, and only HDL-apoA1 had a lower plasma concentration. These results suggest that symptom-free AIDS elicits an APP response that is different from bacterial infections, as the higher concentrations and faster rates of synthesis of the positive APPs are not accompanied by lower concentrations and slower rates of synthesis of most of the negative APPs.

A non-competitive chemiluminescence enzyme immunoassay for the equine acute phase protein serum amyloid A (SAA) -- a clinically useful inflammatory marker in the horse

A non-competitive chemiluminescence enzyme immunoassay for measuring serum amyloid A (SAA) in equine serum was developed. A polyclonal anti-equine-amyloid A antiserum specific for equine SAA was utilized, and the assay was standardized using highly purified equine SAA. An acute phase horse serum was calibrated against the purified SAA and was used as standard when running the assay. Serum SAA concentrations in the range of 3-1210 mg/l could be measured. The reference range of SAA in clinically healthy adult horses was <7 mg/l. The clinical validation of the assay comprised the SAA responses after surgery and experimentally induced aseptic arthritis, and those associated with viral and bacterial infections. The SAA response after surgery (castration) was consistent, with peak concentrations on day 2 and a return to normal SAA concentrations within eight days. The aseptic arthritis produced an SAA response with a pattern similar to that seen after surgery, with peak concentrations of SAA 36-48 h after induction. Seven horses showed a biphasic pattern, with a second rise in SAA concentrations on day 4 and 5. All animals had SAA levels <7 mg/l on day 15. All horses with viral and bacterial infections had SAA concentrations above 7 mg/l. The ranges of SAA concentrations following the different types of inflammation overlap, being consistent with the unspecific nature of the SAA response. This study revealed that SAA is a sensitive and unspecific marker for inflammation, and describes the dynamics of the SAA response after standardized and well defined tissue damage.

Serum amyloid A (SAA): a concise review of biology, assay methods and clinical usefulness

Serum amyloid A (SAA) is a family of proteins encoded in a multigene complex. Acute phase isotypes SAA1 and SAA2 are synthesized in response to inflammatory cytokines. SAA and C-reactive protein (CRP) are now the most sensitive indicators for assessing inflammatory activity. In viral infection and kidney allograft rejection, SAA proved more useful than CRP. Development of convenient assay methods for SAA will facilitate its use in clinical laboratories.

The acute phase protein serum amyloid A (SAA) as an inflammatory marker in equine influenza virus infection

The acute phase protein serum amyloid A (SAA) has proven potentially useful as an inflammatory marker in the horse, but the knowledge of SAA responses in viral diseases is limited. The aim of this study was to evaluate SAA as a marker for acute equine influenza A2 (H3N8) virus infection. This is a highly contagious, serious condition that inflicts suffering on affected horses and predisposes them to secondary bacterial infections and impaired performance. Seventy horses, suffering from equine influenza, as verified by clinical signs and seroconversion, were sampled in the acute (the first 48 h) and convalescent (days 11-22) stages of the disease, and SAA concentrations were determined. Clinical signs and rectal temperature were recorded. Secondary infections, that could have influenced SAA concentrations, were clinically suspected in 4 horses. SAA concentrations were higher in the acute stage than in the convalescent stage, and there was a statistically positive relationship between acute stage SAA concentrations and clinical signs and between acute stage SAA concentrations and maximal rectal temperature. Horses sampled early in the acute stage had lower SAA concentrations than those sampled later, indicating increasing concentrations during the first 48 h. There was a statistically positive relationship between convalescent SAA concentrations and degree of clinical signs during the disease process. The results of this investigation indicate that equine SAA responds to equine influenza infection by increasing in concentration during the first 48 h of clinical signs and returning to baseline within 11-22 days in uncomplicated cases.

The first international standard for serum amyloid A protein (SAA). Evaluation in an international collaborative study

An ampouled preparation of acute phase serum rich in serum amyloid A protein (SAA) was evaluated in seven laboratories in six countries for its suitability to serve as the international standard for immunoassay of SAA. A variety of different immunoassays were used. On the basis of the results reported here and with the authorization of the Expert Committee on Biological Standardization of the World Health Organization (WHO) this preparation (coded 92/680) was established as the first international standard of SAA.

Serum amyloid A and high density lipoprotein participate in the acute phase response of Kawasaki disease

In this study we report changes in HDL concentration and composition in acute and convalescent Kawasaki disease. Notable reductions in plasma HDL-cholesterol (0.54 +/- 0.2 mmol/L, normal level 0.7-1.81 mmol/L) and apolipoprotein A-I (apoA-I) (56 +/- 28 mg/dL, normal level 141 +/- 22 mg/dL) were observed in all 24 patients studied during the acute phase of Kawasaki disease. These changes were accompanied by the marked appearance of serum amyloid A (SAA) protein in the plasma, associated with HDL3-like lipoprotein particles. The distribution of apoA-I was analyzed in five patients and showed a significant increase in lipid-free apoA-I in the bottom fraction (28.8 +/- 4.1%, normal range 10-15%), suggesting displacement of apoA-I from the HDL particles by SAA. Within 2 wk after acute Kawasaki disease, levels of HDL-cholesterol and apoA-I returned to the normal range, and SAA disappeared from the plasma. The HDL of patients with Kawasaki disease was markedly enriched in triglyceride even in the absence of changes in total plasma triglyceride. The core composition of HDL returned to the normal range more slowly than the plasma HDL-cholesterol and apoA-I levels. This suggests that Kawasaki disease has a profound effect on the lipoprotein profile acutely and a more subtle sustained effect on the HDL composition. We interpret these changes as manifestations of the acute phase response in Kawasaki disease.

Acute phase proteins in the monitoring of inflammatory disorders

The acute phase reaction is in most circumstances a good indicator of (local) inflammatory activity and tissue damage. CRP is a direct and quantitative measure for the acute phase reaction and due to its fast kinetics provides adequate information of the actual situation. The ESR on the contrary is in fact an indirect measure of the acute phase reaction. It does react much slower to changes of inflammatory activity and is influenced by a number of other factors. From studies on the 'behaviour' of CRP it has become clear that diseases may differ with regard to the extent in which they induce an acute phase response. Incidental measurement of the CRP level may add to the diagnostic procedure in selected cases, e.g. in the differentiation between a bacterial and a viral infection or between a bacterial infection and an exacerbation of diseases like SLE. In case of an extremely elevated CRP level (> 100 mg/litre) the possibility of a bacterial infection should always be considered. In clinical practice CRP is particularly useful when serial measurements are performed. The course of the CRP level may be useful for the monitoring of the effect of treatment and for the early detection of postoperative complications or intercurrent infections. The relationship between CRP and the local production and effects of cytokines on the one hand, and the possible functional role of CRP in the inflammatory process on the other hand have surely added a dimension to the clinical use of CRP as a parameter of inflammatory activity.

Serum amyloid A: an acute phase apolipoprotein and precursor of AA amyloid

Serum amyloid A is an acute phase protein complexed to HDL as an apoprotein. The molecular weight is 11.4-12.5 kDa in different species and the protein has from 104 to 112 amino acids, without or with an insertion of eight amino acids at position 72. The protein is very well conserved throughout evolution, indicating an important biological function. The N-terminal part of the molecule is hydrophobic and probably responsible for the lipid binding properties. The most conserved part is from position 38 to 52 and this part is therefore believed to be responsible for the until now unknown biological function. The protein is coded on chromosome 11p in man, and chromosome 7 in mice, and found in all mammals until now investigated, and also in the Peking duck. In the rat a truncated SAA mRNA has been demonstrated, but no equivalent serum protein has been reported. Acute phase SAA is first of all produced in hepatocytes after induction by cytokines, but extrahepatic expression of both acute phase and constitutive SAA proteins have been demonstrated. Several cytokines, first of all IL-1, IL-6 and TNF are involved in the induction of SAA synthesis, but the mutual importance of these cytokines seems to be cell-type specific and to vary in various experimental settings. The role of corticosteroids in SAA induction is somewhat confusing. In most in vitro studies corticosteroids show an enhancing or synergistic effect with cytokines on SAA production in cultured cell. However, in clinical studies and in vivo studies in animals an inhibitory effect of corticosteroids is evident, probably due to the all over anti-inflammatory effect of the drug. Until now no drug has been found that selectively inhibits SAA production by hepatocytes. Effective anti-inflammatory or antibacterial treatment is the only tool for reducing SAA concentration in serum and reducing the risk of developing secondary amyloidosis. The function of SAA is still unclear. Interesting theories, based on current knowledge of the lipid binding properties of the protein and the relation to macrophages, in the transportation of cholesterol from damaged tissues has been advanced. A putative role in cholesterol metabolism is supported by the findings of SAA as an inhibitor of LCAT. The potential that SAA is a modifying protein in inflammation influencing the function of neutrophils and platelets is interesting and more directly related to the inflammatory process itself.(ABSTRACT TRUNCATED AT 400 WORDS)