Complement Activation by C-Reactive Protein Is Critical for Protection of Mice Against Pneumococcal Infection

C-reactive protein lowers the serum level of IL-17, but not TNF-α, and decreases the incidence of collagen-induced arthritis in mice

The biosynthesis of C-reactive protein (CRP) in the liver is increased in inflammatory diseases including rheumatoid arthritis. Previously published data suggest a protective function of CRP in arthritis; however, the mechanism of action of CRP remains undefined. The aim of this study was to evaluate the effects of human CRP on the development of collagen-induced arthritis (CIA) in mice which is an animal model of autoimmune inflammatory arthritis. Two CRP species were employed: wild-type CRP which binds to aggregated IgG at acidic pH and a CRP mutant which binds to aggregated IgG at physiological pH. Ten CRP injections were given on alternate days during the development of CIA. Both wild-type and mutant CRP reduced the incidence of CIA, that is, reduced the number of mice developing CIA; however, CRP did not affect the severity of the disease in arthritic mice. The serum levels of IL-17, IL-6, TNF-α, IL-10, IL-2 and IL-1β were measured: both wild-type and mutant CRP decreased the level of IL-17 and IL-6 but not of TNF-α, IL-10, IL-2 and IL-1β. These data suggest that CRP recognizes and binds to immune complexes, although it was not clear whether CRP functioned in its native pentameric or in its structurally altered pentameric form in the CIA model. Consequently, ligand-complexed CRP, through an as-yet undefined mechanism, directly or indirectly, inhibits the production of IL-17 and eventually protects against the initiation of the development of arthritis. The data also suggest that IL-17, not TNF-α, is critical for the development of autoimmune inflammatory arthritis.

The dichotomic role of single cytokines: Fine-tuning immune responses

Cytokines are known for their pleiotropic effects. They can be classified by their function as pro-inflammatory, such as tumor necrosis factor (TNF), interleukin (IL) 1 and IL-12, or anti-inflammatory, like IL-10, IL-35 and transforming growth factor β (TGF-β). Though this type of classification is an important simplification for the understanding of the general cytokine's role, it can be misleading. Here, we discuss recent studies that show a dichotomic role of the so-called pro and anti-inflammatory cytokines, highlighting that their function can be dependent on the microenvironment and their concentrations. Furthermore, we discuss how the back-and-forth interplay between cytokines and immunometabolism can influence the dichotomic role of inflammatory responses as an important target to complement cytokine-based therapies.

C-Reactive Protein Levels Are Associated with Complement C4 Deposits and Interstitial Arteritis in ANCA-Associated Renal Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a potentially life-threatening systemic small-vessel vasculitis that is characterized by pauci-immune glomerulonephritis in case of kidney involvement, representing a major denominator of AAV mortality. Innate immunity with complement system activation is increasingly recognized in the pathogenesis of AAV and as an attractive therapeutic target. Although C-reactive protein (CRP) was thought to be a passive, nonspecific marker of inflammation, recent studies indicate that CRP plays a key role in the innate immune system by recognizing pathogens and altered self-determinants. Elevated baseline CRP at disease onset of AAV has already been described as a determinant of poor long-term outcomes. However, its clinical implications at disease onset of AAV, with respect to vasculitis manifestations and complement system activation that might also affect long-term outcomes, remain elusive. CRP levels were retrospectively analyzed in 53 kidney-biopsy-confirmed cases of ANCA-associated renal vasculitis; a total of 138 disease controls were also evaluated. Univariate and multivariate regression analysis was performed on clinicopathological parameters associated with CRP levels in ANCA-associated renal vasculitis. Results: Compared to disease controls, CRP elevation was common in ANCA-associated renal vasculitis and associated with de novo disease (p = 0.0169), critical illness (p = 0.0346), and severe deterioration of kidney function (p = 0.0167), independent of extrarenal disease manifestations. As confirmed by multiple regression analysis, CRP levels were correlated with active lesions predominated by interstitial arteritis in renal vasculitis, specifically with MPO-ANCA seropositivity (p = 0.0017). Based on analysis of systemic complement system activation and intrarenal complement deposits, CRP elevation was correlated specifically with complement C4 deposits in interstitial arteries in the subgroup with myeloperoxidase (MPO)-ANCA seropositivity (p = 0.039). Finally, this association was independent of systemic complement system activation, as reflected by the consumption of respective complement components. Here, we expand our current understanding of CRP in ANCA-associated renal vasculitis not only as an inflammatory marker, but potentially also as being involved in the pathogenesis of kidney injury by interaction with the complement system.

Albumin Infusion May Improve the Prognosis of Critical COVID-19 Patients with Hypoalbuminemia in the Intensive Care Unit: A Retrospective Cohort Study

Background

The coronavirus disease 2019 (COVID-19) pandemic has caused enormous mortality worldwide. Low albumin level is a risk factor for increasing mortality among patients in the intensive care unit (ICU). This study investigated the effect of albumin infusion on critical COVID-19 patients with hypoalbuminemia.

Methods

A total of 114 COVID-19 ICU patients with hypoalbuminemia were recruited from Wuhan Leishenshan Hospital and Zhongnan Hospital of Wuhan University. Clinical features and laboratory variables were collected through electronic medical records. The cohorts were divided into two groups: albumin infusion and non-albumin infusion. Propensity-matched analysis was used to compare patients who received albumin to controls. Statistical analyses were used to investigate the survival time and inflammation-related blood biomarkers between groups.

Results

Lactate dehydrogenase, interleukin (IL)-6, IL-2 receptor, and IL-8 levels were significantly downregulated in the albumin infusion group. Significant upregulations of lymphocyte counts and IL-10 were found in the albumin infusion group. There was a negative association between albumin level and D-dimer or procalcitonin levels after treatment. The albumin infusion group had a significantly longer survival time and shorter hospitalization time than control patients. Notably, a 1g increase in albumin level reduced the risk of death by approximately 7.3% after adjusting for age and sex. Patients with increased albumin levels after treatment had better prognoses than those without.

Conclusion

Albumin administration can regulate COVID-19-related biomarkers and reduce the risk of death in critical patients with hypoalbuminemia. Clinicians should pay more attention to these risk factors. Targeted clinical interventions should be implemented to minimize the negative impacts of hypoalbuminemia and improve disease outcomes.

Structurally Altered, Not Wild-Type, Pentameric C-Reactive Protein Inhibits Formation of Amyloid-β Fibrils

The structure of wild-type pentameric C-reactive protein (CRP) is stabilized by two calcium ions that are required for the binding of CRP to its ligand phosphocholine. CRP in its structurally altered pentameric conformations also binds to proteins that are denatured and aggregated by immobilization on microtiter plates; however, the identity of the ligand on immobilized proteins remains unknown. We tested the hypotheses that immobilization of proteins generated an amyloid-like structure and that amyloid-like structure was the ligand for structurally altered pentameric CRP. We found that the Abs to amyloid-β peptide 1-42 (Aβ) reacted with immobilized proteins, indicating that some immobilized proteins express an Aβ epitope. Accordingly, four different CRP mutants capable of binding to immobilized proteins were constructed, and their binding to fluid-phase Aβ was determined. All CRP mutants bound to fluid-phase Aβ, suggesting that Aβ is a ligand for structurally altered pentameric CRP. In addition, the interaction between CRP mutants and Aβ prevented the formation of Aβ fibrils. The growth of Aβ fibrils was also halted when CRP mutants were added to growing fibrils. Biochemical analyses of CRP mutants revealed altered topology of the Ca2+-binding site, suggesting a role of this region of CRP in binding to Aβ. Combined with previous reports that structurally altered pentameric CRP is generated in vivo, we conclude that CRP is a dual pattern recognition molecule and an antiamyloidogenic protein. These findings have implications for Alzheimer's and other neurodegenerative diseases caused by amyloidosis and for the diseases caused by the deposition of otherwise fluid-phase proteins.

Relevance of lipoproteins, membranes, and extracellular vesicles in understanding C-reactive protein biochemical structure and biological activities

Early purification protocols for C-reactive protein (CRP) often involved co-isolation of lipoproteins, primarily very low-density lipoproteins (VLDLs). The interaction with lipid particles was initially attributed to CRP’s calcium-dependent binding affinity for its primary ligand—phosphocholine—the predominant hydrophilic head group expressed on phospholipids of most lipoprotein particles. Later, CRP was shown to additionally express binding affinity for apolipoprotein B (apo B), a predominant apolipoprotein of both VLDL and LDL particles. Apo B interaction with CRP was shown to be mediated by a cationic peptide sequence in apo B. Optimal apo B binding required CRP to be surface immobilized or aggregated, treatments now known to structurally change CRP from its serum soluble pentamer isoform (i.e., pCRP) into its poorly soluble, modified, monomeric isoform (i.e., mCRP). Other cationic ligands have been described for CRP which affect complement activation, histone bioactivities, and interactions with membranes. mCRP, but not pCRP, binds cholesterol and activates signaling pathways that activate pro-inflammatory bioactivities long associated with CRP as a biomarker. Hence, a key step to express CRP’s biofunctions is its conversion into its mCRP isoform. Conversion occurs when (1) pCRP binds to a membrane surface expressed ligand (often phosphocholine); (2) biochemical forces associated with binding cause relaxation/partial dissociation of secondary and tertiary structures into a swollen membrane bound intermediate (described as mCRP_m or pCRP*); (3) further structural relaxation which leads to total, irreversible dissociation of the pentamer into mCRP and expression of a cholesterol/multi-ligand binding sequence that extends into the subunit core; (4) reduction of the CRP subunit intrachain disulfide bond which enhances CRP’s binding accessibility for various ligands and activates acute phase proinflammatory responses. Taken together, the biofunctions of CRP involve both lipid and protein interactions and a conformational rearrangement of higher order structure that affects its role as a mediator of inflammatory responses.

Biomarkers of sepsis in pigs, horses and cattle: from acute phase proteins to procalcitonin

Sepsis is a complex clinical syndrome triggered by an inflammatory host response to an infection. It is usually complicated to detect and diagnose, and has severe consequences in human and veterinary health, especially when treatment is not started early. Therefore, efforts to detect sepsis accurately are needed. In addition, its proper diagnosis could reduce the misuse of antibiotics, which is essential fighting against antimicrobial resistance. This case is a particular issue in farm animals, as antibiotics have been traditionally given massively, but now they are becoming increasingly restricted. When sepsis is suspected in animals, the most frequently used biomarkers are acute phase proteins such as C-reactive protein, serum amyloid A and haptoglobin, but their concentrations can increase in other inflammatory conditions. In human patients, the most promising biomarkers to detect sepsis are currently procalcitonin and presepsin, and there is a wide range of other biomarkers under study. However, there is little information on the application of these biomarkers in veterinary species. This review aims to describe the general concepts of sepsis and the current knowledge about the biomarkers of sepsis in pigs, horses, and cattle and to discuss possible advances in the field.

Clinical features and Outcomes of Cryptococcemia patients with and without HIV infection

BACKGROUND

The effects of cryptococcemia on patient outcomes in those with or without HIV remain unclear.

METHODS

One hundred and seventy-nine cryptococcemia patients were enrolled in this retrospective study. Demographic characteristics, blood test results and outcome were compared between the two groups.

RESULTS

The diagnosis time of Cryptococcus infection was 2.0(0-6.0) days for HIV-infected patients, 5.0 (1.5-8.0) days for HIV-uninfected patients (p = .008), 2.0 (1.0-6.0) days for cryptococcal meningitis (CM) patients and 6.0 (5.0-8.0) days for non-CM patients (p < .001). HIV infection [adjusted odds ratio (AOR) (95% confidence interval): 6.0(2.3-15.9)], CRP < 15 mg/L [AOR:3.7(1.7-8.1)) and haemoglobin > 110 g/L [AOR:2.5(1.2-5.4)] were risk factors for CM development. Forty-six (25.7%) patients died within 90 days. ICU stay [AOR:2.8(1.1-7.1)], hypoalbuminemia [AOR:2.7(1.4-5.3)], no anti-cryptococcal treatment [AOR:4.7(1.9-11.7)] and altered consciousness [AOR:2.4(1.0-5.5)] were independent risk factors for 90-day mortality in all patients. HIV infection did not increase the 90-day mortality of cryptococcemia patients when anti-Cryptococcus treatment was available. Non-Amphotericin B treatment [AOR:3.4(1.0-11.2)] was associated with 90-day mortality in HIV-infected patients, but age ≥ 50.0 years old [AOR:2.7(1.0-2.9)], predisposing disease [AOR:4.1(1.2-14.2)] and altered consciousness [AOR:3.7(1.1-12.9)] were associated with 90-day mortality in HIV-uninfected patients who accepted anti-Cryptococcus treatment.

CONCLUSION

HIV infection increased the incidence of CM rather than mortality in cryptococcemia patients. The predictive model was completely divergent in HIV-infected and HIV-uninfected patients, suggesting that novel strategies for diagnosis and treatment algorithms are urgently needed.

C-Reactive Protein-Based Strategy to Reduce Antibiotic Dosing for the Treatment of Pneumococcal Infection

C-reactive protein (CRP) is a component of innate immunity. The concentration of CRP in serum increases in microbial infections including Streptococcus pneumoniae infection. Employing a mouse model of pneumococcal infection, it has been shown that passively administered human wild-type CRP protects mice against infection, provided that CRP is injected into mice within two hours of administering pneumococci. Engineered CRP (E-CRP) molecules have been reported recently; unlike wild-type CRP, passively administered E-CRP protected mice against infection even when E-CRP was injected into mice after twelve hours of administering pneumococci. The current study was aimed at comparing the protective capacity of E-CRP with that of an antibiotic clarithromycin. We established a mouse model of pneumococcal infection in which both E-CRP and clarithromycin, when used alone, provided minimal but equal protection against infection. In this model, the combination of E-CRP and clarithromycin drastically reduced bacteremia and increased survival of mice when compared to the protective effects of either E-CRP or clarithromycin alone. E-CRP was more effective in reducing bacteremia in mice treated with clarithromycin than in untreated mice. Also, there was 90% reduction in antibiotic dosing by including E-CRP in the antibiotic-treatment for maximal protection of infected mice. These findings provide an example of cooperation between the innate immune system and molecules that prevent multiplication of bacteria, and that should be exploited to develop novel combination therapies for infections against multidrug-resistant pneumococci. The reduction in antibiotic dosing by including E-CRP in the combination therapy might also resolve the problem of developing antibiotic resistance.

Treatment of Pneumococcal Infection by Using Engineered Human C-Reactive Protein in a Mouse Model

C-reactive protein (CRP) binds to several species of bacterial pathogens including Streptococcus pneumoniae. Experiments in mice have revealed that one of the functions of CRP is to protect against pneumococcal infection by binding to pneumococci and activating the complement system. For protection, however, CRP must be injected into mice within a few hours of administering pneumococci, that is, CRP is protective against early-stage infection but not against late-stage infection. It is assumed that CRP cannot protect if pneumococci got time to recruit complement inhibitor factor H on their surface to become complement attack-resistant. Since the conformation of CRP is altered under inflammatory conditions and altered CRP binds to immobilized factor H also, we hypothesized that in order to protect against late-stage infection, CRP needed to change its structure and that was not happening in mice. Accordingly, we engineered CRP molecules (E-CRP) which bind to factor H on pneumococci but do not bind to factor H on any host cell in the blood. We found that E-CRP, in cooperation with wild-type CRP, was protective regardless of the timing of administering E-CRP into mice. We conclude that CRP acts via two different conformations to execute its anti-pneumococcal function and a model for the mechanism of action of CRP is proposed. These results suggest that pre-modified CRP, such as E-CRP, is therapeutically beneficial to decrease bacteremia in pneumococcal infection. Our findings may also have implications for infections with antibiotic-resistant pneumococcal strains and for infections with other bacterial species that use host proteins to evade complement-mediated killing.