Complement and IL-12: yin and yang

Post-acute sequelae of SARS-CoV-2 cardiovascular symptoms are associated with trace-level cytokines that affect cardiomyocyte function

An estimated 65 million people globally suffer from post-acute sequelae of COVID-19 (PASC), with many experiencing cardiovascular symptoms (PASC-CVS) like chest pain and heart palpitations. This study examines the role of chronic inflammation in PASC-CVS, particularly in individuals with symptoms persisting over a year after infection. Blood samples from three groups-recovered individuals, those with prolonged PASC-CVS and SARS-CoV-2-negative individuals-revealed that those with PASC-CVS had a blood signature linked to inflammation. Trace-level pro-inflammatory cytokines were detected in the plasma from donors with PASC-CVS 18 months post infection using nanotechnology. Importantly, these trace-level cytokines affected the function of primary human cardiomyocytes. Plasma proteomics also demonstrated higher levels of complement and coagulation proteins in the plasma from patients with PASC-CVS. This study highlights chronic inflammation's role in the symptoms of PASC-CVS.

Tumour cell conditioned medium reveals greater M2 skewing of macrophages in the absence of properdin

Introduction

The tumour microenvironment is shaped by the interaction of immune, non immune, and tumour cells present in close proximity. Tumour cells direct the development of a locally immune suppressed state, affecting the activity of anti tumour T cells and preparing the escape phase of tumour development. Macrophages in the tumour typically develop into so‐called tumour associated macrophages with a distinct profile of activities which lead to a reduction in inflammation and antigen presentation. The direct impact of tumour cell conditioned medium on the activity profile of macrophages in dependence of their complement component expression has not yet been investigated.

Methods

In our in vitro study, macrophages differentiated from bone marrows of properdin deficient and wildtype mice were stimulated with conditioned medium of a syngeneic tumour cell line, B16F10, a mouse melanoma subline.

Results

In comparison with macrophages from wildtype mice, those from congenic properdin deficient mice showed skewing towards M2 profile, encompassing mRNA expression for genes involved in arginine metabolism, production of type 2 cytokines, and relatively lower surface expression of molecules needed for antigen presentation.

Conclusions

These data suggest that properdin insufficiency promotes a tumour environment that helps the tumour evade the immune response.

Major histocompatibility complex class III (C2, C4, factor B) and C3 gene variants in patients with pulmonary tuberculosis

The complement system is an integral part of the host immune system and plays an immunoregulatory role at the interface of innate and acquired immune responses. Limited data are available on the influence of variations in complement genes in infectious diseases such as pulmonary tuberculosis (PTB). The aim of this study was to investigate the role of genetic variations in complement system components C2, C4, BF, and C3 in PTB (n = 125) compared with healthy controls (n = 125) in the Indian population. The study showed, for the first time, an increased occurrence of null alleles at the C4A, i.e., C4AQ0; an increased frequency of BF*FA and C3*F in patients with PTB compared with healthy individuals, and contributed a risk with odds ratios of 18.16 (95% confidence interval [CI] = 3.0-108.6, p = 0.0004), 2.9 (95% CI = 1.9-4.37, p(c) = 3.15E-06), and 2.26 (95% CI = 1.5-3.3, p(c) = 6.7E-05), respectively. A combinatorial analysis of complement gene variants as risk determinants and their phenotypic effects in various populations may provide unique insights into the genetic basis of susceptibility to PTB.

Lipoxins as an immune-escape mechanism

Here, we discuss the mechanisms of repression of signaling pathways that are triggered by Lipoxin (LX) and are responsible for control of pro-inflammatory response during chronic phase of Toxoplasma gondii infection. We also discuss this mechanism from the perspective of the pathogen, which pirates the host's lipoxygenase machinery to its own advantage as a probable immune-escape mechanism. Pro-inflammatory mediators such as IL-12, IFN-gamma and TNF are essential in controlling parasite growth during T. gondii infection. However, it is clear that exacerbated production of these cytokines results in host tissue damage. LX, an anti-inflammatory eicosanoid, plays an important role in regulation of immune response to T. gondii.

A role for tumour necrosis factor-alpha, complement C5 and interleukin-6 in the initiation and development of the mycobacterial cord factor trehalose 6,6'-dimycolate induced granulomatous response

Trehalose 6,6'-dimycolate (TDM) is a glycolipid component of the mycobacterial cell wall that causes immune responses in mice similar to Mycobacterium tuberculosis (MTB) infection, including granuloma formation with production of proinflammatory cytokines. The precise roles of tumour necrosis factor (TNF)-alpha, complement C5 and interleukin (IL)-6 in the molecular events that lead to the initiation and maintenance of the granulomatous response to TDM have not been fully elucidated. Macrophage proinflammatory responses from wild-type and complement-deficient mice after infection with MTB were assessed, and compared to responses from organisms in which surface TDM had been removed. Removal of TDM abolished proinflammatory responses, markedly so in the complement-deficient macrophages. Mice deficient in TNF-alpha, C5a and IL-6, along with wild-type C57BL/6 controls, were intravenously injected with TDM in a water-in-oil emulsion, and analysed for histological response and cytokine production in lungs. Wild-type C57BL/6 mice formed granulomas with increased production of IL-1beta, IL-6, TNF-alpha, macrophage inflammatory protein-1alpha (MIP-1alpha), IL-12p40, interferon-gamma (IFN-gamma), and IL-10 protein and mRNA. TNF-alpha-deficient mice failed to produce a histological response to TDM, with no increases in cytokine production following TDM administration. While C5a-deficient mice exhibited inflammation, they did not form structured granulomas and initially had decreased production of proinflammatory mediators. IL-6-deficient mice initiated granuloma formation, but failed to maintain the granulomas through day 7 and demonstrated decreased early production of proinflammatory mediators in comparison to wild-type mice. These data suggest that TNF-alpha is critical for initiation of the granulomatous response, C5a is necessary for formation of cohesive granulomas, and IL-6 plays a key role in the granuloma maintenance response to mycobacterial TDM.

Porcine IL12A and IL12B gene mapping, variation and evidence of association with lytic complement and blood leucocyte proliferation traits

Interleukin-12, a heterodimeric cytokine consisting of glycosylated subunits of 35 and 40 kDa, is a central molecule in controlling innate as well as adaptive immunity. This study was aimed to investigate the role of IL12A and IL12B as candidate genes for immune competence in pigs. The porcine genes were screened for polymorphism and association analysis was carried out by mixed model analysis with parameters of innate immunity, in vitro haemolytic complement activity in the classical and alternative pathways, in vivo complement activation expressed as C3c serum concentration, and blood leucocyte proliferation measured in F2 animals of a pig resource population based on cross of Duroc and Berlin miniature pig (DUMI resource population). A single nucleotide polymorphism (SNP) in the promoter region (C > A) of IL12A was identified. Two SNPs were detected in intron 4 of IL12B at positions 192 (A > G) and 437 (C > T). Significant effects of IL12 genotypes on complement activity traits and mitogen-induced leucocyte proliferation were found. The IL12A and IL12B genes were assigned to chromosome13 and 16, respectively, by using radiation hybrid analysis and genetic mapping in the DUMI resource population. Mapping and association analyses promote the IL12 genes as functional and positional candidate gene for disease resistance in pigs.

Anaphylatoxins: their role in bacterial infection and inflammation

Activation of the complement system plays a crucial role in the pathogenesis of infection and inflammation. Especially the complement activation products C3a and C5a, known as the anaphylatoxins, are potent proinflammatory mediators. In addition to their evident role in innate immunity, it is clear that the anaphylatoxins also play a role in regulation of adaptive immune responses. The anaphylatoxins play a role in a variety of infectious and inflammatory diseases like sepsis, ischemia-reperfusion injury, immune complex diseases, and hypersensitivity diseases like asthma. In this review we discuss the role of anaphylatoxins in infection and inflammation. Furthermore, we focus on bacterial complement evasion strategies that can provide tools for further research on pathogenesis of infectious diseases and a better understanding of the role of complement and anaphylatoxins in infection and inflammation.

Opposing regulatory roles of complement factor 5 in the development of bleomycin-induced pulmonary fibrosis

The mechanisms of idiopathic pulmonary fibrosis pathogenesis, a chronic and progressive interstitial lung disease, remain elusive. The complement system, a crucial arm of the innate immune response, plays a pivotal role in several pathological disorders; however, the contribution of individual complement components to lung fibrosis has not yet been examined. Complement factor 5 (C5) and its cleavage product C5a are critical mediators in inflammatory diseases. Thus, to evaluate the role of C5 in lung fibrosis, we compared congenic C5-sufficient and C5-deficient mice in a well-characterized murine model of bleomycin-induced pulmonary fibrosis. C5-deficient mice had an exaggerated inflammatory phenotype compared with C5-sufficient mice during acute bleomycin-induced lung injury. These findings suggest a protective and anti-inflammatory role for C5, which was linked to the regulation of matrix metalloproteinases involved in cell migration. In contrast, C5 had a detrimental effect during chronic stages of bleomycin-induced injury, indicating a profibrotic role for C5. This deleterious activity for C5 was associated with expression of the fibrogenic cytokine TGF-beta1 and matrix metalloproteinase-3, an important mediator in fibroblast contraction. Altogether, our data reveal novel and opposing roles for C5 in both inflammation and tissue repair. Furthermore, these findings provide insight into the development of new therapeutic strategies for idiopathic pulmonary fibrosis patients.

Requisite role for complement C5 and the C5a receptor in granulomatous response to mycobacterial glycolipid trehalose 6,6'-dimycolate

The development of pulmonary granulomatous lesions during mycobacterial infection is a complex phenomenon, in part caused by responses elicited towards the surface glycolipid trehalose 6,6'-dimycolate (TDM; cord factor). The molecular mechanisms underlying granuloma formation following challenge with TDM are not yet completely understood. The present study defines pathologic differences in acute response to Mycobacterium tuberculosis TDM in C57BL/6 mice and mice lacking the C5a receptor (C5aR-/-). Mice were intravenously injected with TDM prepared in water-in-oil-in-water emulsion and examined for histologic response and changes in proinflammatory cytokines and chemokines in lung tissue. Control C5a receptor-sufficient mice demonstrated a granulomatous response that peaked between days 4 and 7. Increased production of macrophage inflammatory protein-1 alpha (MIP-1alpha), interleukin-1beta (IL-1beta) and CXC chemokine KC (CXCL1) correlated with development of granulomas, along with modest change in tumor necrosis factor-alpha (TNF-alpha). In contrast, the C5aR-/- mice revealed markedly exacerbated inflammatory response. The receptor-deficient mice also demonstrated a lack of coherent granulomatous response, with severe oedema present and instances of lymphocytic cuffing around pulmonary vessels. Lung weight index was increased in the C5aR-/- mice, correlating with increased MIP-1alpha, KC, IL-1beta and TNF-alpha over that identified in the congenic C5aR-sufficient controls. Correlate experiments performed in C5-deficient (B10.D2-H2d H2-T18c Hco/oSnJ) mice revealed similar results, leading to the conclusion that C5 plays a significant role in mediation of chemotactic and activation events that are the basis for maturation of granulomatous responses to TDM.

An RNA external guide sequence ribozyme targeting human interleukin-4 receptor alpha mRNA

RNA oligonucleotides termed External Guide Sequence (EGS) and RNAi have been described that target specific gene expression by site-specific cleavage of mRNA. EGS serve as an RNA catalyst or ribozyme by directing bound mRNA to the ubiquitous cellular enzyme RNAse P. We describe an EGS targeting human interleukin (IL)-4 receptor alpha mRNA, an important cytokine receptor in the pathogenesis of asthma and allergic disease expressed in pulmonary tissues. This EGS was designed to explore pulmonary delivery of catalytic RNA oligonucleotides as a novel therapy in asthma and other atopic diseases. Inhaled DNA oligonucleotides termed Respirable Antisense OligoNucleotide Sequences (RASONS) are selectively internalized in lung tissues in a complex with endogenous lipid surfactants present in normal lung and can alter pulmonary gene expression. Potential applications of inhaled RNA oligonucleotides in therapy of pulmonary and related systemic diseases are discussed.

Flow cytometric measurement of phagocytosis reveals a role for C3b in metal particle uptake by phagocytes

A methodology for the quick and efficient study of phagocytosis has been developed. It uses the flow cytometer to exploit the change in size and granularity that occurs in cells upon the ingestion of particulate material. The numbers of cells that have phagocytosed particles can be calculated from the distinct shift in regions that occurs. The method also allows the factors governing phagocytosis to be studied in detail through the use of blocking agents or antibodies. Blood-derived monocytes were studied to investigate the role of complement in metal particle phagocytosis to further understand aseptic loosening. Factor C3b was found to be fundamental to the opsonization and phagocytosis of metal particles by monocytes.

Host persistence: exploitation of anti-inflammatory pathways by Toxoplasma gondii

Hosts that are infected with Toxoplasma gondii must mount a powerful immune response to contain dissemination of the parasite and to prevent mortality. After parasite proliferation has been contained by interferon-gamma-dependent responses, the onset of the chronic phase of infection is characterized by continuous cell-mediated immunity. Such potent responses are kept under tight control by a class of anti-inflammatory eicosanoid, the lipoxins. Here, we review such immune-containment strategies from the perspective of the host, which attempts to keep pro-inflammatory responses under control during chronic disease, as well as from the perspective of the pathogen, which hijacks the lipoxygenase machinery of the host for its own advantage, probably as an immune-escape mechanism.

Characterization of C3a and C5a receptors in rat cerebellar granule neurons during maturation. Neuroprotective effect of C5a against apoptotic cell death

There is now clear evidence that the Complement anaphylatoxin C3a and C5a receptors (C3aR and C5aR) are expressed in glial cells, notably in astrocytes and microglia. In contrast, very few data are available concerning the possible expression of these receptors in neurons. Here, we show that transient expression of C3aR and C5aR occurs in cerebellar granule neurons in vivo with a maximal density in 12-day-old rat, suggesting a role of these receptors during development of the cerebellum. Expression of C3aR and C5aR mRNAs and proteins was also observed in vitro in cultured cerebellar granule cells. Quantification of the mRNAs by real-time reverse transcription-PCR showed a peak of expression at day 2 in vitro (DIV 2); the C3aR and C5aR proteins were detected by Western blot analysis at DIV 4 and by flow cytometry and immunocytochemistry in differentiating neurons with a maximum density at DIV 4-9. Apoptosis of granule cells plays a crucial role for the harmonious development of the cerebellar cortex. We found that, in cultured granule neurons in which apoptosis was induced by serum deprivation and low potassium concentration, a C5aR agonist promoted cell survival and inhibited caspase-3 activation and DNA fragmentation. The neuroprotective effect of the C5aR agonist was associated with a marked inhibition of caspase-9 activity and partial restoration of mitochondrial integrity. Our results provide the first evidence that C3aR and C5aR are both expressed in cerebellar granule cells during development and that C5a, but not C3a, is a potent inhibitor of apoptotic cell death in cultured granule neurons.

Asthma, body mass index, and C-reactive protein among US adults

Obesity, a state that may be characterized by a low-grade inflammation, has been associated with asthma. C-reactive protein, an acute phase reactant, is elevated in obese people. However, little is known about how asthma affects C-reactive protein concentrations. Using data from 14,224 participants of the Third National Health and Nutrition Examination Survey (1988-1994), the author examined C-reactive protein concentrations among participants with current asthma (n = 651), who formerly had asthma (n = 303), and who never had asthma (n = 13,270). Compared with 21% of participants with current asthma, 11% with former asthma (P < .001) and 15% without asthma (P = .018) had C-reactive protein concentrations > or = 85th percentile of the sex-specific distribution. Compared with participants without asthma, the age-adjusted odds ratios for having an elevated C-reactive protein concentration was 1.49 (95% confidence interval [CI]: 1.11, 2.00) for persons with current asthma. After adjusting for age, sex, race or ethnicity, years of education, cotinine concentration, body mass index, waist-hip ratio, physical activity level, aspirin use, oral corticosteroid use, and inhaled corticosteroid use, the odds ratio decreased to 1.15 (95% CI: 0.83, 1.59). Body mass index was the main reason for the attenuation of the odds ratio. Whether the inflammatory activity associated with body mass index contributes to the pathophysiology of asthma is unknown.

Mucosal immunotherapy with CpG oligodeoxynucleotides reverses a murine model of chronic asthma induced by repeated antigen exposure

Murine models of acute atopic asthma may be inadequate to study the effects of recurrent exposure to inhaled allergens, such as the epithelial changes seen in asthmatic patients. We developed a murine model in which chronic airway inflammation is maintained by repeated allergen [ovalbumin (OVA)] inhalation; using this model, we examined the response to mucosal administration of CpG DNA (oligonucleotides) and specific antigen immunotherapy. Mice repeatedly exposed to OVA developed significantly greater airway hyperresponsiveness and goblet cell hyperplasia, but not airway eosinophilia, compared with those exposed only twice. CpG-based immunotherapy significantly reversed both acute and chronic markers of inflammation as well as airway hyperresponsiveness. We further examined the effect of mucosal immunotherapy on the response to a second, unrelated antigen. Mice sensitized to both OVA and schistosome eggs, challenged with inhaled OVA, and then treated with OVA-directed immunotherapy demonstrated significant reduction of airway hyperresponsiveness and a moderate reduction in eosinophilia, after inhalation challenge with schistosome egg antigens. In this model, immunotherapy treatment reduced bronchoalveolar lavage (BAL) levels of Th2 cytokines (IL-4, IL-5, IL-13, and IL-10) without changing BAL IFN-gamma. Antigen recall responses of splenocytes from these mice demonstrated an antigen-specific (OVA) enhanced release of IL-10 from splenocytes of treated mice. These results suggest that CpG DNA may provide the basis for a novel form of immunotherapy of allergic asthma. Both antigen-specific and, to a lesser extent, antigen-nonspecific responses to mucosal administration of CpG DNA are seen.

Genetic polymorphisms in IL-10 and IL-12b allele promoter regions in Chinese patients of Han nationality with HBV infection

AIM

To investigate the association of genetic susceptibility to hepatitis B virus infection and disease progression with the allelic polymorphisms of IL-10 and IL-12b promoter regions in Chinese Han population.

METHODS

Two groups of indigenous Chinese subjects (314 subjects in total) were recruited in this study. Group 1 included 104 unrelated patients with chronic hepatitis B virus infection and 76 unrelated healthy donors. Group 2 contained 134 related subjects from seven HBV-infected pedigrees of Han ethnic origin. Total genomic DNA samples were purified from the 1.5 ml of peripheral blood of all participated individuals by using the QIAgen purification DNA kit. Genotyping of IL10-5'A and IL12-5'C alleles was performed by means of PCR-RFLP (restriction fragment length polymorphism) and further proved by direct DNA sequencing. All data were statistically analyzed by using SAS software.

RESULTS

IL10-5'A mutant frequency in unrelated healthy subjects was 41.9% compared with 42.1% in unrelated HBV-infected patients, while IL12-5'C mutant frequency was 64.6% and 55.8% among healthy individuals and HBV-infected patients, respectively. No significant difference was found among the unrelated healthy individuals and unrelated HBV-infected patients. In related individuals from the seven HBV-infected pedigrees, the mutant frequency of IL12-5'C allele was found to be identical to that in unrelated healthy and HBV-infected patients, but the mutant frequency of IL10-5'A allele(19.5%) was significantly different from that(42.0%) in unrelated group (P<0.01).

CONCLUSION

The polymorphisms of IL10-5'A and IL12-5'C allele promoter regions were not correlated with hepatitis B virus infection and disease progression among unrelated subjects, but there was a significantly lower mutant frequency of IL10-5'A allele among related subjects.