Complement C3 F and BF S allotypes are risk factors for Chagas disease cardiomyopathy

Methodological Appraisal of Literature Concerning the Analysis of Genetic Variants or Protein Levels of Complement Components on Susceptibility to Infection by Trypanosomatids: A Systematic Review

Background

Trypanosomatids are protozoa responsible for a wide range of diseases, with emphasis on Chagas Disease (CD) and Leishmaniasis, which are in the list of most relevant Neglected Tropical Diseases (NTD) according to World Health Organization (WHO). During the infectious process, immune system is immediately activated, and parasites can invade nucleated cells through a broad diversity of receptors. The complement system − through classical, alternative and lectin pathways − plays a role in the first line of defense against these pathogens, acting in opsonization, phagocytosis and lysis of parasites. Genetic modifications in complement genes, such as Single Nucleotide Polymorphisms (SNPs), can influence host susceptibility to these parasites and modulate protein expression.

Methods

In March and April 2021, a literature search was conducted at the PubMed and Google Scholar databases and the reference lists obtained were verified. After applying the inclusion and exclusion criteria, the selected studies were evaluated and scored according to eleven established criteria regarding their thematic approach and design, aiming at the good quality of publications.

Results

Twelve papers were included in this systematic review: seven investigating CD and five focusing on Leishmaniasis. Most articles presented gene and protein approaches, careful determination of experimental groups, and adequate choice of experimental techniques, although several of them were not up-to-date. Ten studies explored the association of polymorphisms and haplotypes with disease progression, with emphasis on lectin complement pathway genes. Decreased and increased patient serum protein levels were associated with susceptibility to CD and Visceral Leishmaniasis, respectively.

Conclusion

This systematic review shows the influence of genetic alterations in complement genes on the progression of several infectious diseases, with a focus on conditions caused by trypanosomatids, and contributes suggestions and evidence to improve experimental design in future research proposals.

Treatment With Suboptimal Dose of Benznidazole Mitigates Immune Response Molecular Pathways in Mice With Chronic Chagas Cardiomyopathy

Chronic Chagas cardiomyopathy (CCC) is the most frequent and severe form of Chagas disease, a neglected tropical illness caused by the protozoan Trypanosoma cruzi, and the main cause of morbimortality from cardiovascular problems in endemic areas. Although efforts have been made to understand the signaling pathways and molecular mechanisms underlying CCC, the immunological signaling pathways regulated by the etiological treatment with benznidazole (Bz) has not been reported. In experimental CCC, Bz combined with the hemorheological and immunoregulatory agent pentoxifylline (PTX) has beneficial effects on CCC. To explore the molecular mechanisms of Bz or Bz+PTX therapeutic strategies, C57BL/6 mice chronically infected with the T. cruzi Colombian strain (discrete typing unit TcI) and showing electrocardiographic abnormalities were submitted to suboptimal dose of Bz or Bz+PTX from 120 to 150 days postinfection. Electrocardiographic alterations, such as prolonged corrected QT interval and heart parasite load, were beneficially impacted by Bz and Bz+PTX. RT-qPCR TaqMan array was used to evaluate the expression of 92 genes related to the immune response in RNA extracted from heart tissues. In comparison with non-infected mice, 30 genes were upregulated, and 31 were downregulated in infected mice. Particularly, infection upregulated the cytokines IFN-γ, IL-12b, and IL-2 (126-, 44-, and 18-fold change, respectively) and the T-cell chemoattractants CCL3 and CCL5 (23- and 16-fold change, respectively). Bz therapy restored the expression of genes related to inflammatory response, cellular development, growth, and proliferation, and tissue development pathways, most probably linked to the cardiac remodeling processes inherent to CCC, thus mitigating the Th1-driven response found in vehicle-treated infected mice. The combined Bz+PTX therapy revealed pathways related to the modulation of cell death and survival, and organismal survival, supporting that this strategy may mitigate the progression of CCC. Altogether, our results contribute to the better understanding of the molecular mechanisms of the immune response in the heart tissue in chronic Chagas disease and reinforce that parasite persistence and dysregulated immune response underpin CCC severity. Therefore, Bz and Bz+PTX chemotherapies emerge as tools to interfere in these pathways aiming to improve CCC prognosis.

Genetically Determined MBL Deficiency Is Associated with Protection against Chronic Cardiomyopathy in Chagas Disease

Chagas disease (CD) is caused by Trypanosoma cruzi, whose sugar moieties are recognized by mannan binding lectin (MBL), a soluble pattern-recognition molecule that activates the lectin pathway of complement. MBL levels and protein activity are affected by polymorphisms in the MBL2 gene. We sequenced the MBL2 promoter and exon 1 in 196 chronic CD patients and 202 controls. The MBL2*C allele, which causes MBL deficiency, was associated with protection against CD (P = 0.007, OR = 0.32). Compared with controls, genotypes with this allele were completely absent in patients with the cardiac form of the disease (P = 0.003). Furthermore, cardiac patients with genotypes causing MBL deficiency presented less heart damage (P = 0.003, OR = 0.23), compared with cardiac patients having the XA haplotype causing low MBL levels, but fully capable of activating complement (P = 0.005, OR = 7.07). Among the patients, those with alleles causing MBL deficiency presented lower levels of cytokines and chemokines possibly implicated in symptom development (IL9, p = 0.013; PDGFB, p = 0.036 and RANTES, p = 0.031). These findings suggest a protective effect of genetically determined MBL deficiency against the development and progression of chronic CD cardiomyopathy.

Chagas disease is considered an important neglected tropical disease, affecting approximately ten million people in Latin America. Although most infected individuals remain asymptomatic, one third of patients develop a chronic heart disease, with progressive inflammation, increase of myocardium, arrhythmia, cardiac insufficiency and heart failure. To date, there is no available marker to indicate the progression neither to determinate the severity of heart damage. Mannan binding lectin (MBL) is an important protein of the immune system able to recognize specific regions on the microorganism surfaces (including Trypanosoma cruzi, the causal agent of Chagas disease) which activate the complement system, a crucial mechanism of the effector immunity. MBL levels and protein activity are affected by genetic differences, named polymorphisms, in the MBL2 gene. This is the first Brazilian study with MBL2 polymorphisms in chronic Chagas disease. We sequenced two regions of MBL2 gene in 196 patients and 202 controls. We found that a polymorphism associated with deficient complement activation protects against Chagas disease and patients with deficiency-associated genotypes presented less echocardiographic alterations. Among the patients, those with alleles causing MBL deficiency presented lower levels of cytokines and chemokines possibly implicated in symptom development (IL9, p = 0.013; PDGFB, p = 0.036 and RANTES, p = 0.031). These findings lead us to suggest that genetically determined MBL deficiency plays a protective role against the development and progression of chronic Chagas disease.

BF*F allotype of the alternative pathway of complement: A marker of protection against the development of antiphospholipid antibodies in patients with systemic lupus erythematosus

Background

B factor (BF) from the alternative complement pathway seems to participate in the pathophysiology of systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS).

Objective

To study the allotypic variability of BF in SLE and their associations with clinical and autoantibodies profile.

Methods

BF allotypes were determined by high-voltage agarose gel electrophoresis, under constant cooling, followed by immunofixation with anti-human BF antibody, in 188 SLE patients and 103 controls. Clinical and serological data were obtained from medical examination and records.

Results

No significant differences of BF variants between patients and controls were found, neither in relation to epidemiologic or clinical manifestations. Associations of phenotype BF SS07 and allotype BF*S07 were found with anticardiolipin IgM (aCl-IgM) antibodies ( p = 0.014 and p = 0.009 respectively), but not with aCl-IgG, lupus anticoagulant (LA), anti β2GPI or clinical APS. A significant decrease in BF*F allotype ( p = 0.043) and BF SF phenotype ( p = 0.018) was detected in patients with anti-phospholipid antibodies as a whole (aCl-IgG, aCl-IgM, LA and anti β2GPI).

Conclusions

There is a link between phenotype BF SS07 and allotype BF*S07 with aCl-IgM in SLE patients; BF*F allotype could be considered a marker of protection against the development of antiphospholipid antibodies in these patients.

Genomic aspects of age-related macular degeneration

Age-related macular degeneration (AMD) is a major late-onset posterior eye disease that causes central vision to deteriorate among elderly populations. The predominant lesion of AMD is the macula, at the interface between the outer retina and the inner choroid. Recent advances in genetics have revealed that inflammatory and angiogenic pathways play critical roles in the pathophysiology of AMD. Genome-wide association studies have identified ARMS2/HTRA1 and CFH as major AMD susceptibility genes. Genetic studies for AMD will contribute to the prevention of central vision loss, the development of new treatment, and the maintenance of quality of vision for productive aging.

Polymorphism of C3 complement in association with myocardial infarction in a sample of central Tunisia

Background

Myocardial infarction (MI) is a major clinical problem because of its large contribution to mortality. The genetic bases of this disease have been widely studied in recent years to find a clear association with some genetic markers that increase the risk of its occurrence. In the present investigation, the correlation between MI and the C3 complement polymorphism was analyzed using a case–control study.

Methods

Our study ported on one hundred seventy survived myocardial infarction patients and ninety five healthy controls. The C3 allele identification was investigated using the amplification refractory mutation system PCR to determine the C3*S and the C3*F alleles of the C3 polymorphism.

Results

Frequencies of C3*S and C3*F in patients are 0.59 and 0.41 respectively. Fisher test results showed a significant increase of C3*F allele in the sample of patients (0.41; odds ratio: 2.616; C.I [1.738-3.938]) compared to controls (0.21; odds ratio: 0.382; 95% CI [0.254-0.575]), p = 2.742 × 10^-6.

Conclusion

A strong positive correlation was found between C3 polymorphism and MI estimating that the risk of myocardial infarction is significantly increased among patients with C3*F allele of this polymorphism.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1190484203893646

Association of L-ficolin levels and FCN2 genotypes with chronic Chagas disease

BACKGROUND

L-ficolin (encoded by FCN2) binds to acetylated sugar moieties of many pathogens, including Trypanosoma cruzi, promoting their phagocytosis and lysis by the complement system.

METHODS

We investigated L-ficolin levels in 160 T. cruzi infected patients with chronic Chagas disease and 71 healthy individuals, and FCN2 polymorphisms (-986 G>A, -602 G>A, and -4 A>G in the promoter and A258S in exon 8) in 243 patients, being 88 indeterminate (asymptomatic), 96 with cardiac, 23 with digestive and 33 with cardiodigestive manifestations (two were unspecified) and 305 controls (135 for A258S).

RESULTS

Patients presented lower L-ficolin plasma levels than controls (p<0.0001). Among the different groups of cardiac commitment, individuals with moderate forms had higher L-ficolin levels than the severe forms (P = 0.039). Lower L-ficolin levels were found associated with the 258S variant in the patients (P = 0.034). We found less -4A/G heterozygotes in the cardiac patients, than in the controls (OR = 0.56 [95% CI = 0.33-0.94], P = 0.034). Heterozygote -4A/G genotypes with the 258S variant and 258SS homozygotes were nevertheless more frequent among cardiodigestive patients than in controls (OR = 14.1 [95% CI = 3.5-56.8], P = 0.0001) and in indeterminate patients (OR = 3.2 [95% CI = 1.1-9.4], P = 0.037). We also found an association of the allelic frequency of the 258S variant with cardiodigestive Chagas disease compared to controls (OR = 2.24 [95% CI = 1.1-4.5], P = 0.037). Thus, decreased patient levels of L-ficolin reflect not only protein consumption due to the disease process, but also the higher frequency of the 258S variant in patients with cardiodigestive symptoms.

CONCLUSION

The very first study on Brazilian cohort associates both L-ficolin plasma levels and FCN2 variants to Chagas disease and subsequent disease progression. The prognostic value of L-ficolin levels and the FCN2*A258S polymorphism should be further evaluated in other settings.

The complotype: dictating risk for inflammation and infection

Complement is a key component of immune defence against infection; it potently drives inflammation at sites of pathology and is essential for killing of pathogens. Genetic linkage of common complement polymorphisms to disease has advanced the concept that subtle changes in complement activity significantly affect disease risk. Functional analyses of disease-linked polymorphic variants demonstrate that, although individual polymorphisms cause only small changes in activity, when combined, the aggregate effects are large. The inherited set of common variants, the complotype, thus has a major impact on susceptibility to inflammatory and infectious diseases. Assessing the complotype of an individual will aid prediction of disease risk and inform intervention to reduce or eliminate risk.

Common polymorphisms in C3, factor B, and factor H collaborate to determine systemic complement activity and disease risk

Common polymorphisms in complement alternative pathway (AP) proteins C3 (C3(R102G)), factor B (fB(R32Q)), and factor H (fH(V62I)) are associated with age-related macular degeneration (AMD) and other pathologies. Our published work showed that fB(R32Q) influences C3 convertase formation, whereas fH(V62I) affects factor I cofactor activity. Here we show how C3(R102G) (C3S/F) influences AP activity. In hemolysis assays, C3(102G) activated AP more efficiently (EC(50) C3(102G): 157 nM; C3(102R): 191 nM; P < 0.0001). fB binding kinetics and convertase stability were identical, but native and recombinant fH bound more strongly to C3b(102R) (K(D) C3b(102R): 1.0 μM; C3b(102G): 1.4 μM; P < 0.0001). Accelerated decay was unaltered, but fH cofactor activity was reduced for C3b(102G), favoring AP amplification. Combining disease "risk" variants (C3(102G), fB(32R), and fH(62V)) in add-back assays yielded sixfold higher hemolytic activity compared with "protective" variants (C3(102R), fB(32Q), and fH(62I); P < 0.0001). These data introduce the concept of a functional complotype (combination of polymorphisms) defining complement activity in an individual, thereby influencing susceptibility to AP-driven disease.

MASP2 haplotypes are associated with high risk of cardiomyopathy in chronic Chagas disease

Mannose-binding lectin (MBL) initiates complement on Trypanosoma cruzi through the MBL-associated serine protease 2 (MASP2). We haplotyped six MASP2 polymorphisms in 208 chronic chagasic patients, being 81 indeterminate and 123 symptomatic (76 with cardiac, 19 with digestive and 28 with cardiodigestive forms) and 300 healthy individuals from Southern Brazil, using PCR with sequence-specific primers. The g.1961795C, p.371D diplotype (short CD) occurred at a higher frequency among symptomatic patients, compared with the indeterminate group (P(Bf)=0.012, OR=3.11), as well as genotypes with CD, but not with the g.1945560A in the promoter in cardiac patients (P(Bf)=0.012, OR=13.54). CD haplotypes linked to the p.P126L and p.V377A variants were associated with reduced MASP-2 levels (P<0.0001) but not reduced MBL/MASP-2/C4 complexes. MASP2*CD genotypes, most of them generating low MASP-2 levels, are associated with high risk of chagasic cardiomyopathy. Rapid MASP2 genotyping might be used to predict the risk of symptomatic disease.

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.

Association of the macrophage migration inhibitory factor -173G/C polymorphism with Chagas disease

Our aim was to evaluate the association of functional polymorphism of macrophage migration inhibitory factor (MIF) gene with Chagas disease. Our study includes two independent cohorts: 240 chagasic patients and 199 controls from Colombia; and 74 chagasic patients and 85 controls from Peru. The single nucleotide polymorphism (SNP) -173 G/C of MIF gene was determined using a polymerase chain reaction (PCR) system with pre-developed TaqMan assay. We observed a statistically significant difference in the distribution of -173*C allele of MIF gene between patients and controls in the Colombian cohort (OR = 1.6, 95% CI = 1.12-2.18, p = 0.006). Similar association was found in the Peruvian cohort (OR = 2.4, 95% CI = 1.31-4.38, p = 0.003). A meta-analysis of the Colombian and Peruvian cohorts demonstrated that the -173 C allele confers a risk effect in chagasic patients (pooled OR = 1.75, 95% CI = 1.30-2.33, p = 0.0002). In addition, a gene dose of the MIF -173 C allele was observed (pooled OR = 4.01, 95% CI = 1.25-12.85, p = 0.004). Our results suggest that the MIF -173G/C polymorphism confers susceptibility to Chagas disease in the populations under study.

Functional basis of protection against age-related macular degeneration conferred by a common polymorphism in complement factor B

Mutations and polymorphisms in complement genes have been linked with numerous rare and prevalent disorders, implicating dysregulation of complement in pathogenesis. The 3 common alleles of factor B (fB) encode Arg (fB(32R)), Gln (fB(32Q)), or Trp (fB(32W)) at position 32 in the Ba domain. The fB(32Q) allele is protective for age-related macular degeneration, the commonest cause of blindness in developed countries. Factor B variants were purified from plasma of homozygous individuals and were tested in hemolysis assays. The protective variant fB(32Q) had decreased activity compared with fB(32R). Biacore comparison revealed markedly different proenzyme formation; fB(32R) bound C3b with 4-fold higher affinity, and formation of activated convertase was enhanced. Binding and functional differences were confirmed with recombinant fB(32R) and fB(32Q); an intermediate affinity was revealed for fB(32W). To confirm contribution of Ba to binding, affinity of Ba for C3b was determined. Ba-fB(32R) had 3-fold higher affinity compared with Ba-fB(32Q). We demonstrate that the disease-protective effect of fB(32Q) is consequent on decreased potential to form convertase and amplify complement activation. Knowledge of the functional consequences of polymorphisms in complement activators and regulators will aid disease prediction and inform targeting of diagnostics and therapeutics.

Evaluation of clustering and genotype distribution for replication in genome wide association studies: the age-related eye disease study

Genome-wide association studies (GWASs) assess correlation between traits and DNA sequence variation using large numbers of genetic variants such as single nucleotide polymorphisms (SNPs) distributed across the genome. A GWAS produces many trait-SNP associations with low p-values, but few are replicated in subsequent studies. We sought to determine if characteristics of the genomic loci associated with a trait could be used to identify initial associations with a higher chance of replication in a second cohort. Data from the age-related eye disease study (AREDS) of 100,000 SNPs on 395 subjects with and 198 without age-related macular degeneration (AMD) were employed. Loci highly associated with AMD were characterized based on the distribution of genotypes, level of significance, and clustering of adjacent SNPs also associated with AMD suggesting linkage disequilibrium or multiple effects. Forty nine loci were highly associated with AMD, including 3 loci (CFH, C2/BF, LOC387715/HTRA1) already known to contain important genetic risks for AMD. One additional locus (C3) reported during the course of this study was identified and replicated in an additional study group. Tag-SNPs and haplotypes for each locus were evaluated for association with AMD in additional cohorts to account for population differences between discovery and replication subjects, but no additional clearly significant associations were identified. Relying on a significant genotype tests using a log-additive model would have excluded 57% of the non-replicated and none of the replicated loci, while use of other SNP features and clustering might have missed true associations.

Polymorphisms of toll-like receptor 2 and 4 genes in Chagas disease

The aim of this study was to test the possible implication of toll-like receptor 2 (TLR2) and TLR4 gene polymorphisms in determining the susceptibility to Chagas' disease. Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism in 475 individuals from Colombia, 143 seropositive with chagasic cardiomyopathy, 132 seropositive asymptomatic and 200 seronegative. The TLR2 arginine to glutamine substitution at residue 753(Arg753Gln) polymorphism was absent in the groups analyzed. The TLR4 Asp299Gly and Thr399Ile polymorphisms are in linkage disequilibrium and we observed a very low frequency of these polymorphisms in our study population (2.6% and 1.8% respectively). The overall TLR2 and TLR4 alleles and genotype distribution in seronegative and seropositive were not significantly different. We compared the frequencies between asymptomatic patients and those with chagasic cardiomyopathy and we did not observe any significant differences in the distribution of alleles or genotypes. In summary, this study corroborates the low frequency of TLR2 and TLR4 polymorphisms observed in other populations and suggest that these do not play an important role in Chagas' disease. The validation of these findings in independent cohorts is needed to firmly establish a role for TLR2 and TLR4 variants in Chagas' disease.

Interleukin-1 gene cluster polymorphism in chagas disease in a Colombian case-control study

The aim of this study was to assess the possible association between the IL1A, IL1B and IL1RN gene polymorphisms and Chagas disease. Our study population consisted of 130 serologically positive cardiomyopathic patients and 130 seropositive and asymptomatic individuals from a Colombian population where Trypanosoma cruzi infection is endemic. Genotyping of the IL1A (-889C/T, +4845G/T), IL1B (-511C/T, -31T/C, +3954T/C, +5810G/A) and IL1RN (+8006T/C, +8061C/T, +11100T/C) polymorphisms was performed by polymerase chain reaction-restriction fragment length polymorphism and polymerase chain reaction sequence-specific primer methods. Statistically significant differences in the distribution of the IL1B +5810 genotypes were observed comparing cardiomyopathic patients and asymptomatic individuals (p = 0.036). Frequency of the GG genotype was higher in the cardiomyopathic patient group than in the asymptomatic group (13% versus 5%, p = 0.03, odds ratio [OR] = 2.64, 95% confidence interval [CI] = 0.99-7.33). Differences in the distribution of the allele frequencies were also observed, being the +5810G allele overrepresented in patients with cardiomyopathy (37% versus 27%, p = 0.014, OR = 1.59, 95% CI = 1.08-2.36). Examination of markers in the IL1A (-889 and +4845), IL1B (-511, -31, and +3954) and IL1RN (+11100) genes revealed that the overall distribution of alleles and genotypes in patients with chagasic cardiomyopathy and asymptomatic were not significantly different. Our results show that in Colombian population the IL1B+5810G allele was associated with an increased risk chagasic cardiomyopathy. In addition, we demonstrated that homozygosity for the IL1B +5810G risk allele increased significantly the susceptibility to cardiomyopathy. This implies that the effect of IL1B gene on chagasic cardiomyopathy predisposition is dose dependent. We found that the haplotype CT of IL1B -31 and +3954 polymorphisms showed higher association with risk to chagasic cardiomyopathy (p(c) = 0.008, OR = 12.53) and the extended haplotype (CCTCATT) was significantly more frequent in asymptomatic than in cardiomyopathic patients (p = 0.0014, p(c) = 0.011, OR = 0.17). Therefore this study suggests that IL1 gene cluster polymorphisms may play a relevant role in the susceptibility to development of chagasic chronic cardiomyopathy.