Pathological manifestations in lymphatic filariasis correlate with lack of inhibitory properties of IgG4 antibodies on IgE-activated granulocytes

Brugia malayi filarial helminth-derived extracellular vesicles suppress antigen presenting cell function and antigen-specific CD4+ T cell responses

Introduction

Live microfilariae (mf) and mf-derived extracellular vesicles (EVs) have been shown to modulate human antigen presenting cell (APC) function, most notably by suppressing the induction of IL-12 (and other pro-inflammatory cytokines) following activation with LPS and interferon-y.

Methods

To explore further how EVs alter human APC function, we studied the effect of mf and EVs on human elutriated monocyte-derived dendritic cells (DC) following exposure to Mf, mf-derived excretory/secretory (E/S) products, E/S depleted of EVs through ultracentrifugation and purified EVs.  After demonstrating that the measurable responses induced by live mf could be recapitulated by EVs and EV-containing E/S, we next performed RNAseq analysis of human DC following exposure to live mf, EVs, E/S, or EV-depleted E/S.

Results

In our analyses of the data for the DC, using a false discovery rate (FDR)<0.05, EV-exposed DC had induced the expression of 212 differentially expressed genes (DEGs) when compared to unexposed DC and 157 when compared to E/S-depleted EVs.  These genes were enriched in GO biological processes associated with neutrophil degranulation and 15 DEGs associated with KEGG Lysosome pathways. IPA analysis point to immune dysregulation. We next aimed to understand the intracellular processes altered by EVs and the effect these have on effector T cells. When SARS CoV-2 Membrane-specific CD4+ TCLs were assessed following EV conditioning of autologous DC and activation with the SARS CoV-2-Membrane peptide pool, we found conditioning reduced the frequency of SARS CoV-2 Membrane-specific CD3+ CD4+ CD154+ cells (p=.015). Similarly, EV-conditioning of SARS CoV-2 Membrane-specific CD3+ CD4+ cells induced fewer cell capable of producing IFN-γ (p=.045).

Discussion

Taken together, our data suggest a modulatory role of EVs on APC function that likely leads to defects in T cell effector function.

Unbalanced Arginine pathway and altered maturation of pleural macrophages in Th2-deficient mice during Litomosoides sigmodontis filarial infection

Filarial parasites are tissue dwelling worms transmitted by hematophagous vectors. Understanding the mechanisms regulating microfilariae (the parasite offspring) development is a prerequisite for controlling transmission in filarial infections. Th2 immune responses are key for building efficient anti-parasite responses but have been shown to also lead to detrimental tissue damage in the presence of microfilariae. Litomosoides sigmodontis, a rodent filaria residing in the pleural cavity was therefore used to characterize pleuropulmonary pathology and associated immune responses in wild-type and Th2 deficient mice. Wild-type and Th2-deficient mice (Il-4rα-/-/Il-5-/- ) were infected with L. sigmodontis and parasite outcome was analyzed during the patent phase (when microfilariae are in the general circulation). Pleuropulmonary manifestations were investigated and pleural and bronchoalveolar cells were characterized by RNA analysis, imaging and/or flow cytometry focusing on macrophages. Il-4rα-/-/Il-5-/- mice were hypermicrofilaremic and showed an enhanced filarial survival but also displayed a drastic reduction of microfilaria-driven pleural cavity pathologies. In parallel, pleural macrophages from Il-4rα-/-/Il-5-/- mice lacked expression of prototypical alternative activation markers RELMα and Chil3 and showed an altered balance of some markers of the arginine metabolic pathway. In addition, monocytes-derived F4/80intermediate macrophages from infected Il-4rα-/-/Il-5-/- mice failed to mature into resident F4/80high large macrophages. Altogether these data emphasize that the presence of both microfilariae and IL-4R/IL-5 signaling are critical in the development of the pathology and in the phenotype of macrophages. In Il-4rα-/-/Il-5-/- mice, the balance is in favor of parasite development while limiting the pathology associated with the host immune response.

Helminth antigens differentially modulate the activation of CD4+ and CD8+ T lymphocytes of convalescent COVID-19 patients in vitro

BACKGROUND

The coronavirus disease 2019 (COVID-19) is a respiratory disease caused by SARS-CoV-2, a recently discovered strain of coronavirus. The virus has spread rapidly, causing millions of death worldwide. Contrary to the predictions, prevalence and mortality due to COVID-19 have remained moderate on the African continent. Several factors, including age, genetics, vaccines, and co-infections, might impact the course of the pandemic in Africa. Helminths are highly endemic in Sub-Saharan Africa and are renowned for their ability to evade, skew, and suppress human immune responses through various immune-modulatory mechanisms. Such effects will likely impact SARS-CoV-2 transmission and disease progression.

METHODS

Here, we analyzed in vitro the impact of antigen extracts from three major helminth parasites, including Onchocerca volvulus, Brugia malayi, and Ascaris lumbricoides, on the immune reactivity to SARS-CoV-2 peptides in COVID-19 patients. Activation of CD4⁺ and CD8⁺ T cells was investigated using flow cytometry to monitor the expression of CD137 (4-1BB) and CD69. Cytokine expression, including IL-6, IL-10, IFN-γ, and TNFα, was measured by Luminex in cell culture supernatants.

RESULTS

We observed that helminth antigens significantly reduced the frequency of SARS-CoV-2-reactive CD4⁺ T helper cells. In contrast, the expression of SARS-CoV-2-reactive CD8⁺ T cells was not affected and even significantly increased when PBMCs from COVID-19 patients living in Benin, an endemic helminth country, were used. In addition, stimulation with helminth antigens was associated with increased IL-10 and a reduction of IFNγ and TNFα.

CONCLUSIONS

Our data offer a plausible explanation for the moderate incidence of COVID-19 in Africa and support the hypothesis that helper T cell-mediated immune responses to SARS-CoV-2 are mitigated in the presence of helminth antigens, while virus-specific cytotoxic T cell responses are maintained.

Immunoreactivity of Brugia malayi Calreticulin and Its Domains with Sera of Different Categories of Bancroftian Filarial Patients

PURPOSE

We identified calreticulin in human filaria Brugia malayi (BmCRT) that shares 97% homology with Wuchereria bancrofti calreticulin (WbCRT), but only 56% with human calreticulin. We found that BmCRT binds C1q and prevents complement-mediated parasite death; immunization with BmCRT leads to parasite death in a rodent model of the infection. BmCRT could, therefore, be a potential vaccine candidate. In the present study, we determined the levels of BmCRT-reactive IgG and its isotype in bancroftian filarial subjects.

METHODS

Recombinant BmCRT (rBmCRT) was prepared, and the sera of endemic normal subjects (EN), microfilaraemics (Mf+) and chronic amicrofilaraemics (ChMf-) from a bancroftian filaria-endemic area and normal subjects from filaria-non-endemic area (NEN) were probed for IgG and its isotypes reacting with rBmCRT and its domains rN, rP and rC.

RESULTS

rBmCRT and its rN domain-reactive IgG levels were high in EN and Mf+ groups; rC domain and rP domain showed moderate and very little reactivity, respectively. NEN sera were non-reactive. Moderate levels of rBmCRT-reactive IgG1, IgG3 and IgG4 in EN and Mf+ groups and low levels of IgG2 in Mf+ were found; IgG1 and IgG3 reactivity was found for rBmCRT and its rN domain only, while IgG4 reactivity was moderate for rN domain and low for rP and rC domains. While IgG reactivity was seen in all the endemic subjects, IgG isotype reactivity was found mostly in EN and Mf+ subjects.

CONCLUSIONS

Moderate levels of rBmCRT (and its rN domain)-reactive IgG and its isotypes are present in bancroftian subjects. Preponderance of IgG1 and IgG3 isotypes which bind and activate complement has relevance to vaccine potential of BmCRT.

Underlying Co-Morbidity Reveals Unique Immune Signatures in Type II Diabetes Patients Infected With SARS-CoV2

Background

SARS-CoV2 infection in patients with comorbidities, particularly T2DM, has been a major challenge globally and has been shown to be associated with high morbidity and mortality. Here, we did whole blood immunophenotyping along with plasma cytokine, chemokine, antibody isotyping, and viral load from oropharyngeal swab to understand the immune pathology in the T2DM patients infected with SARS-CoV2.

Methods

Blood samples from 25 Covid-19 positive patients having T2DM, 10 Covid-19 positive patients not having T2DM, and 10 Covid-19 negative, non-diabetic healthy controls were assessed for various immune cells by analyzing for their signature surface proteins in mass cytometry. Circulating cytokines, chemokines, and antibody isotypes were determined from plasma while viral copy number was determined from oropharyngeal swabs. All our representative data corroborated with laboratory findings.

Results

Our observations encompass T2DM patients having elevated levels of both type I and type II cytokines and higher levels of circulating IgA, IgM, IgG1, and IgG2 as compared to NDM and healthy volunteers. They also displayed higher percentages of granulocytes, mDCs, plasmablasts, Th2-like cells, CD4⁺ EM cells, and CD8⁺ TE cells as compared to healthy volunteers. T2DM patients also displayed lower percentages of pDCs, lymphocytes, CD8⁺ TE cells, CD4⁺, and CD8⁺ EM.

Conclusion

Our study demonstrated that patients with T2DM displayed higher inflammatory markers and a dysregulated anti-viral and anti-inflammatory response when compared to NDM and healthy controls and the dysregulated immune response may be attributed to meta inflammation.

Distinct N-Linked Immunoglobulin G Glycosylation Patterns Are Associated With Chronic Pathology and Asymptomatic Infections in Human Lymphatic Filariasis

Lymphatic filariasis presents a complex spectrum of clinical manifestations ranging from asymptomatic microfilariaemic (MF+) to chronic pathology (CP), including lymphedema and elephantiasis. Emerging evidence suggests a link between the physiopathology of filarial infections and antibody properties. Post-translational glycosylation has been shown to play a key role in the modulation of antibodies’ effector functions. Here, we investigated the link between total IgG-N-glycosylation patterns and the physiopathology of human lymphatic filariasis using UPLC-FLD/ESI-MS comparison of N-glycan profiles of total IgG purified from endemic normals (EN), MF+, and CP patients. We detected a total of 19 glycans released from all IgG samples. Strikingly, agalactosylated glycan residues were more prominent in EN, whereas sialylation and bisecting GlcNac correlated with asymptomatic infections. While IgG from all three clinical groups expressed high levels of fucosylated residues, significantly lower expressions of afucosylated IgG were seen in MF+ individuals compared to EN and CP. Our data reveal distinct N-linked IgG glycan profiles in EN, MF+, and CP and suggest that IgG galactosylation and sialylation are associated with chronic pathology, whereas agalactosylation correlates with putative immunity. The results also indicate a role for sialylation, fucosylation, and bisecting GlcNac in immune tolerance to the parasite. These findings highlight the link between N-glycosylation and the physiopathology of lymphatic filariasis and open new research avenues for next-generation therapeutic formulations against infectious diseases.

Adoptive Transfer of Immune Cells Into RAG2IL-2Rγ-Deficient Mice During Litomosoides sigmodontis Infection: A Novel Approach to Investigate Filarial-Specific Immune Responses

Despite long-term mass drug administration programmes, approximately 220 million people are still infected with filariae in endemic regions. Several research studies have characterized host immune responses but a major obstacle for research on human filariae has been the inability to obtain adult worms which in turn has hindered analysis on infection kinetics and immune signalling. Although the Litomosoides sigmodontis filarial mouse model is well-established, the complex immunological mechanisms associated with filarial control and disease progression remain unclear and translation to human infections is difficult, especially since human filarial infections in rodents are limited. To overcome these obstacles, we performed adoptive immune cell transfer experiments into RAG2IL-2Rγ-deficient C57BL/6 mice. These mice lack T, B and natural killer cells and are susceptible to infection with the human filaria Loa loa. In this study, we revealed a long-term release of L. sigmodontis offspring (microfilariae) in RAG2IL-2Rγ-deficient C57BL/6 mice, which contrasts to C57BL/6 mice which normally eliminate the parasites before patency. We further showed that CD4⁺ T cells isolated from acute L. sigmodontis-infected C57BL/6 donor mice or mice that already cleared the infection were able to eliminate the parasite and prevent inflammation at the site of infection. In addition, the clearance of the parasites was associated with Th17 polarization of the CD4⁺ T cells. Consequently, adoptive transfer of immune cell subsets into RAG2IL-2Rγ-deficient C57BL/6 mice will provide an optimal platform to decipher characteristics of distinct immune cells that are crucial for the immunity against rodent and human filarial infections and moreover, might be useful for preclinical research, especially about the efficacy of macrofilaricidal drugs.

Evaluation of Rapid IgG4 Test for Diagnosis of Gnathostomiasis

Human gnathostomiasis is a parasitic disease caused by Gnathostoma nematode infection. A rapid, reliable, and practical immunoassay, named dot immuno-gold filtration assay (DIGFA), was developed to supporting clinical diagnosis of gnathostomiasis. The practical tool detected anti-Gnathostoma-specific IgG4 in human serum using crude extract of third-stage larvae as antigen. The result of the test was shown by anti-human IgG4 monoclonal antibody conjugated colloidal gold. The sensitivity and specificity of the test were both 100% for detection in human sera from patients with gnathostomiasis (13/13) and from healthy negative controls (50/50), respectively. Cross-reactivity with heterogonous serum samples from patients with other helminthiases ranged from 0 (trichinosis, paragonimiasis, clonorchiasis, schistosomiasis, and cysticercosis) to 25.0% (sparganosis), with an average of 6.3% (7/112). Moreover, specific IgG4 antibodies diminished at 6 months after treatment. This study showed that DIGFA for the detection of specific IgG4 in human sera could be a promising tool for the diagnosis of gnathostomiasis and useful for evaluating therapeutic effects.

Development of Immunochromatographic Test Kit for Rapid Detection of Specific IgG4 Antibody in Whole-Blood Samples for Diagnosis of Human Gnathostomiasis

Human gnathostomiasis is a harmful food-borne zoonosis caused by roundworms of the genus Gnathostoma. The parasite can occasionally migrate to the central nervous system, causing life-threatening disease and death. Here, we report a new point-of-care (POC) test kit, the gnathostomiasis blood immunochromatographic test (GB-ICT) kit. The kit is based on recombinant Gnathostoma spinigerum antigen and detects specific IgG4 antibody in whole-blood samples (WBSs). The GB-ICT kit showed potentially high diagnostic values with simulated WBSs (n = 248), which were obtained by spiking patients’ sera with red blood cells. The accuracy, sensitivity, specificity, and positive and negative predictive values were 95.2%, 100%, 93.8%, 81.5%, and 100%, respectively. Ten WBSs from clinically suspected gnathostomiasis patients were all positive according to the GB-ICT kit, while 10 WBSs from healthy volunteers were negative. The GB-ICT kit is a simple and convenient POC testing tool using finger-prick blood samples: venous blood sampling and serum separation processes are not required. The GB-ICT kit can support clinical diagnosis in remote areas and field settings without sophisticated equipment facilities.

An Insight into the Discovery of Potent Antifilarial Leads Against Lymphatic Filariasis

BACKGROUND AND OBJECTIVES

Lymphatic filariasis is a neglected tropical disease caused by infection with filarial worms that are transmitted through mosquito bites. Globally, 120 million people are infected, with nearly 40 million people disfigured and disabled by complications such as severe swelling of the legs (elephantiasis) or scrotum (hydrocele). Current treatments (ivermectin, diethylcarbamazine) have limited effects on adult parasites and produce side effects; therefore, there is an urgent to search for new antifilarial agents. Numerous studies on the antifilarial activity of pure molecules have been reported accross the recent literature. The present study describes the current standings of potent antifilarial compounds against lymphatic filariasis.

METHODS

A literature search was conducted for naturally occurring and synthetic antifilarial compounds by referencing textbooks and scientific databases (SciFinder, PubMed, Science Direct, Wiley, ACS, SciELO, Google Scholar, and Springer, among others) from their inception until September 2019.

RESULTS

Numerous compounds have been reported to exhibit antifilarial acitivity in adult and microfilariae forms of the parasites responsible for lymphatic filariasis. In silico studies of active antifilarial compounds (ligands) showed molecular interactions over the protein targets (trehalose-6-phosphate phosphatase, thymidylate synthase, among others) of lymphatic filariasis, and supported the in vitro results.

CONCLUSION

With reference to in vitro antifilarial studies, there is evidence that natural and synthetic products can serve as basic scaffolds for the development of antifilarial agents. The optimization of the most potent antifilarial compounds can be further performed, followed by their in vivo studies.

IgG4 antibodies from patients with asymptomatic bancroftian filariasis inhibit the binding of IgG1 and IgG2 to C1q in a Fc-Fc-dependent mechanism

A striking feature of lymphatic filariasis (LF) is the clinical heterogeneity among exposed individuals. While endemic normals (EN) remain free of infection despite constant exposure to the infective larvae, a small group of patients, generally microfilaria free (Mf-) develops severe pathology (CP) such as lymphedema or hydrocele. Another group of infected individuals remains asymptomatic while expressing large amounts of microfilariae (Mf+). This Mf+ group is characterized by an immune-suppressed profile with high levels of anti-inflammatory cytokines and elevated IgG4. This particular immunoglobulin is unable to activate the complement. The complement system plays a critical role in both innate and adaptive immunity. However, its importance and regulation during LF is not fully understood. Using affinity chromatography and solid-phase-enzyme-immunoassays, we investigated the ability of antibody isotypes from LF clinical groups to bind C1q, the first element of the complement’s classical pathway. The results indicate that while C1q is similarly expressed in all LF clinical groups, IgG1–2 in the plasma from Mf+ individuals presented significantly lower affinity to C1q compared to EN, Mf−, and CP. In addition, selective depletion of IgG4 significantly enhanced the affinity of IgG1–2 to C1q in Mf+ individuals. Strikingly, no effect was seen on the ability of IgG3 to bind C1q in the same conditions. More interestingly, papain-generated IgG4-Fc-portions interacted with Fc portions of IgG1–2 as revealed by far-western blot analysis. These data suggest that while being unable to bind C1q, IgG4 inhibits the first steps of the complement classical pathway by IgG1 or IgG2 via Fc-Fc interactions.

Correlation of Lyme Disease-Associated IgG4 Autoantibodies With Synovial Pathology in Antibiotic-Refractory Lyme Arthritis

OBJECTIVE

To determine whether IgG subclasses of Borrelia burgdorferi antibodies differ from those of 3 Lyme disease (LD)-associated autoantibodies.

METHODS

IgG antibody subclasses were determined by enzyme-linked immunosorbent assay in serum samples from 215 patients with features representative of each of the 3 stages of LD. Antibody and cytokine profiles were measured in matched serum and synovial fluid (SF) samples from patients with Lyme arthritis. Synovial tissue from patients with antibiotic-refractory arthritis was examined for histologic features, IgG subclasses of plasma cells, and messenger RNA (mRNA) subclass expression.

RESULTS

B burgdorferi antibodies were primarily of the IgG1 and IgG3 subclasses, and the levels increased as the infection progressed. In contrast, LD-associated autoantibodies were mainly of the IgG2 and IgG4 subclasses, and these responses were found primarily in patients with either antibiotic-refractory or antibiotic-responsive arthritis, particularly in SF. However, compared with the responsive group, the inflammatory milieu in SF in the refractory group was enriched for cytokines representative of innate, Th1, Th2, and Th17 responses. Synovial tissue in a subgroup of patients with refractory arthritis showed marked expression of mRNA for IgG4 antibodies and large numbers of IgG4-staining plasma cells. IgG4 autoantibodies in SF to each of the 3 LD-associated autoantigens correlated with the magnitude of obliterative microvascular lesions and fibrosis in the tissue.

CONCLUSION

Our findings indicate that the subclasses of IgG antibodies to B burgdorferi differ from those of LD-associated autoantibodies. Furthermore, the correlation of IgG4 autoantibodies with specific synovial pathology in the refractory group suggests a role for these autoantibodies, either protective or pathologic, in antibiotic-refractory Lyme arthritis.

Trichinella spiralis Infection Mitigates Collagen-Induced Arthritis via Programmed Death 1-Mediated Immunomodulation

Helminth infection induces Th2-biased immune responses and inhibitory/regulatory pathways that minimize excessive inflammation to facilitate the chronic infection of helminth in the host and in the meantime, prevent host hypersensitivity from autoimmune or atopic diseases. However, the detailed molecular mechanisms behind modulation on inflammatory diseases are yet to be clarified. Programmed death 1 (PD-1) is one of the important inhibitory receptors involved in the balance of host immune responses during chronic infection. Here, we used the murine model to examine the role of PD-1 in CD4+ T cells in the effects of Trichinella spiralis infection on collagen-induced arthritis (CIA). Mice infected with T. spiralis demonstrated higher expression of PD-1 in the spleen CD4+ T cells than those without infection. Mice infected with T. spiralis 2 weeks prior to being immunized with type II collagen displayed lower arthritis incidence and significantly attenuated pathology of CIA compared with those of uninfected mice. The therapeutic effect of T. spiralis infection on CIA was reversed by blocking PD-1 with anti-PD-1 antibody, associated with enhanced Th1/Th17 pro-inflammatory responses and reduced Th2 responses. The role of PD-1 in regulating CD4+ T cell differentiation and proliferation during T. spiralis infection was further examined in PD-1 knockout (PD-1-/-) C57BL/6 J mice. Interestingly, T. spiralis-induced alteration of attenuated Th1 and enhanced Th2/regulatory T cell differentiation in wild-type (WT) mice was effectively diminished in PD-1-/- mice characterized by recovered Th1 cytokine levels, reduced levels of Th2 and regulatory cytokines and CD4+CD25+Foxp3+ cells. Moreover, T. spiralis-induced CD4+ T cell proliferation suppression in WT mice was partially restored in PD-1-/- mice. This study introduces the first evidence that PD-1 plays a critical role in helminth infection-attenuated CIA in a mouse model by regulating the CD4+ T cell function, which may provide the new insights into the mechanisms of helminth-induced immunomodulation of host autoimmunity.