Human complement receptor 2 (CR2/CD21) as a receptor for DNA: implications for its roles in the immune response and the pathogenesis of systemic lupus erythematosus (SLE)

Unveiling genetic signatures associated with resilience to neonatal diarrhea in lambs through two GWAS approaches

Neonatal diarrhea presents a significant global challenge due to its multifactorial etiology, resulting in high morbidity and mortality rates, and substantial economic losses. While molecular-level studies on genetic resilience/susceptibility to neonatal diarrhea in farm animals are scarce, prior observations indicate promising research directions. Thus, the present study utilizes two genome-wide association approaches, pKWmEB and MLM, to explore potential links between genetic variations in innate immunity and neonatal diarrhea in Karacabey Merino lambs. Analyzing 707 lambs, including 180 cases and 527 controls, revealed an overall prevalence rate of 25.5%. The pKWmEB analysis identified 13 significant SNPs exceeding the threshold of ≥ LOD 3. Moreover, MLM detected one SNP (s61781.1) in the SLC22A8 gene (p-value, 1.85eE-7), which was co-detected by both methods. A McNemar's test was conducted as the final assessment to identify whether there are any major effective markers among the detected SNPs. Results indicate that four markers-oar3_OAR1_122352257, OAR17_77709936.1, oar3_OAR18_17278638, and s61781.1-have a substantial impact on neonatal diarrhea prevalence (odds ratio: 2.03 to 3.10; statistical power: 0.88 to 0.99). Therefore, we propose the annotated genes harboring three of the associated markers, TIAM1, YDJC, and SLC22A8, as candidate major genes for selective breeding against neonatal diarrhea.

Identification of Altered Primary Immunodeficiency-Associated Genes and Their Implications in Pediatric Cancers

BACKGROUND

Cancer is the leading cause of disease-related mortality in children and malignancies are more frequently observed in individuals with primary immunodeficiencies (PIDs). This study aimed to identify and highlight the molecular mechanisms, such as oncogenesis and immune evasion, by which PID-related genes may lead to the development of pediatric cancers.

METHOD

We implemented a novel bioinformatics framework using patient data from the TARGET database and performed a comparative transcriptome analysis of PID-related genes in pediatric cancers between normal and cancer tissues, gene ontology enrichment, and protein-protein interaction analyses, and determined the prognostic impacts of commonly mutated and differentially expressed PID-related genes.

RESULTS

From the Fulgent Genetics Comprehensive Primary Immunodeficiency panel of 472 PID-related genes, 89 genes were significantly differentially expressed between normal and cancer tissues, and 20 genes were mutated in two or more patients. Enrichment analysis highlighted many immune system processes as well as additional pathways in the mutated PID-related genes related to oncogenesis. Survival outcomes for patients with altered PID-related genes were significantly different for 75 of the 89 DEGs, often resulting in a poorer prognosis.

CONCLUSIONS

Overall, multiple PID-related genes demonstrated the connection between PIDs and cancer development and should be studied further, with hopes of identifying new therapeutic targets.

CD11c+ T-bet+ CD21hi B Cells Are Negatively Associated With Renal Impairment in Systemic Lupus Erythematosus and Act as a Marker for Nephritis Remission

Lupus nephritis (LN) is one of the most common manifestations of systemic lupus erythematosus (SLE), characterized by abnormal B cell activation and differentiation to memory or plasma effector cells. However, the role of these cells in the pathogenesis of LN is not fully understood, as well as the effect of induction therapy on B cell subsets, possibly associated with this manifestation, like aged-associated B cells (ABCs). Consequently, we analyzed the molecules defining the ABCs subpopulation (CD11c, T-bet, and CD21) through flow cytometry of blood samples from patients with lupus presenting or not LN, following up a small sub-cohort after six months of induction therapy. The frequency of ABCs resulted higher in LN patients compared to healthy subjects. Unexpectedly, we identified a robust reduction of a CD21^hi subset that was almost specific to LN patients. Moreover, several clinical and laboratory lupus features showed strong and significant correlations with this undefined B cell subpopulation. Finally, it was observed that the induction therapy affected not only the frequencies of ABCs and CD21^hi subsets but also the phenotype of the CD21^hi subset that expressed a higher density of CXCR5. Collectively, our results suggest that ABCs, and more importantly the CD21^hi subset, may work to assess therapeutic response since the reduced frequency of CD21^hi cells could be associated with the onset of LN.

Osteonecrosis in systemic lupus erythematosus: Systematic insight from the epidemiology, pathogenesis, diagnosis and management

Osteonecrosis (ON) is one of the serious and well recognized complicationscausing severe pain and disability in patients with systemic lupus erythematosus (SLE), and its manifestation and pathogenesis are only partially understood. This review provide an update of the recent progress in etiology, pathogenesis, diagnosis, and treatment of systemic lupus erythematosus related osteonecrosis (SLE-ON). Despite the concomitant use of corticosteroids, alcohol and obesity, the dysregulated immune micro-environment and the complex pathogenesis of SLE synergistically play important roles in the development of ON. Osteonecrosis of femoral head (ONFH) is the most often involved joint in SLE. The current classification and staging system of ONFH is based on imaging techniques, particularly relating to MRI and CT, for the identification and quantification of necrotic lesions. For SLE-ONFH patients, both SLE specific clinical symptoms and ONFH imaging findings should be comprehensively evaluated. Even though advances concerning bone grafting and arthroplasty procedures have resulted in improved clinical outcomes, early pharmacological treatment at the pre-collapse stage may prevent joint collapse and reduce the joint arthroplasty rate, and this needs to be accounted. Although some progress has been made, considerably more research is needed before we fully understand SLE-ONFH. Future treatments of SLE-ONFH may involve genetic or cell-based therapies that target potential biomarkers, and this will lead to effective measures for saving thefunction of hip joint and preventing osteonecrosis.

New aspects in the regulation of human B cell functions by complement receptors CR1, CR2, CR3 and CR4

The involvement of complement in the regulation of antibody responses has been known for long. By now several additional B cell functions - including cytokine production and antigen presentation - have also been shown to be regulated by complement proteins. Most of these important activities are mediated by receptors interacting with activation fragments of the central component of the complement system C3, such as C3b, iC3b and C3d, which are covalently attached to antigens and immune complexes. This review summarizes the role of complement receptors interacting with these ligands, namely CR1 (CD35), CR2 (CD21), CR3 (CD11b/CD18) and CR4 (CD11c/CD18) expressed by B cells in health and disease. Although we focus on human B lymphocytes, we also aim to call the attention to important differences between human and mouse systems.

Revisiting the Coreceptor Function of Complement Receptor Type 2 (CR2, CD21); Coengagement With the B-Cell Receptor Inhibits the Activation, Proliferation, and Antibody Production of Human B Cells

The positive coreceptor function of complement receptor type 2 [CR2 (CD21)] on B cells is generally accepted, although its role in the enhancement of antibody production had only been proven in mice. The importance of this phenomenon prompted reinvestigation of the functional consequences of coclustering CD21 and the B cell receptor (BCR) on primary human cells. We found that, at non-stimulatory concentrations of anti-IgG/A/M, coclustering the BCR and CR2 enhanced the Ca²⁺ response, while activation marker expression, cytokine production, proliferation, and antibody production were all inhibited upon the coengagement of CR2 and BCR on human B cells. Thus, the “textbook dogma” claiming that C3d acts as an adjuvant to enhance humoral immunity is relevant only to mice and not to humans.

Complement Receptors and Their Role in Leukocyte Recruitment and Phagocytosis

The complement system is deeply embedded in our physiology and immunity. Complement activation generates a multitude of molecules that converge simultaneously on the opsonization of a target for phagocytosis and activation of the immune system via soluble anaphylatoxins. This response is used to control microorganisms and to remove dead cells, but also plays a major role in stimulating the adaptive immune response and the regeneration of injured tissues. Many of these effects inherently depend on complement receptors expressed on leukocytes and parenchymal cells, which, by recognizing complement-derived molecules, promote leukocyte recruitment, phagocytosis of microorganisms and clearance of immune complexes. Here, the plethora of information on the role of complement receptors will be reviewed, including an analysis of how this functionally and structurally diverse group of molecules acts jointly to exert the full extent of complement regulation of homeostasis.

From Classical to Unconventional: The Immune Receptors Facilitating Platelet Responses to Infection and Inflammation

Platelets have long been recognized for their role in maintaining the balance between hemostasis and thrombosis. While their contributions to blood clotting have been well established, it has been increasingly evident that their roles extend to both innate and adaptive immune functions during infection and inflammation. In this comprehensive review, we describe the various ways in which platelets interact with different microbes and elicit immune responses either directly, or through modulation of leukocyte behaviors.

The pathological role of B cells in systemic lupus erythematosus: From basic research to clinical

Systemic lupus erythematosus (SLE) is an autoimmune disease that often occurs in females of child-bearing age. It involves multiple systems and severely threatens human life. One of the typical characteristics of SLE is the formation of immune complexes with autoantibodies produced by B cells that target various autoantigens, thus indicating the pivotal role of B cells in the pathogenesis of SLE. Increasing evidence has shown abnormal expression of B cells in the peripheral blood of SLE patients. Moreover, numerous studies have shown that B cells in SLE patients are abnormally activated, as well as aberrantly differentiated, and are involved in the inflammatory cytokine milieu, abnormal transcription factor activity, and signalling pathways. Several biological therapies targeting B cells, such as anti-CD20 antibodies, have been intensively studied in preclinical and clinical trials. However, the results have not met expectations. Therefore, new therapies targeting B cells are in great need. This review will summarize the latest progress in basic research on B cells to better understand the pathogenesis of SLE and will discuss the outcomes of B-cell-targeting treatments that provide potential therapeutic targets and strategies for SLE. Studies have clarified high levels of IL-21 in serum from SLE patients and animal models. IL-21 promotes B cell differentiation, which results in antibodies accumulation leads to SLE. Therefore, further studies on IL-21 will give new perspectives on SLE treatments. In addition, the application of drugs targeting plasma cell depletion in SLE patients may also achieve satisfied results in treatment.

Regulation of the complement system and immunological tolerance in pregnancy

Preeclampsia is a serious vascular complication of the human pregnancy, whose etiology is still poorly understood. In preeclampsia, exacerbated apoptosis and fragmentation of the placental tissue occurs due to developmental qualities of the placental trophoblast cells and/or mechanical and oxidative distress to the syncytiotrophoblast, which lines the placental villi. Dysregulation of the complement system is recognized as one of the mechanisms of the disease pathology. Complement has the ability to promote inflammation and facilitate phagocytosis of placenta-derived particles and apoptotic cells by macrophages. In preeclampsia, an overload of placental cell damage or dysregulated complement system may lead to insufficient clearance of apoptotic particles and placenta-derived debris. Excess placental damage may lead to sequestration of microparticles, such as placental vesicles, to capillaries in the glomeruli of the kidney and other vulnerable tissues. This phenomenon could contribute to the manifestations of typical diagnostic symptoms of preeclampsia: proteinuria and new-onset hypertension. In this review we propose that the complement system may serve as a regulator of the complex tolerance and clearance processes that are fundamental in healthy pregnancy. It is therefore recommended that further research be conducted to elucidate the interactions between components of the complement system and immune responses in the context of complicated and healthy pregnancy.

Impaired TLR9 responses in B cells from patients with systemic lupus erythematosus

B cells play a central role in systemic lupus erythematosus (SLE) pathophysiology but dysregulated pathways leading to a break in B cell tolerance remain unclear. Since Toll-like receptor 9 (TLR9) favors the elimination of autoreactive B cells in the periphery, we assessed TLR9 function in SLE by analyzing the responses of B cells and plasmacytoid dendritic cells (pDCs) isolated from healthy donors and patients after stimulation with CpG, a TLR9 agonist. We found that SLE B cells from patients without hydroxychloroquine treatment displayed defective in vitro TLR9 responses, as illustrated by the impaired upregulation of B cell activation molecules and the diminished production of various cytokines including antiinflammatory IL-10. In agreement with CD19 controlling TLR9 responses in B cells, decreased expression of the CD19/CD21 complex on SLE B cells was detected as early as the transitional B cell stage. In contrast, TLR7 function was preserved in SLE B cells, whereas pDCs from SLE patients properly responded to TLR9 stimulation, thereby revealing that impaired TLR9 function in SLE was restricted to B cells. We conclude that abnormal CD19 expression and TLR9 tolerogenic function in SLE B cells may contribute to the break of B cell tolerance in these patients.

Immune Tolerance to Apoptotic Self Is Mediated Primarily by Regulatory B1a Cells

The chronic autoimmune inflammatory diseases, systemic lupus erythematosus and Sjogren's syndrome, develop when tolerance to apoptotic cells (ACs) is lost. We have previously reported that this tolerance is maintained by innate-like, IL-10 secreting regulatory B cells. Two questions remained. First, do these regulatory B cells belong predominantly to a single subset of steady-state B cells and second, what is their specificity? We report here that innate-like B cells with markers characteristic for B1a cells (CD43+veCD19hiCD5+veIgMhiIgDlo) constitute 80% of splenic and 96% of peritoneal B cells that respond to ACs by secreting IL-10. AC responsive B1a cells secrete self-reactive natural antibodies (NAbs) and IL-10, which is augmented by toll-like receptor (TLR) 7 or TLR9 stimulation. In so doing, they both accelerate the clearance of dying cells by macrophages and inhibit their potential to mount proinflammatory immune responses. While B1a cells make prolonged contact with ACs, they do not require TIM1 or complement to mediate their regulatory function. In an animal model of neural inflammation (experimental autoimmune encephalomyelitis), just 105 activated B1a B cells was sufficient to restrain inflammation. Activated B1a B cells also induced antigen-specific T cells to secrete IL-10. Hence, regulatory B1a cells specifically recognize and augment tolerance to apoptotic self via IL-10 and NAbs; but once activated, can also prevent autoimmune mediated inflammation.

Nanovaccine for immunotherapy and reduced hepatitis-B virus in humanized model

Chronic Hepatitis B Virus (HBV) infections are severe with weak antiviral immune responses. The lack of an appropriate small animal model for chronic hepatitis, a major hurdle for studying the immunotolerance and immunopathogenesis induced by hepatitis B viral (HBV) infection. In this study, for enhancing the antibody production efficiency the prepared polymeric HBsAg-loaded nanoparticles (nanovaccine) will be tested in immune-deficit mice, which suffer from chronic Hepatitis B virus. Vaccination of Balb/c mice by this prepared nanoparticles that were engrafted with peripheral blood mononuclear cells (PBMCs), which was already lethally irradiated and transplanted by the bone marrow of NOD (knockout mice) mice. In the present study, after the vaccination detected the high frequencies of immunoglobulin G (IgG)-secreting B cells and mitogen-responsive interferon-Y (IFN-Y) secreting T cells in serum, determined by specific ELISA technique. During the entire observation period, unvaccinated animals showed lower concentration of specific IgG secreting B cells and IFN-Y secreting T cells found in comparison to vaccinated mice group. Chronic HBV carrier PBMCs transplanted into the chimera failed to produce antigen and increased the antibodies production due to vaccination. Furthermore, another advantage was that the viral gene expression and viral DNA replication was no longer observed in vaccinated group. This prepared nanovaccine formulations is better for the cure of Hepatitis B viral infection carrier. Therefore, specific memory responses were elicited by vaccination with Hepatitis B virus surface (HBsAg) antigen of chimeric mice transplanted with PBMCs derived from HBV donors.

5'UTR +24T>C CR2 is not associated with nasopharyngeal carcinoma development in the North Region of Portugal

OBJECTIVE

We have analysed the association of the +24T>C polymorphism (rs3813946) in CR2, the cellular receptor for Epstein-Barr virus (EBV), in the susceptibility for the development of nasopharyngeal carcinoma (NPC).

METHODS

A retrospective case-control study was developed with peripheral blood samples from 111 individuals with NPC and 608 healthy individuals (controls) from the North region of Portugal. The genotyping analysis was performed by allelic discrimination real-time PCR using a TaqMan(®) SNP Genotyping Assay.

RESULTS

The genotype distribution was 62.2% TT, 34.2% TC and 3.6% CC for NPC patients; and 65.0%, 30.6% and 4.4%, respectively, for controls. Our study showed no statistical association between the genotype distribution in controls and all types of NPC (P = 0.717); nevertheless, the analysis showed statistically significant differences (P = 0.038) regarding cases with well- or moderately differentiated types of NPC suggesting that +24CC/CT genotypes are associated with increased risk (OR = 4.16; 95% CI 1.28-15.7; P = 0.016).

CONCLUSIONS

This is the first study in Western populations to characterize the association of the CR2 +24T>C polymorphism in NPC development, and our results suggest that more studies are required to clarify the impact on NPC susceptibility in different populations.

Non-CpG Oligonucleotides Exert Adjuvant Effects by Enhancing Cognate B Cell-T Cell Interactions, Leading to B Cell Activation, Differentiation, and Isotype Switching

Natural and synthetic nucleic acids are known to exert immunomodulatory properties. Notably, nucleic acids are known to modulate immune function via several different pathways and various cell types, necessitating a complex interpretation of their effects. In this study we set out to compare the effects of a CpG motif containing oligodeoxynucleotide (ODN) with those of a control and an inhibitory non-CpG ODN during cognate B cell-T cell interactions. We employed an antigen presentation system using splenocytes from TCR transgenic DO11.10 mice and the ovalbumin peptide recognized by the TCR as model antigen. We followed early activation events by measuring CD69 expression, late activation by MHC class II expression, cell division and antibody production of switched, and nonswitched isotypes. We found that both of the tested non-CpG ODN exerted significant immunomodulatory effects on early T cell and on late B cell activation events. Importantly, a synergism between non-CpG effects and T cell help acting on B cells was observed, resulting in enhanced IgG production following cognate T cell-B cell interactions. We propose that non-CpG ODN may perform as better adjuvants when a strong antigen-independent immune activation, elicited by CpG ODNs, is undesirable.

Syk is indispensable for CpG-induced activation and differentiation of human B cells

B cells are efficiently activated by CpG oligodeoxynucleotides (ODNs) to produce pro-inflammatory cytokines and antibody (Ab). Here, we describe a so far unidentified, spleen tyrosine kinase (Syk)-dependent pathway, which is indispensable for CpG-induced human B cell activation. We show that triggering of B cells by CpG results in Syk and src kinase phosphorylation, proliferation, as well as cytokine and Ab production independent of the BCR. Notably, all these functions are abrogated when Syk is inhibited. We demonstrate that CpG-induced Syk activation originates from the cell surface in a TLR9-dependent manner. While inhibition of Syk does not influence the uptake of CpG ODNs, activation of the kinase is a prerequisite for the delivery of CpG into TLR9-containing endolysosomes and for the CpG-induced up-regulation of TLR9 expression. Our results reveal an alternative, Syk-dependent pathway of CpG-induced B cell stimulation, which is initiated at the plasma membrane and seems to be an upstream requirement for endosomal TLR9-driven B cell proliferation and differentiation.

Association of complement receptor 2 polymorphisms with innate resistance to HIV-1 infection

HIV-1 induces activation of complement through the classical and lectin pathways. However, the virus incorporates several membrane-bound or soluble regulators of complement activation (RCA) that inactivate complement. HIV-1 can also use the complement receptors (CRs) for complement-mediated antibody-dependent enhancement of infection (Ć-ADE). We hypothesize that hypofunctional polymorphisms in RCA or CRs may protect from HIV-1 infection. For this purpose, 139 SNPs located in 19 RCA and CRs genes were genotyped in a population of 201 Spanish HIV-1-exposed seronegative individuals (HESN) and 250 HIV-1-infected patients. Two SNPs were associated with infection susceptibility, rs1567190 in CR2 (odds ratio (OR) = 2.27, P = 1 × 10(-4)) and rs2842704 in C4BPA (OR = 2.11, P = 2 × 10(-4)). To replicate this finding, we analyzed a cohort of Italian, sexually HESN individuals. Although not significant (P = 0.25, OR = 1.57), similar genotypic proportions were obtained for the CR2 marker rs1567190. The results of the two association analyses were combined through a random effect meta-analysis, with a significant P-value of 2.6 x 10(-5) (OR = 2.07). Furthermore, we found that the protective CR2 genotype is correlated with lower levels CR2 mRNA as well as differences in the ratio of the long and short CR2 isoforms.

The complement system in systemic lupus erythematosus: an update

The complement system plays a major role in the autoimmune disease, systemic lupus erythematosus (SLE). However, the role of complement in SLE is complex since it may both prevent and exacerbate the disease. In this review, we explore the latest findings in complement-focused research in SLE. C1q deficiency is the strongest genetic risk factor for SLE, although such deficiency is very rare. Various recently discovered genetic associations include mutations in the complement receptors 2 and 3 as well as complement inhibitors, the latter related to earlier onset of nephritis. Further, autoantibodies are a distinct feature of SLE that are produced as the result of an adaptive immune response and how complement can affect that response is also being reviewed. SLE generates numerous disease manifestations involving contributions from complement such as glomerulonephritis and the increased risk of thrombosis. Furthermore, since most of the complement system is present in plasma, complement is very accessible and may be suitable as biomarker for diagnosis or monitoring of disease activity. This review highlights the many roles of complement for SLE pathogenesis and how research has progressed during recent years.

Genetics and epigenetics of systemic lupus erythematosus

Genetics unquestionably contributes to systemic lupus erythematosus (SLE) predisposition, progression and outcome. Nevertheless, single-gene defects causing lupus-like phenotypes have been infrequently documented. The majority of the identified genetic SLE risk factors are, therefore, common variants, responsible for a small effect on the global risk. Recently, genome wide association studies led to the identification of a growing number of gene variants associated with SLE susceptibility, particular disease phenotypes, and antibody profiles. Further studies addressed the biological effects of these variants. In addition, the role of epigenetics has recently been revealed. These combined efforts contributed to a better understanding of SLE pathogenesis and to the characterization of clinically relevant pathways. In this review, we describe SLE-associated single-gene defects, common variants, and epigenetic changes. We also discuss the limitations of current methods and the challenges that we still have to face in order to incorporate genomic and epigenomic data into clinical practice.

Coadministration of antigen-conjugated and free CpG: effects of in vitro and in vivo interactions in a murine model

CpG oligodeoxynucleotides (CpG) are widely studied as promising adjuvants in vaccines against a range of diseases including infection, cancer or allergy. Conjugating antigen to CpG has been shown to potentiate the adjuvant effect via enhancing antigen uptake and danger signaling by the very same cell. In the present study, using biotinylated CpG and streptavidin as a model system, we demonstrate that CpG motif containing free and antigen-conjugated oligonucleotides do not compete in terms of cell activation via TLR9, but do compete for cellular uptake. Antigen-conjugated CpG enhances cellular association and uptake of the antigen by antigen-presenting cells (APC) and T cells. Free CpG efficiently competes with antigen-CpG conjugates in BMDC and T cells, but shows weak or no competition in B cells that have higher TLR9 expression. Vaccination with antigen-conjugated CpG or with a mixture of antigen and CpG elevates the level of antigen-specific antibodies but co-administration of CpG-antigen conjugates and free CpG adversely effects immunogenicity. These observations may help optimize CpG-based vaccine formulation.

TLR9 is dispensable for intestinal ischemia/reperfusion-induced tissue damage

The mortality rate due to intestinal ischemia/reperfusion (IR) remains at 60-80%. As toll-like receptor (TLR) 4 has been shown to be critical for IR injury in several organs, including the intestine, and TLR9 is necessary for IR-induced damage of the liver, we investigated the hypothesis that TLR9 is involved in intestinal IR-induced damage. Wildtype (C57Bl/6) and TLR9(-/-) mice were subjected to intestinal IR or Sham treatment. Several markers of damage and inflammation were assessed, including mucosal injury, eicosanoid production, cytokine secretion and complement deposition. Although IR-induced injury was not altered, PGE(2) production was decreased in TLR9(-/-) mice. Attenuated PGE(2) production was not due to differences in percentage of lipids or COX-2 transcription. The data indicate that TLR9 is not required for IR-induced injury or inflammation of the intestine.