A critical role of natural immunoglobulin M in immediate defense against systemic bacterial infection

A secondary metabolite of Limosilactobacillusreuteri R2lc drives strain-specific pathology in a spontaneous mouse model of multiple sclerosis

Limosilactobacillus reuteri is an immunomodulatory bacterium enriched in non-industrialized microbiomes, making it a therapeutic candidate for chronic diseases. However, effects of L. reuteri strains in mouse models of multiple sclerosis have been contradictory. Here, we show that treatment of spontaneous relapsing-remitting experimental autoimmune encephalomyelitis (EAE) mice with L. reuteri R2lc, a strain that activates the aryl hydrocarbon receptor (AhR) through the pks gene cluster, resulted in severe pathology. In contrast, a pks mutant and a pks-negative strain (PB-W1) failed to exacerbate EAE and exhibited reduced pathology compared to R2lc despite earlier disease onset in PB-W1 mice. Differences in pathology occurred in parallel with a pks-dependent downregulation of AhR-related genes, reduced occludin expression in the forebrain, and altered concentrations of immune cells. This work establishes a molecular foundation for strain-specific effects on autoimmunity, which has implications for our understanding of how microbes contribute to chronic conditions and the selection of microbial therapeutics.

Secreted IgM deficiency alters the retinal landscape enhancing neurodegeneration associated with aging

BACKGROUND

Maintenance of the retina, part of the central nervous system, and other structures in the eye is critical for vision preservation. Aging increases the prevalence of vision impairment, including glaucoma, macular degeneration, and diabetic retinopathy. The retina is primarily maintained by glial cells; however, recent literature suggests that lymphocytes may play a role in the homeostasis of central nervous system tissues. Natural antibodies are produced by B cells without infection or immunization and maintain tissue homeostasis. Here, we explored the potential role of natural immunoglobulin M (IgM) produced by B lymphocytes in maintaining retinal health during aging in mice.

RESULTS

Our results indicate that the vitreous humor of both mice and humans contains IgM and IgG, suggesting that these immunoglobulins may play a role in ocular function. Furthermore, we observed that aged mice lacking secreted IgM (µs-/-) exhibited pronounced retinal degeneration, accompanied by reactive gliosis, and a proinflammatory cytokine environment. This contrasts with the aged wild-type counterparts, which retain their ability to secrete IgM and maintain a better retinal structure and anti-inflammatory environment. In addition to these findings, the absence of secreted IgM was associated with significant alterations in the retinal pigment epithelium, including disruptions to its morphology and signs of increased stress. This was further observed in changes to the blood-retinal-barrier, which is critical for regulation of retinal homeostasis.

CONCLUSIONS

These data suggest a previously unrecognized association between a lack of secreted IgM and alterations in the retinal microenvironment, leading to enhanced retinal degeneration during aging. Although the precise mechanism remains unclear, these findings highlight the potential importance of secreted IgM in processes that support retinal health over time. By increasing our understanding of ocular aging, these results show that there is a broader role for the immune system in retinal function and integrity in advanced age, opening new areas for the exploration of immune-related interventions in age-associated retinal conditions.

Persistent splenic-derived IgMs preferentially recognize factor VIII A2 and C2 domain epitopes but do not alter antibody production

BACKGROUND

The most significant treatment complication for patients with hemophilia A is the development of neutralizing immunoglobins (Igs) G, termed inhibitors, against factor VIII (FVIII), which prevent FVIII replacement therapy. Low titers of FVIII-specific IgMs have been identified in hemophilia A patients with and without inhibitors, as well as in healthy individuals. However, the duration and influence of IgMs on the immune response to FVIII remains unclear.

OBJECTIVES

To characterize the binding interactions of persistently secreted FVIII-specific IgMs in hemophilia A mice and assess their effect on IgG antibody development.

METHODS

Splenic-derived monoclonal antibodies (mAbs) from immunized FVIII knockout mice were isolated and purified using hybridoma technology. Binding interactions were assessed utilizing a novel fluid-phase enzyme-linked immunosorbent assay and computational modeling with High Ambiguity-Driven protein-protein DOCKing to account for weak IgM binding.

RESULTS

Sixteen porcine cross-reactive and noninhibitory FVIII-specific IgM mAbs were identified. RNA sequencing of FVIII-specific IgMs revealed 13 unique variable, diversity, and joining (VDJ)/variable and joining (VJ) sequences indicating derivation from 13 unique B cell clones. The IgMs demonstrated polyclonal and polyreactive binding to FVIII in vitro and in silico. Molecular docking studies with reconstructed IgM variable, diversity, and joining/variable and joining regions identified frequent IgM interactions with amino acid residues K376, T381, K437, R2215, or K2249 within the FVIII A2 and C2 domains. Injections of individual IgMs prior to FVIII exposure and co-injection of FVIII/IgM immune complexes did not affect de novo FVIII antibody production.

CONCLUSION

Persistent FVIII-specific IgMs are polyclonal but preferentially bind the A2 and C2 domains. FVIII/IgM immune complex formation does not significantly alter inhibitor development.

Functions of IgM fc receptor (FcµR) related to autoimmunity

Unlike Fc receptors for switched immunoglobulin (Ig) isotypes, Fc receptor for IgM (FcµR) is selectively expressed by lymphocytes. The ablation of the FcµR gene in mice impairs B cell tolerance as evidenced by concomitant production of autoantibodies of IgM and IgG isotypes. In this essay, we reiterate the autoimmune phenotypes observed in mutant mice, ie IgM homeostasis, dysregulated humoral immune responses including autoantibodies, and Mott cell formation. We also propose the potential phenotypes in individuals with FCMR deficiency and the model for FcµR-mediated regulation of self-reactive B cells.

A B cell screen against endogenous retroviruses identifies glycan-reactive IgM that recognizes a broad array of enveloped viruses

Endogenous retroviruses (ERVs), comprising a substantial portion of the vertebrate genome, are remnants of ancient genetic invaders. ERVs with near-intact coding potential reactivate in B cell-deficient mice. To study how B cells contribute to host anti-ERV immunity, we used an antigen-baiting strategy to enrich B cells reactive to ERV surface antigens. We identified ERV-reactive B-1 cells expressing germline-encoded natural IgM antibodies in naïve mice, the level of which further increases upon innate immune sensor stimulation. B cell receptor repertoire profiling of ERV-reactive B-1 cells revealed increased usage of the Igh VH gene that gives rise to glycan-specific antibodies targeting terminal N-acetylglucosamine moieties on ERV glycoproteins, which further engage the complement pathway to mediate anti-ERV responses. These same antibodies also recognize glycoproteins of other enveloped viruses but not self-proteins. These results reveal an innate antiviral mechanism of germline-encoded antibodies with broad reactivity to enveloped viruses, which constitutes a natural antibody repertoire capable of preventing the emergence of infectious ERVs.

Increased expression of ABO blood group antigens secretion phenotype with O blood group and age advances

OBJECTIVES

To ascertain the prevalence of ABH antigen secretors and non-secretors among Yemenis. In addition to explore the factors that may affect the expression of the secretion phenotype.

METHODS

This cross-sectional study was carried out between May and September 2022 on 215 healthy Yemeni individuals at the International Malaysian University, Ibb, Yemen. The participants were tested for blood group antigen on their blood samples using standard test tube method using the suitable ABH antisera. Saliva was collected and tested for secretion using hemagglutination inhibition test with suitable A, B, and H antisera. Before collecting the blood samples, informed consent was obtained from each participant and complete data and history questionnaire were collected by the research team.

RESULTS

In general, 78.1% of Yemini participants were found to be secretor (80% men and 73.3% females). This percentage increased within O blood group (95%) and decreased within AB blood group (54%) individuals. Both O and AB blood groups showed statistically significant association with secretor trait. Also, it was noticed that age advance increases the expression of Se gene. In addition, the secretor state increased among Rh-negative people.

CONCLUSION

The frequency of ABH secretors was 78.1% among Ibb province population in Yemen. Blood group O revealed the greatest frequency (95%), whereas blood group AB showed the lowest secretor frequency (54%). The secretor phenotype was highly expressed gradually with advance age then decline.

Theories of immune recognition: Is anybody right?

The clonal selection theory (CST) is the centrepiece of the current paradigm used to explain immune recognition and memory. Throughout the past decades, the original CST had been expanded and modified to explain new experimental evidences since its original publication by Burnet. This gave origin to new paradigms that govern experimental immunology nowadays, such as the associative recognition of antigen model and the stranger/danger signal model. However, these new theories also do not fully explain experimental findings such as natural autoimmune immunoglobulins, idiotypic networks, low and high dose tolerance, and dual-receptor T and B cells. To make sense of these empirical data, some authors have been trying to change the paradigm of immune cognition using a systemic approach, analogies with brain processing and concepts from second-order cybernetics. In the present paper, we review the CST and some of the theories/hypotheses derived from it, focusing on immune recognition. We point out their main weaknesses and highlight arguments made by their opponents and believers. We conclude that, until now, none of the proposed theories can fully explain the totality of immune phenomena and that a theory of everything is needed in immunology.

The common variable immunodeficiency IgM repertoire narrowly recognizes erythrocyte and platelet glycans

BACKGROUND

Autoimmune cytopenias (AICs) regularly occur in profoundly IgG-deficient patients with common variable immunodeficiency (CVID). The isotypes, antigenic targets, and origin(s) of their disease-causing autoantibodies are unclear.

OBJECTIVE

We sought to determine reactivity, clonality, and provenance of AIC-associated IgM autoantibodies in patients with CVID.

METHODS

We used glycan arrays, patient erythrocytes, and platelets to determine targets of CVID IgM autoantibodies. Glycan-binding profiles were used to identify autoreactive clones across B-cell subsets, specifically circulating marginal zone (MZ) B cells, for sorting and IGH sequencing. The locations, transcriptomes, and responses of tonsillar MZ B cells to different TH- cell subsets were determined by confocal microscopy, RNA-sequencing, and cocultures, respectively.

RESULTS

Autoreactive IgM coated erythrocytes and platelets from many CVID patients with AICs (CVID+AIC). On glycan arrays, CVID+AIC plasma IgM narrowly recognized erythrocytic i antigens and platelet i-related antigens and failed to bind hundreds of pathogen- and tumor-associated carbohydrates. Polyclonal i antigen-recognizing B-cell receptors were highly enriched among CVID+AIC circulating MZ B cells. Within tonsillar tissues, MZ B cells secreted copious IgM when activated by the combination of IL-10 and IL-21 or when cultured with IL-10/IL-21-secreting FOXP3-CD25hi T follicular helper (Tfh) cells. In lymph nodes from immunocompetent controls, MZ B cells, plentiful FOXP3+ regulatory T cells, and rare FOXP3-CD25+ cells that represented likely CD25hi Tfh cells all localized outside of germinal centers. In CVID+AIC lymph nodes, cellular positions were similar but CD25hi Tfh cells greatly outnumbered regulatory cells.

CONCLUSIONS

Our findings indicate that glycan-reactive IgM autoantibodies produced outside of germinal centers may contribute to the autoimmune pathogenesis of CVID.

Mechanical control of antigen detection and discrimination by T and B cell receptors

The adaptive immune response is orchestrated by just two cell types, T cells and B cells. Both cells possess the remarkable ability to recognize virtually any antigen through their respective antigen receptors-the T cell receptor (TCR) and B cell receptor (BCR). Despite extensive investigations into the biochemical signaling events triggered by antigen recognition in these cells, our ability to predict or control the outcome of T and B cell activation remains elusive. This challenge is compounded by the sensitivity of T and B cells to the biophysical properties of antigens and the cells presenting them-a phenomenon we are just beginning to understand. Recent insights underscore the central role of mechanical forces in this process, governing the conformation, signaling activity, and spatial organization of TCRs and BCRs within the cell membrane, ultimately eliciting distinct cellular responses. Traditionally, T cells and B cells have been studied independently, with researchers working in parallel to decipher the mechanisms of activation. While these investigations have unveiled many overlaps in how these cell types sense and respond to antigens, notable differences exist. To fully grasp their biology and harness it for therapeutic purposes, these distinctions must be considered. This review compares and contrasts the TCR and BCR, placing emphasis on the role of mechanical force in regulating the activity of both receptors to shape cellular and humoral adaptive immune responses.

Siraitia grosvenorii Extract Protects Lipopolysaccharide-Induced Intestinal Inflammation in Mice via Promoting M2 Macrophage Polarization

Siraitia grosvenorii has anti-inflammatory, antioxidant, and immune-regulating effects, while macrophages play an important role in reducing inflammation. However, it is still unclear whether Siraitia grosvenorii extract (SGE) is effective in reducing inflammation by regulating macrophages. This study investigated the regulatory effect of SGE on macrophage polarization in a lipopolysaccharide (LPS)-induced intestinal inflammation model after establishing the model in vitro and in vivo. The results from the in vivo model showed that, compared with the LPS group, SGE significantly improved ileal morphology, restored the ileal mucosal barrier, and reduced intestinal and systemic inflammation by increasing CD206 and reducing iNOS proteins. In the in vitro model, compared with the LPS group, SGE significantly reduced the expression of iNOS protein and cytokines (TNF-α, IL-1β, and IFN-γ) while significantly increasing the protein expression of CD206 in RAW264.7 cells. In conclusion, SGE can alleviate intestinal inflammation, protect the mucus barrier, and block the systemic immunosuppressive response by increasing M2 macrophages.

Natural antibodies drive type 2 immunity in response to damage-associated molecular patterns

Allergic airway disease (AAD) is an example of type 2 inflammation that leads to chronic airway eosinophilia controlled by CD4 Th2 cells. Inflammation is reinforced by mast cells and basophils armed with allergen-specific IgE made by allergen-specific B2 B cells of the adaptive immune system. Little is known about how AAD is affected by innate B1 cells, which produce natural antibodies (NAbs) that facilitate apoptotic cell clearance and detect damage- and pathogen-associated molecular patterns (DAMPS and PAMPS). We used transgenic mice lacking either B cells or NAbs in distinct mouse models of AAD that require either DAMPS or PAMPS as the initial trigger for type 2 immunity. In a DAMP-induced allergic model, driven by alum and uric acid, mouse strains lacking B cells (CD19DTA), NAbs (IgHEL MD4), or all secreted antibodies (sIgm-/-Aid-/-) displayed a significant reduction in both eosinophilia and Th2 priming compared with WT or Aid-/- mice lacking only germinal center-dependent high-affinity class-switched antibodies. Replenishing B cell-deficient mice with either unimmunized B1 B cells or NAbs during sensitization restored eosinophilia, suggesting that NAbs are required for licensing antigen-presenting cells to prime type 2 immunity. Conversely, PAMP-dependent type 2 priming to house dust mite or Aspergillus was not dependent on NAbs. This study reveals an underappreciated role of B1 B cell-generated NAbs in selectively driving DAMP-induced type 2 immunity.

Exploring the multifaceted role of RASGRP1 in disease: immune, neural, metabolic, and oncogenic perspectives

RAS guanyl releasing protein 1 (RASGRP1) is a guanine nucleotide exchange factor (GEF) characterized by the presence of a RAS superfamily GEF domain. It functions as a diacylglycerol (DAG)-regulated nucleotide exchange factor, specifically activating RAS through the exchange of bound GDP for GTP. Activation of RAS by RASGRP1 has a wide range of downstream effects at the cellular level. Thus, it is not surprising that many diseases are associated with RASGRP1 disorders. Here, we present an overview of the structure and function of RASGRP1, its crucial role in the development, expression, and regulation of immune cells, and its involvement in various signaling pathways. This review comprehensively explores the relationship between RASGRP1 and various diseases, elucidates the underlying molecular mechanisms of RASGRP1 in each disease, and identifies potential therapeutic targets. This study provides novel insights into the role of RASGRP1 in insulin secretion and highlights its potential as a therapeutic target for diabetes. The limitations and challenges associated with studying RASGRP1 in disease are also discussed.

Gut microbiota and serum metabolome reveal the mechanism by which TCM polysaccharides alleviate salpingitis in laying hens challenged by bacteria

This paper aimed to evaluate the effect of 3 kinds of TCM polysaccharides instead of antibiotics in preventing salpingitis in laying hens. After feeding the laying hens with Lotus leaf polysaccharide, Poria polysaccharide, and Epimedium polysaccharide, mixed bacteria (E. coli and Staphylococcus aureus) were used to infect the oviduct to establish an inflammation model. Changes in antioxidant, serum immunity, anti-inflammatory, gut microbiota, and serum metabolites were evaluated. The results showed that the 3 TCM polysaccharides could increase the expression of antioxidant markers SOD, GSH, and CAT, and reduce the accumulation of MDA in the liver; the contents of IgA and IgM in serum were increased. Decreased the mRNA expression of TLR4, NFκB, TNF-α, IFN-γ, IL1β, IL6, and IL8, and increased the mRNA expression of anti-inflammatory factor IL5 in oviduct tissue. 16sRNA high-throughput sequencing revealed that the 3 TCM polysaccharides improved the intestinal flora disturbance caused by bacterial infection, increased the abundance of beneficial bacteria such as Bacteroides and Actinobacillus, and decreased the abundance of harmful bacteria such as Romboutsia, Turicibacter, and Streptococcus. Metabolomics showed that the 3 TCM polysaccharides could increase the content of metabolites such as 3-hydroxybutyric acid and isobutyl-L-carnitine, and these results could alleviate the further development of salpingitis. In conclusion, the present study has found that using TCM polysaccharides instead of antibiotics was a feasible way to prevent bacterial salpingitis in laying hens, which might make preventing this disease no longer an issue for breeding laying hens.

Correlation of ABO Blood Group Susceptibility to Disease Severity of SARS-COV-2: An Original Research

COVID-19, the Ecumenical Pandemic that hit Wuhan, Hubei Province, China, in 2019 has instigated an emergency situation all over the globe. Current scientific corroborations highlighted the role of zoonotic cross-over species transmission for the spread of the deadly virus SARSCoV2. The proposition of ABO blood grouping to susceptibility for various infectious diseases has been documented in the past since blood group antigens constitute polymorphic traits that are inherited among humans, therefore are frequent targets in epidemiological studies.

Aim

To correlate the ABO blood group susceptibility to disease severity in COVID-19-positive cases among Indian populations.

Objectives

Association of ABO blood group patterns to disease severity in COVID-19-positive cases.

Materials and Methods

A cross-sectional, observational study design was conducted among 700 confirmed COVID-19-positive cases admitted to the tertiary health care center in Maharashtra, India. The data collected were subjected to statistical analysis.

Results

Blood group 'A' positive was frequent (40%) in severe COVID-19 (E group) disease, and 'O' positive blood group was frequent in moderate COVID-19 disease (34.62%).

Conclusion

ABO Blood grouping can be used as one of the efficient biomarker for COVID-19, thereby providing a new platform for therapeutic applications in the field of research.

Destabilisation of T cell-dependent humoral immunity in sepsis

Sepsis is a heterogeneous condition defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. For some, sepsis presents as a predominantly suppressive disorder, whilst others experience a pro-inflammatory condition which can culminate in a 'cytokine storm'. Frequently, patients experience signs of concurrent hyper-inflammation and immunosuppression, underpinning the difficulty in directing effective treatment. Although intensive care unit mortality rates have improved in recent years, one-third of discharged patients die within the following year. Half of post-sepsis deaths are due to exacerbation of pre-existing conditions, whilst half are due to complications arising from a deteriorated immune system. It has been suggested that the intense and dysregulated response to infection may induce irreversible metabolic reprogramming in immune cells. As a critical arm of immune protection in vertebrates, alterations to the adaptive immune system can have devastating repercussions. Indeed, a marked depletion of lymphocytes is observed in sepsis, correlating with increased rates of mortality. Such sepsis-induced lymphopenia has profound consequences on how T cells respond to infection but equally on the humoral immune response that is both elicited by B cells and supported by distinct CD4+ T follicular helper (TFH) cell subsets. The immunosuppressive state is further exacerbated by functional impairments to the remaining lymphocyte population, including the presence of cells expressing dysfunctional or exhausted phenotypes. This review will specifically focus on how sepsis destabilises the adaptive immune system, with a closer examination on how B cells and CD4+ TFH cells are affected by sepsis and the corresponding impact on humoral immunity.

Small Intestinal Goblet Cells Control Humoral Immune Responses and Mobilization During Enteric Infection

Humoral immune responses within the gut play diverse roles including pathogen clearance during enteric infections, maintaining tolerance, and facilitating the assemblage and stability of the gut microbiota. How these humoral immune responses are initiated and contribute to these processes are well studied. However, the signals promoting the expansion of these responses and their rapid mobilization to the gut mucosa are less well understood. Intestinal goblet cells form goblet cell-associated antigen passages (GAPs) to deliver luminal antigens to the underlying immune system and facilitate tolerance. GAPs are rapidly inhibited during enteric infection to prevent inflammatory responses to innocuous luminal antigens. Here we interrogate GAP inhibition as a key physiological response required for effective humoral immunity. Independent of infection, GAP inhibition resulted in enrichment of transcripts representing B cell recruitment, expansion, and differentiation into plasma cells in the small intestine (SI), which were confirmed by flow cytometry and ELISpot assays. Further we observed an expansion of isolated lymphoid follicles within the SI, as well as expansion of plasma cells in the bone marrow upon GAP inhibition. S1PR1-induced blockade of leukocyte trafficking during GAP inhibition resulted in a blunting of SI plasma cell expansion, suggesting that mobilization of plasma cells from the bone marrow contributes to their expansion in the gut. However, luminal IgA secretion was only observed in the presence of S. typhimurium infection, suggesting that although GAP inhibition mobilizes a mucosal humoral immune response, a second signal is required for full effector function. Overriding GAP inhibition during enteric infection abrogated the expansion of laminar propria IgA+ plasma cells. We conclude that GAP inhibition is a required physiological response for efficiently mobilizing mucosal humoral immunity in response to enteric infection.

Secreted IgM modulates IL-10 expression in B cells

IL-10+ B cells are critical for immune homeostasis and restraining immune responses in infection, cancer, and inflammation; however, the signals that govern IL-10+ B cell differentiation are ill-defined. Here we find that IL-10+ B cells expand in mice lacking secreted IgM ((s)IgM-/-) up to 10-fold relative to wildtype (WT) among all major B cell and regulatory B cell subsets. The IL-10+ B cell increase is polyclonal and presents within 24 hours of birth. In WT mice, sIgM is produced prenatally and limits the expansion of IL-10+ B cells. Lack of the high affinity receptor for sIgM, FcμR, in B cells translates into an intermediate IL-10+ B cell phenotype relative to WT or sIgM-/- mice. Our study thus shows that sIgM regulates IL-10 programming in B cells in part via B cell-expressed FcμR, thereby revealing a function of sIgM in regulating immune homeostasis.

Polyreactivity of antibodies from different B-cell subpopulations is determined by distinct sequence patterns of variable region

An antibody molecule that can bind to multiple distinct antigens is defined as polyreactive. In the present study, we performed statistical analyses to assess sequence correlates of polyreactivity of >600 antibodies cloned from different B-cell types of healthy humans. The data revealed several sequence patterns of variable regions of heavy and light immunoglobulin chains that determine polyreactivity. The most prominent identified patterns were increased number of basic amino acid residues, reduced frequency of acidic residues, increased number of aromatic and hydrophobic residues, and longer length of CDR L1. Importantly, our study revealed that antibodies isolated from different B-cell populations used distinct sequence patterns (or combinations of them) for polyreactive antigen binding. Furthermore, we combined the data from sequence analyses with molecular modeling of selected polyreactive antibodies and demonstrated that human antibodies can use multiple pathways for achieving antigen-binding promiscuity. These data reconcile some contradictions in the literature regarding the determinants of antibody polyreactivity. Moreover, our study demonstrates that the mechanism of polyreactivity of antibodies evolves during immune response and might be tailored to specific functional properties of different B-cell compartments. Finally, these data can be of use for efforts in the development and engineering of therapeutic antibodies.

Multifaceted Tissue-Protective Functions of Polyvalent Immunoglobulin Preparations in Severe Infections-Interactions with Neutrophils, Complement, and Coagulation Pathways

Severe infections induce immune defense mechanisms and initial tissue damage, which produce an inflammatory neutrophil response. Upon dysregulation of these responses, inflammation, further tissue damage, and systemic spread of the pathogen may occur. Subsequent vascular inflammation and activation of coagulation processes may cause microvascular obstruction at sites distal to the primary site of infection. Low immunoglobulin (Ig) M and IgG levels have been detected in patients with severe infections like sCAP and sepsis, associated with increased severity and mortality. Based on Ig's modes of action, supplementation with polyvalent intravenous Ig preparations (standard IVIg or IgM/IgA-enriched Ig preparations) has long been discussed as a treatment option for severe infections. A prerequisite seems to be the timely administration of Ig preparations before excessive tissue damage has occurred and coagulopathy has developed. This review focuses on nonclinical and clinical studies that evaluated tissue-protective activities resulting from interactions of Igs with neutrophils, complement, and the coagulation system. The data indicate that coagulopathy, organ failure, and even death of patients can possibly be prevented by the timely combined interactions of (natural) IgM, IgA, and IgG with neutrophils and complement.

The Effects of Mammary Gland ATIII Overexpression on the General Health of Dairy Goats and Their Anti-Inflammatory Response to LPS Stimulation

Antithrombin III is an important anticoagulant factor with anti-inflammatory properties. However, few studies have explored its anti-inflammatory actions in ATIII overexpressed transgenic animals. In this study, the dairy goats with mammary overexpression of ATIII were used to investigate their general health, milk quality and particularly their response to inflammatory challenge. The results showed that transgenic goats have a normal phenotype regarding their physiological and biochemical parameters, including whole blood cells, serum protein levels, total cholesterol, urea nitrogen, uric acid, and total bilirubin, compared to the WT. In addition, the quality of milk also improved in transgenic animals compared to the WT, as indicated by the increased milk fat and dry matter content and the reduced somatic cell numbers. Under the stimulation of an LPS injection, the transgenic goats had elevated contents of IGA, IGM and superoxide dismutase SOD, and had reduced proinflammatory cytokine release, including IL-6, TNF-α and IFN-β. A 16S rDNA sequencing analysis also showed that the transgenic animals had a similar compositions of gut microbiota to the WT goats under the stimulation of LPS injections. Mammary gland ATIII overexpression in dairy goats is a safe process, and it did not jeopardize the general health of the transgenic animals; moreover, the compositions of their gut microbiota also improved with the milk quality. The LPS stimulation study suggests that the increased ATIII expression may directly or indirectly suppress the inflammatory response to increase the resistance of transgenic animals to pathogen invasion. This will be explored in future studies.

The Role of Inflammation in Cholestatic Liver Injury

Cholestasis is a common clinical event in which bile formation and excretion are blocked, leading to retention of bile acids or bile salts; whether it occurs intra- or extrahepatically, primary or secondary, its pathogenesis is still unclear and is influenced by a combination of factors. In a variety of inflammatory and immune cells such as neutrophils, macrophages (intrahepatic macrophages are also known as Kupffer cells), mast cells, NK cells, and even T cells in humoral immunity and B cells in cellular immunity, inflammation can be a "second strike" against cholestatic liver injury. These cells, stimulated by a variety of factors such as bile acids, inflammatory chemokines, and complement, can be activated and accumulate in the cholestatic liver, and with the involvement of inflammatory mediators and modulation by cytokines, can lead to destruction of hepatocytes and bile duct epithelial cells and exacerbate (and occasionally retard) the progression of cholestatic liver disease. In this paper, we summarized the new research advances proposed so far regarding the relationship between inflammation and cholestasis, aiming to provide reference for researchers and clinicians in the field of cholestatic liver injury research.

A DNA vaccine (EG95-PT1/2/3-IL2) encoding multi-epitope antigen and IL-2 provokes efficient and long-term immunity to echinococcosis

Echinococcosis is a highly prevalent global zoonosis, and vaccines are required. The commercial vaccine based on a protein-based subunit (EG95), however, is limited by its insufficient cellular immunity, a short protection period, and limited prevention against novel mutant strains. Herein, we applied bioinformatics to develop a DNA vaccine (pEG95-IL2) expressing both multi-epitope-based antigens (EG95-PT1/2/3) and an IL-2 adjuvant to regulate T cell differentiation and memory cell response. EG95-PT1/2/3 was screened with hierarchical structure prediction from the epitope conformation of B cells with high confidence across various species to guarantee immunogenicity. Importantly, cationic arginine-rich lipid nanoparticles (RNP) were utilized as a delivery vehicle to form lipoplexes that had a transfection efficiency of nearly two orders of magnitude greater than that of commercial reagents (Lipofectamine 2000 and polyethyleneimine) with both immune and nonimmune cells (DC2.4 and L929 cells, respectively). RNP/pEG95-IL2 lipoplexes displayed a robust and long-term antigen expression, as well as adjuvant effects during the immunization. Consequently, intramuscular injection of RNP/pEG95-IL2 elicited similar humoral immune responses and significantly greater cellular responses in mice when compared with those of the commercial vaccine. In addition, the inoculation protocol of RNP/pEG95-IL2 with sequential booster further strengthens cellular immunity in comparison with the homologous booster. Those findings provide a promising strategy for improving plasmid vaccine efficacy.

Natural Antibodies Mediate Protection Against Acinetobacter baumannii Respiratory Infections

BACKGROUND

Acinetobacter baumannii causes a wide range of dangerous infections due to the emergence of pandrug-resistant strains. Therefore, there is a need for alternative therapeutics to treat these infections, including those targeting the host immune responses. However, immune responses, especially the humoral response against this pathogen, are poorly understood.

METHODS

This study investigated the lymphocyte-mediated innate immune resistance to A. baumannii AB5075 pulmonary infection using B- and T-cell-deficient (Rag2-/-) mice, the protective effect of natural antibodies (NAbs), and the expression of complement-mediated responses using a mouse pneumonia model.

RESULTS

Our results showed that intranasally infected Rag2-/- mice are impaired in clearing bacteria from lung, liver, and spleen at 24 hours postinfection compared to wildtype mice. Animal pretreatment with normal mouse serum or purified antibodies from naive mice rescued Rag2-/- mice from infection. Analysis of C3 complement protein binding demonstrated that NAbs increased C3 protein deposition on A. baumannii cells, indicating the activation of the classical complement pathway by NAbs.

CONCLUSIONS

Overall, our study shows that NAbs mediate innate immune resistance against A. baumannii, a finding that may lead to the development of effective therapies against human infections caused by this antibiotic-resistant A. baumannii.

Age-related changes in antigen-specific natural antibodies are influenced by sex

Introduction

Natural antibody (NAb) derived from CD5+ B-1 cells maintains tissue homeostasis, controls inflammation, aids in establishing long-term protective responses against pathogens, and provides immediate protection from infection. CD5+ B-1 cell NAbs recognize evolutionarily fixed epitopes, such as phosphatidylcholine (PtC), found on bacteria and senescent red blood cells. Anti-PtC antibodies are essential in protection against bacterial sepsis. CD5+ B-1 cell-derived NAbs have a unique germline-like structure that lacks N-additions, a feature critical for providing protection against infection. Previously, we demonstrated the repertoire and germline status of PtC+CD5+ B-1 cell IgM obtained from male mice changes with age depending on the anatomical location of the B-1 cells. More recently, we demonstrated serum antibody from aged female mice maintains protection against pneumococcal infection, whereas serum antibody from male mice does not provide protection.

Results

Here, we show that aged female mice have significantly more splenic PtC+CD5+ B-1 cells and more PtC specific serum IgM than aged male mice. Furthermore, we find both age and biological sex related repertoire differences when comparing B cell receptor (BCR) sequencing results of PtC+CD5+ B-1 cells. While BCR germline status of PtC+CD5+ B-1 cells from aged male and female mice is similar in the peritoneal cavity, it differs significantly in the spleen, where aged females retain germline configuration and aged males do not. Nucleic acid sensing toll-like receptors are critical in the maintenance of PtC+ B-1 cells; therefore, to begin to understand the mechanism of differences observed between the male and female PtC+CD5+ B-1 cell repertoire, we analyzed levels of cell-free nucleic acids and found increases in aged females.

Conclusion

Our results suggest the antigenic milieu differs between aged males and females, leading to differential selection of antigen-specific B-1 cells over time. Further elucidation of how biological sex differences influence the maintenance of B-1 cells within the aging environment will be essential to understand sex and age-related disparities in the susceptibility to bacterial infection and will aid in the development of more effective vaccination and/or therapeutic strategies specific for males and females.

TLR7 and IgM: Dangerous Partners in Autoimmunity

The B cell antigen receptor (BCR)-repertoire is capable of recognizing a nearly unlimited number of antigens. Inevitably, the random nature of antibody gene segment rearrangement, needed in order to provide mature B cells, will generate autoreactive specificities. Once tolerance mechanisms fail to block the activation and differentiation of autoreactive B cells, harmful autoantibodies may get secreted establishing autoimmune diseases. Besides the hallmark of autoimmunity, namely IgG autoantibodies, IgM autoantibodies are also found in many autoimmune diseases. In addition to pathogenic functions of secreted IgM the IgM-BCR expressing B cell might be the initial check-point where, in conjunction with innate receptor signals, B cell mediated autoimmunity starts it fateful course. Recently, pentameric IgM autoantibodies have been shown to contribute significantly to the pathogenesis of various autoimmune diseases, such as rheumatoid arthritis (RA), autoimmune hemolytic anemia (AIHA), pemphigus or autoimmune neuropathy. Further, recent studies suggest differences in the recognition of autoantigen by IgG and IgM autoantibodies, or propose a central role of anti-ACE2-IgM autoantibodies in severe COVID-19. However, exact mechanisms still remain to be uncovered in detail. This article focuses on summarizing recent findings regarding the importance of autoreactive IgM in establishing autoimmune diseases.

The Impacts of Transdermal Application of Corticosterone on Toad (Rhinella icterica) Immunity

Recent studies have shown that acute physiological increases in endogenous glucocorticoid levels have immunostimulatory effects. Although post-acute stress immunosuppressive effects have also been described, the difference between enhancing and suppressing the immune response seems mediated by the stressor's duration, intensity, and the immune component under analysis. To elicit physiologically relevant corticosterone levels that can be found in Rhinella icterica toads after stressful events (e.g., restraint or captivity) and understand how acute increased glucocorticoid levels of different intensities affect corticosterone and testosterone plasma levels and immune parameters (in vitro plasma bacterial killing ability, neutrophil-to-lymphocyte ratio, and in vivo phagocytosis of peritoneal leukocytes), we submitted toads to the transdermal application of two corticosterone doses (1 and 10 μg). Corticosterone transdermal application increased corticosterone plasma levels with different intensities: 3 times for 1 μg and fourteen times for 10 μg, compared to the vehicle, and the neutrophil-to-lymphocyte ratio increased regardless of the corticosterone dose. However, there was no effect on testosterone levels and bacterial killing ability. Interestingly, both corticosterone doses promoted immunosuppression, decreasing peritoneal leukocytes' phagocytosis activity by 60% for toads receiving the dose of 1µg and 40% for those receiving 10 μg. Our results show the complexity of the relationship between increased corticosterone levels and immunomodulation. The different corticosterone doses promoted increases of distinct magnitudes in corticosterone plasma levels, with the less intense increase in corticosterone levels generating greater cell-mediated immunosuppression. Future studies using different corticosterone doses to achieve and compare physiological vs. pharmacological hormone levels are imperative to understanding these interrelationships between corticosterone and immune response.

Cryomicroscopy reveals the structural basis for a flexible hinge motion in the immunoglobulin M pentamer

Immunoglobulin M (IgM) is the most ancient of the five isotypes of immunoglobulin (Ig) molecules and serves as the first line of defence against pathogens. Here, we use cryo-EM to image the structure of the human full-length IgM pentamer, revealing antigen binding domains flexibly attached to the asymmetric and rigid core formed by the Cμ4 and Cμ3 constant regions and the J-chain. A hinge is located at the Cμ3/Cμ2 domain interface, allowing Fabs and Cμ2 to pivot as a unit both in-plane and out-of-plane. This motion is different from that observed in IgG and IgA, where the two Fab arms are able to swing independently. A biased orientation of one pair of Fab arms results from asymmetry in the constant domain (Cμ3) at the IgM subunit interacting most extensively with the J-chain. This may influence the multi-valent binding to surface-associated antigens and complement pathway activation. By comparison, the structure of the Fc fragment in the IgM monomer is similar to that of the pentamer, but is more dynamic in the Cμ4 domain.

CD6 deficiency impairs early immune response to bacterial sepsis

CD6 is a lymphocyte-specific scavenger receptor expressed on adaptive (T) and innate (B1a, NK) immune cells, which is involved in both fine-tuning of lymphocyte activation/differentiation and recognition of bacterial-associated molecular patterns (i.e., lipopolysaccharide). However, evidence on CD6’s role in the physiological response to bacterial infection was missing. Our results show that induction of monobacterial and polymicrobial sepsis in Cd6^−/− mice results in lower survival rates and increased bacterial loads and pro-inflammatory cytokine levels. Steady state analyses of Cd6^−/− mice show decreased levels of natural polyreactive antibodies, concomitant with decreased cell counts of spleen B1a and marginal zone B cells. Adoptive transfer of wild-type B cells and mouse serum, as well as a polyreactive monoclonal antibody improve Cd6^−/− mouse survival rates post-sepsis. These findings support a nonredundant role for CD6 in the early response against bacterial infection, through homeostatic expansion and functionality of innate-related immune cells.

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CD6 is a nonredundant receptor in early immune response to sepsis

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Cd6−/− mice show higher susceptibility to bacterial sepsis

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Cd6−/− mice show lower B1a and MZB cell and natural polyreactive antibody levels

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B cell and serum transfer restore susceptibility of Cd6−/− mice to bacterial sepsis

Natural Antibodies Alert the Adaptive Immune System of the Presence of Transformed Cells in Early Tumorigenesis

Recent studies have revealed a critical role for natural Abs (NAbs) in antitumor immune responses. However, the role of NAbs in cancer immunosurveillance remains unexplored, mainly because of the lack of in vivo models that mimic the early recognition and elimination of transforming cells. In this article, we propose a role for NAbs in alerting the immune system against precancerous neoantigen-expressing cells immediately after they escape intrinsic tumor suppression mechanisms. We identify four distinct reproducible, trackable, MHC-matched neoantigen-expressing cell models that do not form tumors as the end point. This amplified readout in the critical window prior to tumor formation allows investigation of new mediators of cancer immunosurveillance. We found that neoantigen-expressing cells adoptively transferred in NAb-deficient mice persisted, whereas they were eliminated in wild-type mice, indicating that the circulating NAb repertoire alerts the immune system to the presence of transformed cells. Moreover, immunity is mounted against immunogenic and nonimmunogenic neoantigens contained in the NAb-tagged cells, regardless of whether the NAb directly recognizes the neoantigens. Beyond these neoantigen-expressing model systems, we observed a significantly greater tumor burden in chemically and virally induced tumor models in NAb-deficient mice compared with wild-type mice. Restoration of the NAb repertoire in NAb-deficient mice elicited the recognition and elimination of neoantigen-expressing cells and cancer. These data show that NAbs are required and sufficient for elimination of transformed cells early in tumorigenesis. These models can now be used to investigate how NAbs stimulate immunity via recognition receptors to eliminate precancerous cells.

Protective role of host complement system in Aspergillus fumigatus infection

Invasive aspergillosis (IA) is a life-threatening fungal infection for immunocompromised hosts. It is, therefore, necessary to understand the immune pathways that control this infection. Although the primary infection site is the lungs, aspergillosis can disseminate to other organs through unknown mechanisms. Herein we have examined the in vivo role of various complement pathways as well as the complement receptors C3aR and C5aR1 during experimental systemic infection by Aspergillus fumigatus, the main species responsible for IA. We show that C3 knockout (C3^-/-) mice are highly susceptible to systemic infection of A. fumigatus. Intriguingly, C4^-/- and factor B (FB)^-/- mice showed susceptibility similar to the wild-type mice, suggesting that either the complement pathways display functional redundancy during infection (i.e., one pathway compensates for the loss of the other), or complement is activated non-canonically by A. fumigatus protease. Our in vitro study substantiates the presence of C3 and C5 cleaving proteases in A. fumigatus. Examination of the importance of the terminal complement pathway employing C5^-/- and C5aR1^-/- mice reveals that it plays a vital role in the conidial clearance. This, in part, is due to the increased conidial uptake by phagocytes. Together, our data suggest that the complement deficiency enhances the susceptibility to systemic infection by A. fumigatus.

Pla2g2a promotes innate Th2-type immunity lymphocytes to increase B1a cells

Newborns require early generation of effective innate immunity as a primary physiological mechanism for survival. The neonatal Lin28⁺Let7^– developmental pathway allows increased generation of Th2-type cells and B1a (B-1 B) cells compared to adult cells and long-term maintenance of these initially generated innate cells. For initial B1a cell growth from the neonatal to adult stage, Th2-type IL-5 production from ILC2s and NKT2 cells is important to increase B1a cells. The Th17 increase is dependent on extracellular bacteria, and increased bacteria leads to lower Th2-type generation. Secreted group IIA-phospholipase A2 (sPLA2-IIA) from the Pla2g2a gene can bind to gram-positive bacteria and degrade bacterial membranes, controlling microbiota in the intestine. BALB/c mice are Pla2g2a⁺, and express high numbers of Th2-type cells and B1a cells. C57BL/6 mice are Pla2g2a-deficient and distinct from the SLAM family, and exhibit fewer NKT2 cells and fewer B1a cells from the neonatal to adult stage. We found that loss of Pla2g2a in the BALB/c background decreased IL-5 from Th2-type ILC2s and NKT2s but increased bacterial-reactive NKT17 cells and MAIT cells, and decreased the number of early-generated B1a cells and MZ B cells and the CD4/CD8 T cell ratio. Low IL-5 by decreased Th2-type cells in Pla2g2a loss led to low early-generated B1a cell growth from the neonatal to adult stage. In anti-thymocyte/Thy-1 autoreactive μκ transgenic (ATAμκ Tg) Pla2g2a⁺ BALB/c background C.B17 mice generated NKT2 cells that continuously control CD1d⁺ B1 B cells through old aging and lost CD1d in B1 B cells generating strong B1 ATA B cell leukemia/lymphoma. Pla2g2a-deficient ATAμκTg C57BL/6 mice suppressed the initial B1a cell increase, with low/negative spontaneous leukemia/lymphoma generation. These data confirmed that the presence of Pla2g2a to control bacteria is important to allow the neonatal to adult stage. Pla2g2a promotes innate Th2-type immunity lymphocytes to increase early generated B1a cells.

Lipopolysaccharide-Induced Immunological Tolerance in Monocyte-Derived Dendritic Cells

Bacterial lipopolysaccharides (LPS), also referred to as endotoxins, are major outer surface membrane components present on almost all Gram-negative bacteria and are major determinants of sepsis-related clinical complications including septic shock. LPS acts as a strong stimulator of innate or natural immunity in a wide variety of eukaryotic species ranging from insects to humans including specific effects on the adaptive immune system. However, following immune stimulation, lipopolysaccharide can induce tolerance which is an essential immune-homeostatic response that prevents overactivation of the inflammatory response. The tolerance induced by LPS is a state of reduced immune responsiveness due to persistent and repeated challenges, resulting in decreased expression of pro-inflammatory modulators and up-regulation of antimicrobials and other mediators that promote a reduction of inflammation. The presence of environmental-derived LPS may play a key role in decreasing autoimmune diseases and gut tolerance to the plethora of ingested antigens. The use of LPS may be an important immune adjuvant as demonstrated by the promotion of IDO1 increase when present in the fusion protein complex of CTB-INS (a chimera of the cholera toxin B subunit linked to proinsulin) that inhibits human monocyte-derived DC (moDC) activation, which may act through an IDO1-dependent pathway. The resultant state of DC tolerance can be further enhanced by the presence of residual E. coli lipopolysaccharide (LPS) which is almost always present in partially purified CTB-INS preparations. The approach to using an adjuvant with an autoantigen in immunotherapy promises effective treatment for devastating tissue-specific autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes (T1D).

Evidence underscoring immunological and clinical pathological changes associated with Sarcoptes scabiei infection: synthesis and meta-analysis

BACKGROUND

Sarcoptes scabiei is one of the most impactful mammalian parasites. There has been much research on immunological and clinical pathological changes associated with S. scabiei parasitism across a range of host species. This rich body of literature is complex, and we seek to bring that complexity together in this study. We first (1) synthesise narrative reviews of immunopathological relationships to S. scabiei infection to construct overarching hypotheses; then (2) undertake a systematic meta-analysis of primary literature on immunological and clinical pathological changes; and lastly (3) contrast our findings from the meta-analysis to our synthesis from narrative reviews.

METHODS

We synthesised 55 narrative reviews into two overarching hypotheses representing type I and type IV immune responses to S. scabiei infection. We then systematically extracted all literature reporting immunological variables, acute phase proteins, oxidant/antioxidant status, and erythrocytic, hepatological and nephrological changes, calculating 565 effect sizes between controls and sarcoptic mange affected groupings, refining (simplifying) hypotheses from narrative reviews.

RESULTS

Immunological and clinical pathological parameters were most often studied in dogs (n = 12) and humans (n = 14). Combining immunological and clinical pathological information across mammalian species (n = 19) helped yield general insights into observed disease responses. This is evidenced by interspecific consensus in 27 immunological and clinical pathology variables (6/26 type I hypersensitivity, 3/20 type IV hypersensitivity, 6/10 oxidant/antioxidant status, 3/6 acute phase protein, 4/7 erythrocytic, and 5/10 hepatological/nephrological).

CONCLUSIONS

Elevated IgE, eosinophils and mast cells in type I hypersensitivity response corresponded to what was described in narrative reviews. Results from type IV hypersensitivity response suggested typical antibody response, however cell-mediated response was less evident. Some consensus of acute phase protein response and shifted oxidant/antioxidant balance and slight evidence of anemia. We highlight the need for mange/scabies studies to more routinely compare immunological and clinical pathological changes against controls, and include collection of a more standardised suite of variables among studies.

B-1b Cells Have Unique Functional Traits Compared to B-1a Cells at Homeostasis and in Aged Hyperlipidemic Mice With Atherosclerosis

Immunoglobulin M (IgM) to oxidation specific epitopes (OSE) are inversely associated with atherosclerosis in mice and humans. The B-1b subtype of B-1 cells secrete IgM to OSE, and unlike B-1a cells, are capable of long-lasting IgM memory. What attributes make B-1b cells different than B-1a cells is unknown. Our objectives were to determine how B-1b cells produce more IgM compared to B-1a cells at homeostatic condition and to see the differences in the B-1a and B-1b cell distribution and IgM CDR-H3 sequences in mice with advanced atherosclerosis. Here, in-vivo studies demonstrated greater migration to spleen, splenic production of IgM and plasma IgM levels in ApoE^-/-Rag1^-/- mice intraperitoneally injected with equal numbers of B-1b compared to B-1a cells. Bulk RNA seq analysis and flow cytometry of B-1a and B-1b cells identified CCR6 as a chemokine receptor more highly expressed on B-1b cells compared to B-1a. Knockout of CCR6 resulted in reduced B-1b cell migration to the spleen. Moreover, B-1b cell numbers were significantly higher in spleen of aged atherosclerotic ApoE^-/- mice compared to young ApoE^-/- mice. Single cell sequencing results of IgHM in B-1a and B-1b cells from peritoneal cavity and spleen of atherosclerotic aged ApoE^-/- mice revealed significantly more N additions at the V-D and D-J junctions, greater diversity in V region usage and CDR-H3 sequences in B-1b compared to B-1a cells. In summary, B-1b cells demonstrated enhanced CCR6-mediated splenic migration, IgM production, and IgM repertoire diversification compared to B-1a cells. These findings suggest that potential strategies to selectively augment B-1b cell numbers and splenic trafficking could lead to increased and more diverse IgM targeting OSE to limit atherosclerosis.

Bruton's Tyrosine Kinase Deficiency Ameliorates Antimicrobial Host Defense during Peritonitis Induced by Pathogenic Escherichia coli

Peritonitis and abdominal sepsis remain major health problems and challenge for clinicians. Bruton's tyrosine kinase (Btk) is a versatile signaling protein involved in the regulation of B cell development and function, as well as innate host defense. In the current study, we aimed to explore the role of Btk in the host response during peritonitis and sepsis in mice induced by a gradually growing pathogenic strain of Escherichia coli bacteria. We found that Btk deficiency ameliorated antibacterial host defense during the late stage of E. coli-induced peritonitis. Btk was not required for cytokine and chemokine release in response to either E. coli or lipopolysaccharide and did not impact organ damage evoked by E. coli. Btk deficiency also did not alter neutrophil influx to the primary site of infection. However, the absence of Btk modestly enhanced phagocytosis of E. coli by neutrophils. These results indicate that Btk-mediated signaling is superfluous for inflammatory responses and remarkably detrimental for antibacterial defense during E. coli-induced peritonitis.

Leveraging Antibody, B Cell and Fc Receptor Interactions to Understand Heterogeneous Immune Responses in Tuberculosis

Despite over a century of research, Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), continues to kill 1.5 million people annually. Though less than 10% of infected individuals develop active disease, the specific host immune responses that lead to Mtb transmission and death, as well as those that are protective, are not yet fully defined. Recent immune correlative studies demonstrate that the spectrum of infection and disease is more heterogenous than has been classically defined. Moreover, emerging translational and animal model data attribute a diverse immune repertoire to TB outcomes. Thus, protective and detrimental immune responses to Mtb likely encompass a framework that is broader than T helper type 1 (Th1) immunity. Antibodies, Fc receptor interactions and B cells are underexplored host responses to Mtb. Poised at the interface of initial bacterial host interactions and in granulomatous lesions, antibodies and Fc receptors expressed on macrophages, neutrophils, dendritic cells, natural killer cells, T and B cells have the potential to influence local and systemic adaptive immune responses. Broadening the paradigm of protective immunity will offer new paths to improve diagnostics and vaccines to reduce the morbidity and mortality of TB.

Postnatal regulation of B-1a cell development and survival by the CIC-PER2-BHLHE41 axis

B-1 cell development mainly occurs via fetal and neonatal hematopoiesis and is suppressed in adult bone marrow hematopoiesis. However, little is known about the factors inhibiting B-1 cell development at the adult stage. We report that capicua (CIC) suppresses postnatal B-1a cell development and survival. CIC levels are high in B-1a cells and gradually increase in transitional B-1a (TrB-1a) cells with age. B-cell-specific Cic-null mice exhibit expansion of the B-1a cell population and a gradual increase in TrB-1a cell frequency with age but attenuated B-2 cell development. CIC deficiency enhances B cell receptor (BCR) signaling in transitional B cells and B-1a cell viability. Mechanistically, CIC-deficiency-mediated Per2 derepression upregulates Bhlhe41 levels by inhibiting CRY-mediated transcriptional repression for Bhlhe41, consequently promoting B-1a cell formation in Cic-null mice. Taken together, CIC is a key transcription factor that limits the B-1a cell population at the adult stage and balances B-1 versus B-2 cell formation.

GPR183 Is Dispensable for B1 Cell Accumulation and Function, but Affects B2 Cell Abundance, in the Omentum and Peritoneal Cavity

B1 cells constitute a specialized subset of B cells, best characterized in mice, which is abundant in body cavities, including the peritoneal cavity. Through natural and antigen-induced antibody production, B1 cells participate in the early defense against bacteria. The G protein-coupled receptor 183 (GPR183), also known as Epstein-Barr virus-induced gene 2 (EBI2), is an oxysterol-activated chemotactic receptor that regulates migration of B cells. We investigated the role of GPR183 in B1 cells in the peritoneal cavity and omentum. B1 cells expressed GPR183 at the mRNA level and migrated towards the GPR183 ligand 7α,25-dihydroxycholesterol (7α,25-OHC). GPR183 knock-out (KO) mice had smaller omenta, but with normal numbers of B1 cells, whereas they had fewer B2 cells in the omentum and peritoneal cavity than wildtype (WT) mice. GPR183 was not responsible for B1 cell accumulation in the omentum in response to i.p. lipopolysaccharide (LPS)-injection, in spite of a massive increase in 7α,25-OHC levels. Lack of GPR183 also did not affect B1a- or B1b cell-specific antibody responses after vaccination. In conclusion, we found that GPR183 is non-essential for the accumulation and function of B1 cells in the omentum and peritoneal cavity, but that it influences the abundance of B2 cells in these compartments.

Seroprevalence of IgG and IgM antibodies to Haemophilus influenzae type a in Canadian children

BACKGROUND

Over the last 2 decades, Haemophilus influenzae type a (Hia) has emerged as a significant cause of invasive disease in some geographic regions and populations. Recognition of the importance of Hia in the etiology of serious disease, particularly in young children, prompted the development of a new protein-capsular polysaccharide conjugate vaccine, similar in design to a vaccine against H. influenzae type b. At present, understanding of Hia immunology is incomplete; the immunological correlate of protection against invasive disease is unknown.

METHODS

Our objective was to study Hia antibody in children of various ages residing in a Canadian province with low incidence rates of invasive disease. The enzyme-linked immunosorbent assays were performed to quantify plasma IgG and IgM specific to Hia capsular polysaccharide in 133 children (3 months to 16 years).

RESULTS

Both anti-Hia IgG and IgM concentrations increased with age and were significantly higher in older children; a positive correlation between age and concentrations of Hia antibody was found. IgM antibody concentrations were significantly higher than IgG, with mean IgM concentrations over 10 times larger than IgG across all age groups.

CONCLUSIONS

The steady rise of naturally acquired, Hia-specific IgG and IgM concentrations in a pediatric population with low incidence rates of invasive Hia disease suggests the exposure to some cross-reactive environmental antigens as a major source of the antibody. However, the carriage rates of Hia in the region are unknown and further seroepidemiological studies are warranted. Although natural antibody may protect certain population groups against invasive disease, immunization of younger children will be essential to prevent serious infections if Hia continues to spread across North America.

Unique B-1 cells specific for both N-pyrrolated proteins and DNA evolve with apolipoprotein E deficiency

Lysine N-pyrrolation, a posttranslational modification, which converts lysine residues to N^ε-pyrrole-L-lysine, imparts electronegative properties to proteins, causing them to mimic DNA. Apolipoprotein E (apoE) has been identified as a soluble receptor for pyrrolated proteins (pyrP), and accelerated lysine N-pyrrolation has been observed in apoE-deficient (apoE^−/−) hyperlipidemic mice. However, the impact of pyrP accumulation consequent to apoE deficiency on the innate immune response remains unclear. Here, we investigated B-1a cells known to produce germline-encoded immunoglobulin M (IgM) from mice deficient in apoE and identified a particular cell population that specifically produces IgM antibodies against pyrP and DNA. We demonstrated an expansion of B-1a cells involved in IgM production in the peritoneal cavity of apoE^−/− mice compared with wild-type mice, consistent with a progressive increase of IgM response in the mouse sera. We found that pyrP exhibited preferential binding to B-1a cells and facilitated the production of IgM. B cell receptor analysis of pyrP-specific B-1a cells showed restricted usage of gene segments selected from the germline gene set; most sequences contained high levels of non-templated-nucleotide additions (N-additions) that could contribute to junctional diversity of B cell receptors. Finally, we report that a subset of monoclonal IgM antibodies against pyrP/DNA established from the apoE^−/− mice also contained abundant N-additions. These results suggest that the accumulation of pyrP due to apoE deficiency may influence clonal diversity in the pyrP-specific B cell repertoire. The discovery of these unique B-1a cells for pyrP/DNA provides a key link connecting covalent protein modification, lipoprotein metabolism, and innate immunity.

Adaptive tolerance: Protection through self-recognition

The random nature of immunoglobulin gene segment rearrangement inevitably leads to the generation of self-reactive B cells. Avoidance of destructive autoimmune reactions is necessary in order to maintain physiological homeostasis. However, current central and peripheral tolerance concepts fail to explain the massive number of autoantibody-borne autoimmune diseases. Moreover, recent studies have shown that in physiological mouse models autoreactive B cells were neither clonally deleted nor kept in an anergic state, but were instead able to mount autoantibody responses. We propose that activation of autoreactive B cells is induced by polyvalent autoantigen complexes that can occur under physiological conditions. Repeated encounter of autoantigen complexes leads to the production of affinity-matured autoreactive IgM that protects its respective self-targets from degradation. We refer to this novel mechanism as adaptive tolerance. This article discusses the discovery of adaptive tolerance and the unexpected role of high affinity IgM autoantibodies.

Development of T-cell engagers selective for cells co-expressing two antigens

T cell-engaging bispecific antibodies (TCEs) are clinically effective treatments for hematological cancers. While the utility of TCEs in solid malignancies is being explored, toxicities arising from antigen expression on normal tissues have slowed or halted several clinical trials. Here, we describe the development of TCEs that preferentially drive T cell-mediated death against target cells co-expressing two tumor-associated antigens. We show that Ly6E and B7-H4 are simultaneously expressed on approximately 50% of breast cancers, whereas normal tissue expression is limited and mostly orthogonal. Traditional bispecific TCEs targeting a singular antigen, either Ly6E or B7-H4, are active when paired with high-affinity CD3-engagers, but normal tissue expression presents a toxicity risk. Treatment with a murine cross-reactive B7-H4-TCE results in rapid and severe weight loss in mice along with damage to B7-H4-expressing tissues. To overcome on-target toxicity, we designed trispecific antibodies co-targeting Ly6E, B7-H4, and CD3 and characterized the impact of dual-antigen binding and the relative placement of each binding domain on tumor killing in vitro and in vivo. In vitro killing of tumor cells co-expressing both antigens correlates to the placement of the higher affinity B7-H4 binding domain, with only modest enhancements seen upon addition of Ly6E binding. In xenograft models, avid binding of appropriately designed trispecific TCEs enables tumor growth inhibition while evading the poor tolerability seen with active bispecific TCEs. Collectively these data highlight the potential for dual-antigen targeting to improve safety and efficacy, and expand the scope of tumors that may effectively be treated by TCEs.

Abbreviations: Chimeric antigen receptor T cells (CAR-Ts), dual-antigen targeted T cell engagers (DAT-TCE), Fragment antigen-binding (Fab), Hematoxylin and eosin (H&E), Institutional Animal Care and Use Committee (IACUC), Immunoglobulin G (IgG), immunohistochemistry (IHC), NOD SCID gamma (NSG), peripheral blood mononuclear cells (PBMCs), surface plasmon resonance (SPR), T cell-engagers (TCEs)

Remarkable positive effects of figwort (Scrophularia striata) on improving growth performance, and immunohematological parameters of fish

This study was conducted to investigate the effect of figwort on the growth and immunohematological parameters of common carp (14.20 ± 0.53 g). Four experimental diets were developed to feed fish for eight weeks: control, Figw10 (10 g/kg figwort), Figw20 (20 g/kg figwort), and Figw30 (30 g/kg figwort). The results showed that fish fed dietary Figw10 gained more weight (38.25 g) than control (P < 0.05). Regarding immunohematological parameters, fish fed dietary Figw30 had a higher level of white blood cells (31.2 10³/mm³), hematocrit (35.82%), blood performance (14.63), total protein (1.96 g/dL), albumin (0.79 g/dL), globulin (1.17 g/dL), lymphocyte (70.53%), monocyte (3.03%), alternative hemolytic complement activity (ACH50) (147.76 u/mL), lysozyme (62.19 u/mL), and bactericidal activities (135.24) than the control group (P < 0.05). After 14 days of the challenge with Aeromonas hydrophila, the Figw30 treatment had the highest survival ratio (61.76%) compared to the control with 26.46%. Further, after the challenge, fish fed dietary Figw30 had a higher value of immunoglobulin M (42.00 μg/mL), antibody titer (19.23), complement component 3 (296.39 μg/mL), and complement component 4 (97.91 μg/mL) when compared with those fed control diet (P < 0.05). In conclusion, the optimum dosage for providing the best immune response was 30 g/kg in diet.

A Comparison Between 1 Day versus 7 Days of Sepsis in Mice with the Experiments on LPS-Activated Macrophages Support the Use of Intravenous Immunoglobulin for Sepsis Attenuation

Background

Because survival and death after sepsis are partly due to a proper immune adaptation and immune dysregulation, respectively, survivors and moribund mice after cecal ligation and puncture (CLP) sepsis surgery and in vitro macrophage experiments were explored.

Methods

Characteristics of mice at 1-day and 7-days post-CLP, the representative of moribund mice (an innate immune hyper-responsiveness) and survivors (a successful control on innate immunity), respectively. In parallel, soluble heat aggregated immunoglobulin (sHA-Ig), a representative of immune complex, was tested in lipopolysaccharide (LPS)-activated macrophages together with a test of intravenous immunoglobulin (IVIG), a molecule of adaptive immunity, on CLP sepsis mice.

Results

Except for a slight increase in alanine transaminase (liver injury), IL-10, endotoxemia, and gut leakage (FITC-dextran assay), most of the parameters in survivors (7-days post-CLP) were normalized, with enhanced adaptive immunity, including serum immunoglobulin (using serum protein electrophoresis) and activated immune cells in spleens (flow cytometry analysis). The addition of sHA-Ig in LPS-activated macrophages reduced supernatant cytokines, cell energy (extracellular flux analysis), reactive oxygen species (ROS), several cell activities (proteomic analysis), and Fc gamma receptors (FcgRs) expression. The loss of anti-inflammatory effect of sHA-Ig in LPS-activated macrophages from mice with a deficiency on Fc gamma receptor IIb (FcgRIIb-/-), the only inhibitory signaling of FcgRs family, when compared with wild-type macrophages, implying the FcgRIIb-dependent mechanism. Moreover, IVIG attenuated sepsis severity in CLP mice as evaluated by serum creatinine, liver enzyme (alanine transaminase), serum cytokines, spleen apoptosis, and abundance of dendritic cells in the spleen (24-h post-CLP) and survival analysis.

Conclusion

Immunoglobulin attenuated LPS-activated macrophages, partly, through the reduced cell energy of macrophages and might play a role in sepsis immune hyper-responsiveness. Despite the debate over IVIG’s use in sepsis, IVIG might be beneficial in sepsis with certain conditions.

Plasma IgM Levels Differentiate between Survivors and Non-Survivors of Culture-Positive and Culture-Negative Sepsis and SIRS: A Pilot Study

Immunoglobulin IgM is important for controlling viral and bacterial infections, and low immunoglobulin levels have been found in sepsis. There is a clear need to stratify sepsis patients according to the presence of an invading organism, compared to no organism identified, and SIRS patients, where organ dysfunction is a result of a non-infective process. The aim of this pilot study in a small cohort of patients with sepsis was to evaluate the association between IgM plasma levels and survival in 47 patients with sepsis and 11 patients diagnosed with organ failure without the identification of a pathogen (SIRS). Patients were admitted to the intensive care unit (ICU) at The Royal Glamorgan Hospital, Llantrisant, UK between 2010 and 2014. We found that low IgM levels were associated with sepsis, but not SIRS. IgM levels did not differ significantly for culture-positive (CP) compared with culture-negative (CN, no organism found) sepsis samples. Kaplan–Meier analysis was used to compare survival curves according to IgM levels, with no significant difference. We observed significantly higher survival in the CP samples when comparing with CN. Cut-off value for IgM (266 μg/mL) for diagnosis of sepsis patients was determined using receiver operator characteristic (ROC) curves with 70% sensitivity, 69% specificity and 92% negative predictive values (NPV), respectively. The corresponding area under the curve (AUC) for the discrimination of sepsis patients was AUC = 0.73, and in a subgroup analysis of CP was AUC = 0.77 and for CN was AUC = 0.79. We confirm IgM as a good diagnostic marker of sepsis. These findings indicate a difference in the pathology between culture-positive versus negative sepsis, SIRS and survival. This indicates that IgM is likely relevant to pathology, because of its role in the early immune response against pathogens, the potentially protective role of natural IgM antibodies, and supports its application in immunoglobulin therapy.

Contribution of classical complement activation and IgM to the control of Rickettsia infection

Pathogenic Rickettsia are obligate intracellular bacteria and the etiologic agents of many life‐threatening infectious diseases. Due to the serious nature of these infections, it is imperative to both identify the responsive immune sensory pathways and understand the associated immune mechanisms that restrict Rickettsia proliferation. Previous studies have demonstrated that the mammalian complement system is both activated during Rickettsia infection and contributes to the immune response to infection. To further define this component of the mammalian anti‐Rickettsia immune response, we sought to identify the mechanism(s) of complement activation during Rickettsia infection. We have employed a series of in vitro and in vivo models of infection to investigate the role of the classical complement activation pathway during Rickettsia infection. Depletion or elimination of complement activity demonstrates that both C1q and pre‐existing IgM contribute to complement activation; thus implicating the classical complement system in Rickettsia‐mediated complement activation. Elimination of the classical complement pathway from mice increases susceptibility to R. australis infection with both increased bacterial loads in multiple tissues and decreased immune activation markers. This study highlights the role of the classical complement pathway in immunity against Rickettsia and implicates resident Rickettsia‐responsive IgM in the response to infection.

Immunological perspectives on spatial and temporal vaccine delivery

The so-called rational design of vaccines has been a very attractive concept and also an important direction for vaccine research and development. However, the underlying rationales, especially on the immunological aspect, remain less systemically and deeply understood. Given the critical role of lymph nodes (LNs) in the induction of B and T cell responses upon vaccination, LN targeting has been a popular strategy in vaccine design. The LN is a highly organized structure; induction of adaptive immune response is highly orchestrated by various types of LN stromal cells and hematopoietic immune cells both spatially and temporally. Thus, not only LN targeting, but also cellular targeting and even subcellular compartment targeting should be considered for specifically enhanced vaccine efficacy. Moreover, temporal control of vaccine antigen and adjuvant delivery may also optimize the immune response.

Evaluation of the nontreponemal IgM antibodies in syphilis serofast patients: A new serologic marker for active syphilis

BACKGROUND

Serofast status is challenging to interpret in clinical work, and distinguishing active syphilis in serofast patients can provide a reference for clinical diagnosis and treatment. However, effective serologic markers for active syphilis are still lacking.

OBJECTIVES

We aimed to explore the possibility of nontreponemal IgM antibodies in distinguishing active syphilis in serofast patients.

METHODS

A total of 1501 clinical serum samples were collected from 301 serofast patients, and nontreponemal IgM antibodies were detected by chemiluminescence immunoassay.

RESULTS

The results showed that a total of 29 samples (9.63%) of 301 serofast patients were positive for nontreponemal IgM antibodies, and our limited follow-up data showed that 66.67% (2/3) of the serofast patients progressed to neurosyphilis and cardiovascular syphilis.

CONCLUSION

These findings demonstrate that most serofast patients with positive nontreponemal IgM antibodies have evidence of progressive syphilis, and nontreponemal IgM antibodies can be used as a new serologic marker for the activity of syphilis. Nontreponemal IgM antibodies may play a role in the management of serofast patients.

Renal Outcome of IgM Nephropathy: A Comparative Prospective Cohort Study

Immunoglobulin M nephropathy (IgMN) is an idiopathic glomerulonephritis characterized by diffuse deposits of IgM in the glomerular mesangium. However, its renal prognosis remains unknown. We compared renal outcomes of IgMN patients with those of patients with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), or mesangial proliferative glomerulonephritis (MsPGN) from a prospective observational cohort, with 1791 patients undergoing native kidney biopsy in eight hospitals affiliated with The Catholic University of Korea between December 2014 and October 2020. IgMN had more mesangial proliferation and matrix expansion than MsPGN and more tubular atrophy and interstitial fibrosis than MCD. IgMN patients had decreased eGFR than MCD patients in the earlier follow-up. However, there was no significant difference in urine protein or eGFR among all patients at the last follow-up. When IgMN was divided into three subtypes, patients with FSGS-like IgMN tended to have lower eGFR than those with MCD-like or MsPGN-like IgMN but higher proteinuria than MsPGN-like IgMN without showing a significant difference. The presence of hypertension at the time of kidney biopsy predicted ≥20% decline of eGFR over two years in IgMN patients. Our data indicate that IgMN would have a clinical course and renal prognosis similar to MCD, FSGS, and MsPGN.