Suppression of Long-Lived Humoral Immunity Following Borrelia burgdorferi Infection

Single-cell transcriptome analysis of the early immune response in the lymph nodes of Borrelia burgdorferi-infected mice

Lyme borreliosis is a disease caused by Borrelia burgdorferi sensu lato bacteria. Borrelia burgdorferi is known to induce prolonged extrafollicular immune responses and abnormal germinal centre formation. The infection fails to generate a neutralizing type of immunity, eventually establishing a persistent infection. Here, we performed single-cell RNA sequencing to characterize the immune landscape of lymph node lymphocytes during the early Borrelia burgdorferi infection in a murine model. Our results indicate key features of an extrafollicular immune response four days after Borrelia burgdorferi infection, including notable B cell proliferation, immunoglobulin class switching to IgG3 and IgG2b isotypes, plasmablast differentiation, and the presence of extrafollicular B cells identified through immunohistochemistry. Additionally, we found infection-derived upregulation of suppressor of cytokine signalling genes Socs1 and Socs3, along with downregulation of genes associated with MHC II antigen presentation in B cells. Our results support the central role of B cells in the immune response of a Borrelia burgdorferi infection, and provide cues of mechanisms behind the determination between extrafollicular and germinal centre responses during Borrelia burgdorferi infection.

Bridging the gap: Insights in the immunopathology of Lyme borreliosis

Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato (Bbsl) genospecies transmitted by Ixodes spp. ticks, is a significant public health concern in the Northern Hemisphere. This review highlights the complex interplay between Bbsl infection and host-immune responses, impacting clinical manifestations and long-term immunity. Early localized disease is characterized by erythema migrans (EM), driven by T-helper 1 (Th1) responses and proinflammatory cytokines. Dissemination to the heart and CNS can lead to Lyme carditis and neuroborreliosis respectively, orchestrated by immune cell infiltration and chemokine dysregulation. More chronic manifestations, including acrodermatitis chronica atrophicans and Lyme arthritis, involve prolonged inflammation as well as the development of autoimmunity. In addition, dysregulated immune responses impair long-term immunity, with compromised B-cell memory and antibody responses. Experimental models and clinical studies underscore the role of Th1/Th2 balance, B-cell dysfunction, and autoimmunity in LB pathogenesis. Moreover, LB-associated autoimmunity parallels mechanisms observed in other infectious and autoimmune diseases. Understanding immune dysregulation in LB provides insights into disease heterogeneity and could provide new strategies for diagnosis and treatment.

Development, Optimization, and Validation of a Quantitative PCR Assay for Borrelia burgdorferi Detection in Tick, Wildlife, and Human Samples

Tick-borne pathogens are growing in importance for human and veterinary research worldwide. We developed, optimized, and validated a reliable quantitative PCR (qPCR; real-time PCR) assay to assess Borrelia burgdorferi infection by targeting two B. burgdorferi genes, ospA and flaB. When assessing previously tested tick samples, its performance surpassed the nested PCR in efficiency, sensitivity, and specificity. Since the detection of Borrelia is more difficult in mammalian samples, the qPCR assay was also assessed using wildlife tissues. For wildlife samples, the sensitivity and specificity of ospA primers, with the incorporation of a pre-amplification step, was equivalent or superior to the nested PCR. For human samples, no primer set was successful with human tissue without culture, but we detected Borrelia with ospA and flaB primers in 50% of the Lyme culture samples, corresponding to 60% of the participants with a Lyme disease diagnosis or suspicion. The specificity of amplification was confirmed by Sanger sequencing. The healthy participant culture samples were negative. This PCR-based direct detection assay performs well for the detection of Borrelia in different biological samples. Advancements in detection methods lead to a better surveillance of Borrelia in vectors and hosts, and, ultimately, enhance human and animal health.

Antibody-mediated immunological memory correlates with long-term Lyme veterinary vaccine protection in mice

Lyme disease, caused by the bacterium Borrelia burgdorferi, is the most common tick-borne illness in the United States. Despite the rise in Lyme disease incidence, there is no vaccine against B. burgdorferi approved for human use. Little is known about the immune correlates of protection needed to prevent Lyme disease. In this work, a mouse model was used to characterize the immune response and compare the protection provided by two USDA-approved vaccines for use in canines: Duramune (bacterin vaccine) and Vanguard crLyme (subunit vaccine composed of two outer surface proteins, OspA and OspC). C3H/HeNCrl mice were immunized with two doses of either Duramune or Vanguard, and immune responses and protection against B. burgdorferi were assessed in short (35 days) and long-term (120 days) studies. Flow cytometry, ELISPOT detection of antibody-producing cells, and antibody affinity studies were performed to identify correlates of vaccine-mediated protection. Both vaccines induced humoral responses, with high IgG titers against B. burgdorferi. However, the levels of anti-B. burgdorferi antibodies decayed over time in Vanguard-vaccinated mice. While both vaccines triggered the production of antibodies against both OspA and OspC, antibody levels against these proteins were also lower in Vanguard-vaccinated mice 120 days post-vaccination. Both vaccines only provided partial protection against B. burgdorferi at the dose used in this model. The protection provided by Duramune was superior to Vanguard 120 days post-vaccination, and was characterized by higher antibody titers, higher abundance of long-lived plasma cells, and higher avidity antibodies than Vanguard. Overall, these studies provide insights into the importance of the humoral memory response to veterinary vaccines against Lyme disease and will help inform the development of future human vaccines.

Hitchhiker's Guide to Borrelia burgdorferi

Don't Panic. In the nearly 50 years since the discovery of Lyme disease, Borrelia burgdorferi has emerged as an unlikely workhorse of microbiology. Interest in studying host-pathogen interactions fueled significant progress in making the fastidious microbe approachable in laboratory settings, including the development of culture methods, animal models, and genetic tools. By developing these systems, insight has been gained into how the microbe is able to survive its enzootic cycle and cause human disease. Here, we discuss the discovery of B. burgdorferi and its development as a model organism before diving into the critical lessons we have learned about B. burgdorferi biology at pivotal stages of its lifecycle: gene expression changes during the tick blood meal, colonization of a new vertebrate host, and developing a long-lasting infection in that vertebrate until a new tick feeds. Our goal is to highlight the advancements that have facilitated B. burgdorferi research and identify gaps in our current understanding of the microbe.

Identification of Major Histocompatibility Complex Class II Epitopes From Lyme Autoantigen Apolipoprotein B-100 and Borrelia burgdorferi Mcp4 in Murine Lyme Arthritis

BACKGROUND

During infection with the Lyme arthritis (LA) pathogen Borrelia burgdorferi, T-cell responses to both host and pathogen are dysregulated, resulting in chronic infection and frequent development of autoimmunity.

METHODS

To assess CD4+ T-cell epitopes presented during development of LA, we used an unbiased, immunopeptidomics approach to characterize the major histocompatibility complex (MHC) class II immunopeptidome in B burgdorferi-infected C57BL/6 (B6) mice, which develop mild, self-limiting LA, and infected B6 Il10-/- mice, which develop severe, persistent LA at 0, 4, and 16 weeks postinfection (22-23 mice per group).

RESULTS

Peptides derived from proteins involved in adaptive T- and B-cell responses and cholesterol metabolism, including human Lyme autoantigen apolipoprotein B-100 (apoB-100), were enriched in infected Il10-/- mice; whereas peptides derived from proteins involved in neutrophil extracellular net formation were enriched in infected B6 mice. Presentation of apoB-100 peptides showed evidence of epitope expansion during infection. Of several identified B burgdorferi peptides, only 1, a methyl-accepting chemotaxis protein peptide Mcp4442-462, was immunogenic.

CONCLUSIONS

ApoB-100, a human Lyme autoantigen, undergoes marked epitope expansion during LA development. The paucity of immunogenic B burgdorferi epitopes supports previous findings suggesting CD4+ T-cell responses are suppressed in murine LA.

IL-12 induces a B cell-intrinsic IL-12/IFNγ feed-forward loop promoting extrafollicular B cell responses

While some infections elicit germinal centers, others produce only extrafollicular responses. The mechanisms controlling these dichotomous fates are poorly understood. We identify IL-12 as a cytokine switch, acting directly on B cells to promote extrafollicular and suppress germinal center responses. IL-12 initiates a B cell-intrinsic feed-forward loop between IL-12 and IFNγ, amplifying IFNγ production, which promotes proliferation and plasmablast differentiation from mouse and human B cells, in synergy with IL-12. IL-12 sustains the expression of a portion of IFNγ-inducible genes. Together, they also induce unique gene changes, reflecting both IFNγ amplification and cooperative effects between both cytokines. In vivo, cells lacking both IL-12 and IFNγ receptors are more impaired in plasmablast production than those lacking either receptor alone. Further, B cell-derived IL-12 enhances both plasmablast responses and T helper 1 cell commitment. Thus, B cell-derived IL-12, acting on T and B cells, determines the immune response mode, with implications for vaccines, pathogen protection and autoimmunity.

Therapeutic vaccine-induced plasma cell differentiation is defective in the presence of persistently high HBsAg levels

BACKGROUND & AIMS

Mechanisms behind the impaired response of antigen-specific B cells to therapeutic vaccination in chronic hepatitis B virus (HBV) infection remain unclear. The development of vaccines or strategies to overcome this obstacle is vital for advancing the management of chronic hepatitis B.

METHODS

A mouse model, denominated as E6F6-B, was engineered to feature a knock-in of a B-cell receptor (BCR) that specifically recognizes HBsAg. This model served as a valuable tool for investigating the temporal and spatial dynamics of humoral responses following therapeutic vaccination under continuous antigen exposure. Using a suite of immunological techniques, we elucidated the differentiation trajectory of HBsAg-specific B cells post-therapeutic vaccination in HBV carrier mice.

RESULTS

Utilizing the E6F6-B transfer model, we observed a marked decline in antibody-secreting cells 2 weeks after vaccination. A dysfunctional and atypical pre-plasma cell population (BLIMP-1+ IRF4+ CD40- CD138- BCMA-) emerged, manifested by sustained BCR signaling. By deploying an antibody to purge persistent HBsAg, we effectively prompted the therapeutic vaccine to provoke conventional plasma cell differentiation. This resulted in an enhanced anti-HBs antibody response and facilitated HBsAg clearance.

CONCLUSIONS

Sustained high levels of HBsAg limit the ability of therapeutic hepatitis B vaccines to induce the canonical plasma cell differentiation necessary for anti-HBs antibody production. Employing a strategy combining antibodies with vaccines can surmount this altered humoral response associated with atypical pre-plasma cells, leading to improved therapeutic efficacy in HBV carrier mice.

IMPACT AND IMPLICATIONS

Therapeutic vaccines aimed at combatting HBV encounter suboptimal humoral responses in clinical settings, and the mechanisms impeding their effectiveness have remained obscure. Our research, utilizing the innovative E6F6-B mouse transfer model, reveals that the persistence of HBsAg can lead to the emergence of an atypical pre-plasma cell population, which proves to be relevant to the potency of therapeutic HBV vaccines. Targeting the aberrant differentiation process of these atypical pre-plasma cells stands out as a critical strategy to amplify the humoral response elicited by HBV therapeutic vaccines in carrier mouse models. This discovery suggests a compelling avenue for further study in the context of human chronic hepatitis B. Encouragingly, our findings indicate that synergistic therapy combining HBV-specific antibodies with vaccines offers a promising approach that could significantly advance the pursuit of a functional cure for HBV.

Suppression of host humoral immunity by Borrelia burgdorferi varies over the course of infection

Borrelia burgdorferi, the spirochetal agent of Lyme disease, utilizes a variety of strategies to evade and suppress the host immune response, which enables it to chronically persist in the host. The resulting immune response is characterized by unusually strong IgM production and a lack of long-term protective immunity. Previous studies in mice have shown that infection with B. burgdorferi also broadly suppresses host antibody responses against unrelated antigens. Here, we show that mice infected with B. burgdorferi and concomitantly immunized with recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein had an abrogated antibody response to the immunization. To further define how long this humoral immune suppression lasts, mice were immunized at 2, 4, and 6 weeks post-infection. Suppression of host antibody production against the SARS-CoV-2 spike protein peaked at 2 weeks post-infection but continued for all timepoints measured. Antibody responses against the SARS-CoV-2 spike protein were also assessed following antibiotic treatment to determine whether this immune suppression persists or resolves following clearance of B. burgdorferi. Host antibody production against the SARS-CoV-2 spike protein returned to baseline following antibiotic treatment; however, anti-SARS-CoV-2 IgM remained high, comparable to levels found in B. burgdorferi-infected but untreated mice. Thus, our data demonstrate restored IgG responses following antibiotic treatment but persistently elevated IgM levels, indicating lingering effects of B. burgdorferi infection on the immune system following treatment.

Host glycosylation of immunoglobulins impairs the immune response to acute Lyme disease

BACKGROUND

Lyme disease is caused by the bacteria Borreliella burgdorferi sensu lato (Bb) transmitted to humans from the bite of an infected Ixodes tick. Current diagnostics for Lyme disease are insensitive at the early disease stage and they cannot differentiate between active infections and people with a recent history of antibiotic-treated Lyme disease.

METHODS

Machine learning technology was utilized to improve the prediction of acute Lyme disease and identify sialic acid and galactose sugar structures (N-glycans) on immunoglobulins associated specifically at time points during acute Lyme disease time. A plate-based approach was developed to analyze sialylated N-glycans associated with anti-Bb immunoglobulins. This multiplexed approach quantitates the abundance of Bb-specific IgG and the associated sialic acid, yielding an accuracy of 90% in a powered study.

FINDINGS

It was demonstrated that immunoglobulin sialic acid levels increase during acute Lyme disease and following antibiotic therapy and a 3-month convalescence, the sialic acid level returned to that found in healthy control subjects (p < 0.001). Furthermore, the abundance of sialic acid on Bb-specific IgG during acute Lyme disease impaired the host's ability to combat Lyme disease via lymphocytic receptor FcγRIIIa signaling. After enzymatically removing the sialic acid present on Bb-specific antibodies, the induction of cytotoxicity from acute Lyme disease patient antigen-specific IgG was significantly improved.

INTERPRETATION

Taken together, Bb-specific immunoglobulins contain increased sialylation which impairs the host immune response during acute Lyme disease. Furthermore, this Bb-specific immunoglobulin sialyation found in acute Lyme disease begins to resolve following antibiotic therapy and convalescence.

FUNDING

Funding for this study was provided by the Coulter-Drexel Translational Research Partnership Program as well as from a Faculty Development Award from the Drexel University College of Medicine Institute for Molecular Medicine and Infectious Disease and the Department of Microbiology and Immunology.

Highly heterogenous humoral immune response in Lyme disease patients revealed by broad machine learning-assisted antibody binding profiling with random peptide arrays

Introduction

Lyme disease (LD), a rapidly growing public health problem in the US, represents a formidable challenge due to the lack of detailed understanding about how the human immune system responds to its pathogen, the Borrelia burgdorferi bacterium. Despite significant advances in gaining deeper insight into mechanisms the pathogen uses to evade immune response, substantial gaps remain. As a result, molecular tools for the disease diagnosis are lacking with the currently available tests showing poor performance. High interpersonal variability in immune response combined with the ability of the pathogen to use a number of immune evasive tactics have been implicated as underlying factors for the limited test performance.

Methods

This study was designed to perform a broad profiling of the entire repertoire of circulating antibodies in human sera at the single-individual level using planar arrays of short linear peptides with random sequences. The peptides sample sparsely, but uniformly the entire combinatorial sequence space of the same length peptides for profiling the humoral immune response to a B.burg. infection and compare them with other diseases with etiology similar to LD and healthy controls.

Results

The study revealed substantial variability in antibody binding profiles between individual LD patients even to the same antigen (VlsE protein) and strong similarity between individuals diagnosed with Lyme disease and healthy controls from the areas endemic to LD suggesting a high prevalence of seropositivity in endemic healthy control.

Discussion

This work demonstrates the utility of the approach as a valuable analytical tool for agnostic profiling of humoral immune response to a pathogen.

Microbes and Mental Illness: Past, Present, and Future

A review of the association between microbes and mental illness is performed, including the history, relevant definitions, infectious agents associated with mental illnesses, complex interactive infections, total load theory, pathophysiology, psychoimmunology, psychoneuroimmunology, clinical presentations, early-life infections, clinical assessment, and treatment. Perspectives on the etiology of mental illness have evolved from demonic possession toward multisystem biologically based models that include gene expression, environmental triggers, immune mediators, and infectious diseases. Microbes are associated with a number of mental disorders, including autism, schizophrenia, bipolar disorder, depressive disorders, and anxiety disorders, as well as suicidality and aggressive or violent behaviors. Specific microbes that have been associated or potentially associated with at least one of these conditions include Aspergillus, Babesia, Bartonella, Borna disease virus, Borrelia burgdorferi (Lyme disease), Candida, Chlamydia, coronaviruses (e.g., SARS-CoV-2), Cryptococcus neoformans, cytomegalovirus, enteroviruses, Epstein-Barr virus, hepatitis C, herpes simplex virus, human endogenous retroviruses, human immunodeficiency virus, human herpesvirus-6 (HHV-6), human T-cell lymphotropic virus type 1, influenza viruses, measles virus, Mycoplasma, Plasmodium, rubella virus, Group A Streptococcus (PANDAS), Taenia solium, Toxoplasma gondii, Treponema pallidum (syphilis), Trypanosoma, and West Nile virus. Recognition of the microbe and mental illness association with the development of greater interdisciplinary research, education, and treatment options may prevent and reduce mental illness morbidity, disability, and mortality.

Borrelia burgdorferi Infection-Induced Persistent IgM Secretion Controls Bacteremia, but Not Bacterial Dissemination or Tissue Burden

Infection with Borrelia burgdorferi causes Lyme disease in humans. In small rodents, the natural reservoir species of this spirochete, infections lead to only modest disease manifestations, despite causing persistence infection. Although B cell responses are central for controlling bacterial tissue burden and disease manifestations, they lack classical aspects of T-dependent responses, such as sustained IgG affinity maturation and longevity, corresponding with a rapid collapse of germinal centers. Instead, the Ab response is characterized by strong and ongoing secretion of IgM, whose origins and impact on protective immunity to B. burgdorferi remain unknown. In this article, we demonstrate that B. burgdorferi infection-induced IgM in mice was produced continuously, mainly by conventional B, not B-1 cells, in a T-independent manner. Although IgM was passively protective and restricted early bacteremia, its production had no effects on bacterial dissemination into solid tissues, nor did it affect Borrelia tissue burden. The latter was controlled by the induction of bactericidal IgG, as shown comparing infections in wild type mice with those of mice lacking exclusively secreted IgM-/-, all class-switched Abs via deletion of aicda (AID-/-), and all secreted Abs (secreted IgM-/- × AID-/-). Consistent with the notion that B. burgdorferi infection drives production of IgM over more tissue-penetrable IgG, we demonstrated increased short- and long-term IgM Ab responses also to a coadministered, unrelated Ag. Thus, the continued production of IgM may explain the absence of B. burgdorferi in the blood.

Antigen-Specific CD4 T Cell and B Cell Responses to Borrelia burgdorferi

Long-lived T-dependent B cell responses fail to develop during persistent infection of mice with Borrelia burgdorferi, the causative agent of Lyme disease, raising questions about the induction and/or functionality of anti-B. burgdorferi adaptive immune responses. Yet, a lack of reagents has limited investigations into B. burgdorferi-specific T and B cells. We attempted two approaches to track B. burgdorferi-induced CD4 T cells. First, a B. burgdorferi mutant was generated with an influenza hemagglutinin (HA) peptide, HA111-119, inserted into the B. burgdorferi arthritis-related protein (Arp) locus. Although this B. burgdorferi arp::HA strain remained infectious, peptide-specific TCR transgenic CD4 T cells in vitro, or adoptively transferred into B. burgdorferi arp::HA-infected BALB/c mice, did not clonally expand above those of recipients infected with the parental B. burgdorferi strain or a B. burgdorferi mutant containing an irrelevant peptide. Some expansion, however, occurred in B. burgdorferi arp::HA-infected BALB/c SCID mice. Second, a (to our knowledge) newly identified I-Ab-restricted CD4 T cell epitope, Arp152-166, was used to generate Arp MHC class II tetramers. Flow cytometry showed small numbers of Arp-specific CD4 T cells emerging in mice infected with B. burgdorferi but not with Arp-deficient Borrelia afzelii. Although up to 30% of Arp-specific CD4 T cells were ICOS+PD-1+CXCR5+BCL6+ T follicular helper cells, their numbers declined after day 12, before germinal centers (GCs) are prominent. Although some Arp-specific B cells, identified using fluorochrome-labeled rArp proteins, had the phenotype of GC B cells, their frequencies did not correlate with anti-Arp serum IgG. The data suggest a failure not in the induction, but in the maintenance of GC T follicular helper and/or B cells to B. burgdorferi.

Alterations in germinal center formation and B cell activation during severe Orientia tsutsugamushi infection in mice

Scrub typhus is a poorly studied but life-threatening disease caused by the intracellular bacterium Orientia tsutsugamushi (Ot). Cellular and humoral immunity in Ot-infected patients is not long-lasting, waning as early as one-year post-infection; however, its underlying mechanisms remain unclear. To date, no studies have examined germinal center (GC) or B cell responses in Ot-infected humans or experimental animals. This study was aimed at evaluating humoral immune responses at acute stages of severe Ot infection and possible mechanisms underlying B cell dysfunction. Following inoculation with Ot Karp, a clinically dominant strain known to cause lethal infection in C57BL/6 mice, we measured antigen-specific antibody titers, revealing IgG2c as the dominant isotype induced by infection. Splenic GC responses were evaluated by immunohistology, co-staining for B cells (B220), T cells (CD3), and GCs (GL-7). Organized GCs were evident at day 4 post-infection (D4), but they were nearly absent at D8, accompanied by scattered T cells throughout splenic tissues. Flow cytometry revealed comparable numbers of GC B cells and T follicular helper (Tfh) cells at D4 and D8, indicating that GC collapse was not due to excessive death of these cell subtypes at D8. B cell RNAseq analysis revealed significant differences in expression of genes associated with B cell adhesion and co-stimulation at D8 versus D4. The significant downregulation of S1PR2 (a GC-specific adhesion gene) was most evident at D8, correlating with disrupted GC formation. Signaling pathway analysis uncovered downregulation of 71% of B cell activation genes at D8, suggesting attenuation of B cell activation during severe infection. This is the first study showing the disruption of B/T cell microenvironment and dysregulation of B cell responses during Ot infection, which may help understand the transient immunity associated with scrub typhus.

Erp and Rev Adhesins of the Lyme Disease Spirochete's Ubiquitous cp32 Prophages Assist the Bacterium during Vertebrate Infection

Almost all spirochetes in the genus Borrelia (sensu lato) naturally contain multiple variants of closely related prophages. In the Lyme disease borreliae, these prophages are maintained as circular episomes that are called circular plasmid 32 kb (cp32s). The cp32s of Lyme agents are particularly unique in that they encode two distinct families of lipoproteins, namely, Erp and Rev, that are expressed on the bacterial outer surface during infection of vertebrate hosts. All identified functions of those outer surface proteins involve interactions between the spirochetes and host molecules, as follows: Erp proteins bind plasmin(ogen), laminin, glycosaminoglycans, and/or components of complement and Rev proteins bind fibronectin. Thus, cp32 prophages provide their bacterial hosts with surface proteins that can enhance infection processes, thereby facilitating their own survival. Horizontal transfer via bacteriophage particles increases the spread of beneficial alleles and creates diversity among Erp and Rev proteins.

Bystander activation of Bordetella pertussis-induced nasal tissue-resident memory CD4 T cells confers heterologous immunity to Klebsiella pneumoniae

Tissue-resident memory CD4 T (T_RM ) cells induced by infection with Bordetella pertussis persist in respiratory tissues and confer long-term protective immunity against reinfection. However, it is not clear how they are maintained in respiratory tissues. Here, we demonstrate that B. pertussis-specific CD4 T_RM cells produce IL-17A in response to in vitro stimulation with LPS or heat-killed Klebsiella pneumoniae (HKKP) in the presence of dendritic cells. Furthermore, IL-17A-secreting CD4 T_RM cells expand in the lung and nasal tissue of B. pertussis convalescent mice following in vivo administration of LPS or HKKP. Bystander activation of CD4 T_RM cells was suppressed by anti-IL-12p40 but not by anti-MHCII antibodies. Furthermore, purified respiratory tissue-resident, but not circulating, CD4 T cells from convalescent mice produced IL-17A following direct stimulation with IL-23 and IL-1β or IL-18. Intranasal immunization of mice with a whole-cell pertussis vaccine induced respiratory CD4 T_RM cells that were reactivated following stimulation with K. pneumoniae. Furthermore, the nasal pertussis vaccine conferred protective immunity against B. pertussis but also attenuated infection with K. pneumoniae. Our findings demonstrate that CD4 T_RM cells induced by respiratory infection or vaccination can undergo bystander activation and confer heterologous immunity to an unrelated respiratory pathogen.

Immune evasion strategies of major tick-transmitted bacterial pathogens

Tick-transmitted bacterial pathogens thrive in enzootic infection cycles, colonizing disparate vertebrate and arthropod tissues, often establishing persistent infections. Therefore, the evolution of robust immune evasion strategies is central to their successful persistence or transmission between hosts. To survive in nature, these pathogens must counteract a broad range of microbicidal host responses that can be localized, tissue-specific, or systemic, including a mix of these responses at the host-vector interface. Herein, we review microbial immune evasion strategies focusing on Lyme disease spirochetes and rickettsial or tularemia agents as models for extracellular and intracellular tick-borne pathogens, respectively. A better understanding of these adaptive strategies could enrich our knowledge of the infection biology of relevant tick-borne diseases, contributing to the development of future preventions.

Correlation between COVID-19 severity and previous exposure of patients to Borrelia spp

Predictors for the risk of severe COVID-19 are crucial for patient care and control of the disease. Other infectious diseases as potential comorbidities in SARS-CoV-2 infection are still poorly understood. Here we identify association between the course of COVID-19 and Lyme disease (borreliosis), caused by Borrelia burgdorferi transmitted to humans by ticks. Exposure to Borrelia was identified by multi-antigenic (19 antigens) serological testing of patients: severe COVID-19 (hospitalized), asymptomatic to mild COVID-19 (home treated or not aware of being infected), and not infected with SARS-CoV-2. Increased levels of Borrelia-specific IgGs strongly correlated with COVID-19 severity and risk of hospitalization. This suggests that a history of tick bites and related infections may contribute to the risks in COVID-19. Though mechanisms of this link is not clear yet, screening for antibodies targeting Borrelia may help accurately assess the odds of hospitalization for SARS-CoV-2 infected patients, supporting efforts for efficient control of COVID-19.

Mitochondrial regulation of acute extrafollicular B-cell responses to COVID-19 severity

BACKGROUND

Patients with COVID-19 display a broad spectrum of manifestations from asymptomatic to life-threatening disease with dysregulated immune responses. Mechanisms underlying the detrimental immune responses and disease severity remain elusive.

METHODS

We investigated a total of 137 APs infected with SARS-CoV-2. Patients were divided into mild and severe patient groups based on their requirement of oxygen supplementation. All blood samples from APs were collected within three weeks after symptom onset. Freshly isolated PBMCs were investigated for B cell subsets, their homing potential, activation state, mitochondrial functionality and proliferative response. Plasma samples were tested for cytokine concentration, and titer of Nabs, RBD-, S1-, SSA/Ro- and dsDNA-specific IgG.

RESULTS

While critically ill patients displayed predominantly extrafollicular B cell activation with elevated inflammation, mild patients counteracted the disease through the timely induction of mitochondrial dysfunction in B cells within the first week post symptom onset. Rapidly increased mitochondrial dysfunction, which was caused by infection-induced excessive intracellular calcium accumulation, suppressed excessive extrafollicular responses, leading to increased neutralizing potency index and decreased inflammatory cytokine production. Patients who received prior COVID-19 vaccines before infection displayed significantly decreased extrafollicular B cell responses and mild disease.

CONCLUSION

Our results reveal an immune mechanism that controls SARS-CoV-2-induced detrimental B cell responses and COVID-19 severity, which may have implications for viral pathogenesis, therapeutic interventions and vaccine development.

Acute lyme disease IgG N-linked glycans contrast the canonical inflammatory signature

Lyme disease (LD) infection is caused by Borrelia burgdorferi sensu lato (Bb). Due to the limited presence of this pathogen in the bloodstream in humans, diagnosis of LD relies on seroconversion. Immunoglobulins produced in response to infection are differentially glycosylated to promote or inhibit downstream inflammatory responses by the immune system. Immunoglobulin G (IgG) N-glycan responses to LD have not been characterized. In this study, we analyzed IgG N-glycans from cohorts of healthy controls, acute LD patient serum, and serum collected after acute LD patients completed a 2- to 3-week course of antibiotics and convalesced for 70-90 days. Results indicate that during the acute phase of Bb infection, IgG shifts its glycosylation profile to include structures that are not associated with the classic proinflammatory IgG N-glycan signature. This unexpected result is in direct contrast to what is reported for other inflammatory diseases. Furthermore, IgG N-glycans detected during acute LD infection discriminated between control, acute, and treated cohorts with a sensitivity of 75-100% and specificity of 94.7-100%.

Recent Advances in the Immunologic Method Applied to Tick-Borne Diseases in Brazil

Zoonotic-origin infectious diseases are one of the major concerns of human and veterinary health systems. Ticks, as vectors of several zoonotic diseases, are ranked second only to mosquitoes as vectors. Many ticks’ transmitted infections are still endemic in the Americas, Europe, and Africa and represent approximately 17% of their infectious diseases population. Although our scientific capacity to identify and diagnose diseases is increasing, it remains a challenge in the case of tick-borne conditions. For example, in 2017, 160 cases of the Brazilian Spotted Fever (BSF, a tick-borne illness) were confirmed, alarming the notifiable diseases information system. Conversely, Brazilian borreliosis and ehrlichiosis do not require notification. Still, an increasing number of cases in humans and dogs have been reported in southeast and northeastern Brazil. Immunological methods applied to human and dog tick-borne diseases (TBD) show low sensitivity and specificity, cross-reactions, and false IgM positivity. Thus, the diagnosis and management of TBD are hampered by the personal tools and indirect markers used. Therefore, specific and rapid methods urgently need to be developed to diagnose the various types of tick-borne bacterial diseases. This review presents a brief historical perspective on the evolution of serological assays and recent advances in diagnostic tests for TBD (ehrlichiosis, BSF, and borreliosis) in humans and dogs, mainly applied in Brazil. Additionally, this review covers the emerging technologies available in diagnosing TBD, including biosensors, and discusses their potential for future use as gold standards in diagnosing these diseases.

Serological Analysis Identifies Consequential B Cell Epitopes on the Flexible Linker and C-Terminus of Decorin Binding Protein A (DbpA) from Borrelia burgdorferi

Decorin binding protein A (DbpA) is a surface adhesin of Borrelia burgdorferi, the causative agent of Lyme disease. While DbpA is one of the most immunogenic of B. burgdorferi’s nearly 100 lipoproteins, the B cell epitopes on DbpA recognized by humans following B. burgdorferi infection have not been fully elucidated. In this report we profiled ~270 B. burgdorferi-seropositive human serum samples for IgM and IgG reactivity with a tiled DbpA 18-mer peptide array derived from B. burgdorferisensu stricto strains B31 and 297. Using enzyme-linked immunosorbent assays (ELISA) and multiplex immunoassays (MIA), we identified 12 DbpA-derived peptides whose antibody reactivities were significantly elevated (generally <10-fold) in B. burgdorferi-seropositive sera, compared to those measured in a healthy cohort. The most reactive peptide (>80-fold IgG, 10-fold IgM) corresponded to residues 64 to 81, which map to an exposed flexible loop between DbpA’s α-helix 1 and α-helix 2. This loop, whose sequence is identical between strains B31 and 297, overhangs DbpA’s substrate binding pocket. A second strongly reactive antibody target (>80-fold IgG, 3 to 5-fold IgM) mapped to DbpA’s C-terminus, a lysine rich tail implicated in attachment to glycosaminoglycans. We postulate that antibody responses against these two targets on DbpA could limit B.burgdorferi’s ability to attach to and colonize distal tissues during the early stages of infection.

IMPORTANCE The bacterium, Borrelia burgdorferi, is the causative agent of Lyme disease, the most reported tick-borne illness in the United States. In humans, clinical manifestations of Lyme disease are complex and can persist for months, even in the face of a robust antibody response directed against numerous B. burgdorferi surface proteins, including decorin binding protein A (DbpA), which is involved in the early stages of infection. In this study we employed ~270 serum samples from B. burgdorferi-seropositive individuals to better understand human antibody reactivity to specific regions (called epitopes) of DbpA and how such antibodies may function in limiting B. burgdorferi dissemination and tissue colonization.

CD4 T cell responses in persistent Borrelia burgdorferi infection

Infection of mice with Borrelia burgdorferi (Bb), a tick-transmitted spirochete and the pathogen that causes Lyme disease in humans, triggers CD4 T cell activation in secondary lymphoid tissues, from which they disseminate into various infected tissues. Despite their activation and the appearance of CD4 T cell-dependent antibody responses, Bb establishes persistent infection in natural Bb reservoir hosts in the absence of overt disease, raising the question of the effectiveness of the anti-Bb T cell responses. Reviewing the existing literature, we propose that CD4 T cells might constitute a host cell target of Bb-mediated immune evasion, rendering these cells ineffective in orchestrating effective inflammatory responses and in supporting highly functional Bb-specific antibody induction. Supporting the induction of more effective CD4 T cell responses may help overcome Bb persistence.

Bacterial infection disrupts established germinal center reactions through monocyte recruitment and impaired metabolic adaptation

Consecutive exposures to different pathogens are highly prevalent and often alter the host immune response. However, it remains unknown how a secondary bacterial infection affects an ongoing adaptive immune response elicited against primary invading pathogens. We demonstrated that recruitment of Sca-1+ monocytes into lymphoid organs during Salmonella Typhimurium (STm) infection disrupted pre-existing germinal center (GC) reactions. GC responses induced by influenza, plasmodium, or commensals deteriorated following STm infection. GC disruption was independent of the direct bacterial interactions with B cells and instead was induced through recruitment of CCR2-dependent Sca-1+ monocytes into the lymphoid organs. GC collapse was associated with impaired cellular respiration and was dependent on TNFα and IFNγ, the latter of which was essential for Sca-1+ monocyte differentiation. Monocyte recruitment and GC disruption also occurred during LPS-supplemented vaccination and Listeria monocytogenes infection. Thus, systemic activation of the innate immune response upon severe bacterial infection is induced at the expense of antibody-mediated immunity.

Borrelia burgdorferi and Borrelia miyamotoi in Atlantic Canadian wildlife

Borrelia burgdorferi and Borrelia miyamotoi are tick-vectored zoonotic pathogens maintained in wildlife species. Tick populations are establishing in new areas globally in response to climate change and other factors. New Brunswick is a Canadian maritime province at the advancing front of tick population establishment and has seen increasing numbers of ticks carrying B. burgdorferi, and more recently B. miyamotoi. Further, it is part of a region of Atlantic Canada with wildlife species composition differing from much of continental North America and little information exists as to the presence and frequency of infection of Borrelia spp. in wildlife in this region. We used a citizen science approach to collect a wide range of animals including migratory birds, medium-sized mammals, and small mammals. In total we tested 339 animals representing 20 species for the presence of B. burgdorferi and B. miyamotoi. We have developed new nested PCR primers and a protocol with excellent specificity for detecting both of these Borrelia species, both single and double infections, in tissues and organs of various wildlife species. The positive animals were primarily small non-migratory mammals, approximately twice as many were infected with B. burgdorferi than B. miyamotoi and one animal was found infected with both. In addition to established reservoir species, the jumping mouse (Napaeozapus insignis) was found frequently infected; this species had the highest infection prevalence for both B. burgdorferi and B. miyamotoi and has not previously been identified as an important carrier for either Borrelia species. Comprehensive testing of tissues found that all instances of B. burgdorferi infection were limited to one tissue within the host, whereas two of the five B. miyamotoi infections were diffuse and found in multiple systems. In the one coinfected specimen, two fetuses were also recovered and found infected with B. miyamotoi. This presumptive transplacental transmission suggests that vertical transmission in mammals is possible. This finding implies that B. miyamotoi could rapidly spread into wildlife populations, as well as having potential human health implications.

Real time micro-organisms PCR in 104 patients with polymorphic signs and symptoms that may be related to a tick bite

INTRODUCTION

Ticks are frequently polyinfected and can thus transmit numerous microorganisms. A large number of bacteria, parasites and viruses are transmitted by tick bites and could cause different signs and symptoms in patients. The main goal of this study was to search for these numerous microorganisms in patients presenting with persistent polymorphic syndrome possibly due to a tick bite (SPPT).

PATIENTS AND METHODS

The following microorganisms were searched for in saliva, urine, venous and capillary blood by using real time PCR: Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Borrelia hermsii, Bartonella spp., Bartonella quintana, Bartonella henselae, Ehrlichia spp., Anaplasma spp., Rickettsia spp., Coxiella burnetii, Brucella spp., Francisella tularensis, Mycoplasma spp., Chlamydia spp., Babesia spp., Theileria spp.

RESULTS

104 patients were included. 48% of the patients were poly-infected, and 25% harboured at least three different microorganisms. Borrelia spp. were not the most frequent bacteria observed, observed far behind Mycoplasma spp., Rickettsia spp. and Ehrlichia spp. which were the most frequent microorganisms observed. Piroplasms were found in a significant number of patients. The most sensitive matrix was saliva, followed by urine, capillary blood and venous blood.

CONCLUSION

Our prospective study has shown that patients with SPPT, a syndrome close to fibromyalgia, could harbour several tick borne microorganisms.

Plasma cell survival: The intrinsic drivers, migratory signals, and extrinsic regulators

Antibody-secreting cells (ASC) are the effectors of protective humoral immunity and the only cell type that produces antibodies or immunoglobulins in mammals. In addition to their formidable capacity to secrete massive quantities of proteins, ASC are terminally differentiated and have unique features to become long-lived plasma cells (LLPC). Upon antigen encounter, B cells are activated through a complex multistep process to undergo fundamental morphological, subcellular, and molecular transformation to become an efficient protein factory with lifelong potential. The ASC survival potential is determined by factors at the time of induction, capacity to migration from induction to survival sites, and ability to mature in the specialized bone marrow microenvironments. In the past decade, considerable progress has been made in identifying factors regulating ASC longevity. Here, we review the intrinsic drivers, trafficking signals, and extrinsic regulators with particular focus on how they impact the survival potential to become a LLPC.

Extrafollicular IgD+ B cells generate IgE antibody secreting cells in the nasal mucosa

Increased IgE is a typical feature of allergic rhinitis. Local class-switch recombination has been intimated but B cell precursors and mechanisms remain elusive. Here we describe the dynamics underlying the generation of IgE-antibody secreting cells (ASC) in human nasal polyps (NP), mucosal tissues rich in ASC without germinal centers (GC). Using VH next generation sequencing, we identified an extrafollicular (EF) mucosal IgD+ naïve-like intermediate B cell population with high connectivity to the mucosal IgE ASC. Mucosal IgD+ B cells, express germline epsilon transcripts and predominantly co-express IgM. However, a small but significant fraction co-express IgG or IgA instead which also show connectivity to ASC IgE. Phenotypically, NP IgD+ B cells display an activated profile and molecular evidence of BCR engagement. Transcriptionally, mucosal IgD+ B cells reveal an intermediate profile between naïve B cells and ASC. Single cell IgE ASC analysis demonstrates lower mutational frequencies relative to IgG, IgA, and IgD ASC consistent with IgE ASC derivation from mucosal IgD+ B cell with low mutational load. In conclusion, we describe a novel mechanism of GC-independent, extrafollicular IgE ASC formation at the nasal mucosa whereby activated IgD+ naïve B cells locally undergo direct and indirect (through IgG and IgA), IgE class switch.

Single-cell immunophenotyping of the skin lesion erythema migrans identifies IgM memory B cells

The skin lesion erythema migrans (EM) is an initial sign of the Ixodes tick-transmitted Borreliella spirochetal infection known as Lyme disease. T cells and innate immune cells have previously been shown to predominate the EM lesion and promote the reaction. Despite the established importance of B cells and antibodies in preventing infection, the role of B cells in the skin immune response to Borreliella is unknown. Here, we used single-cell RNA-Seq in conjunction with B cell receptor (BCR) sequencing to immunophenotype EM lesions and their associated B cells and BCR repertoires. We found that B cells were more abundant in EM in comparison with autologous uninvolved skin; many were clonally expanded and had circulating relatives. EM-associated B cells upregulated the expression of MHC class II genes and exhibited preferential IgM isotype usage. A subset also exhibited low levels of somatic hypermutation despite a gene expression profile consistent with memory B cells. Our study demonstrates that single-cell gene expression with paired BCR sequencing can be used to interrogate the sparse B cell populations in human skin and reveals that B cells in the skin infection site in early Lyme disease expressed a phenotype consistent with local antigen presentation and antibody production.

Short- and Long-Lived Autoantibody-Secreting Cells in Autoimmune Neurological Disorders

As B cells differentiate into antibody-secreting cells (ASCs), short-lived plasmablasts (SLPBs) are produced by a primary extrafollicular response, followed by the generation of memory B cells and long-lived plasma cells (LLPCs) in germinal centers (GCs). Generation of IgG4 antibodies is T helper type 2 (Th2) and IL-4, -13, and -10-driven and can occur parallel to IgE, in response to chronic stimulation by allergens and helminths. Although IgG4 antibodies are non-crosslinking and have limited ability to mobilize complement and cellular cytotoxicity, when self-tolerance is lost, they can disrupt ligand-receptor binding and cause a wide range of autoimmune disorders including neurological autoimmunity. In myasthenia gravis with predominantly IgG4 autoantibodies against muscle-specific kinase (MuSK), it has been observed that one-time CD20⁺ B cell depletion with rituximab commonly leads to long-term remission and a marked reduction in autoantibody titer, pointing to a short-lived nature of autoantibody-secreting cells. This is also observed in other predominantly IgG4 autoantibody-mediated neurological disorders, such as chronic inflammatory demyelinating polyneuropathy and autoimmune encephalitis with autoantibodies against the Ranvier paranode and juxtaparanode, respectively, and extends beyond neurological autoimmunity as well. Although IgG1 autoantibody-mediated neurological disorders can also respond well to rituximab induction therapy in combination with an autoantibody titer drop, remission tends to be less long-lasting and cases where titers are refractory tend to occur more often than in IgG4 autoimmunity. Moreover, presence of GC-like structures in the thymus of myasthenic patients with predominantly IgG1 autoantibodies against the acetylcholine receptor and in ovarian teratomas of autoimmune encephalitis patients with predominantly IgG1 autoantibodies against the N‐methyl‐d‐aspartate receptor (NMDAR) confers increased the ability to generate LLPCs. Here, we review available information on the short-and long-lived nature of ASCs in IgG1 and IgG4 autoantibody-mediated neurological disorders and highlight common mechanisms as well as differences, all of which can inform therapeutic strategies and personalized medical approaches.

Report of the Pathogenesis and Pathophysiology of Lyme Disease Subcommittee of the HHS Tick Borne Disease Working Group

An understanding of the pathogenesis and pathophysiology of Lyme disease is key to the ultimate care of patients with Lyme disease. To better understand the various mechanisms underlying the infection caused by Borrelia burgdorferi, the Pathogenesis and Pathophysiology of Lyme Disease Subcommittee was formed to review what is currently known about the pathogenesis and pathophysiology of Lyme disease, from its inception, but also especially about its ability to persist in the host. To that end, the authors of this report were assembled to update our knowledge about the infectious process, identify the gaps that exist in our understanding of the process, and provide recommendations as to how to best approach solutions that could lead to a better means to manage patients with persistent Lyme disease.

Germinal Center and Extrafollicular B Cell Responses in Vaccination, Immunity, and Autoimmunity

Activated B cells participate in either extrafollicular (EF) or germinal center (GC) responses. Canonical responses are composed of a short wave of plasmablasts (PBs) arising from EF sites, followed by GC producing somatically mutated memory B cells (MBC) and long-lived plasma cells. However, somatic hypermutation (SHM) and affinity maturation can take place at both sites, and a substantial fraction of MBC are produced prior to GC formation. Infection responses range from GC responses that persist for months to persistent EF responses with dominant suppression of GCs. Here, we review the current understanding of the functional output of EF and GC responses and the molecular switches promoting them. We discuss the signals that regulate the magnitude and duration of these responses, and outline gaps in knowledge and important areas of inquiry. Understanding such molecular switches will be critical for vaccine development, interpretation of vaccine efficacy and the treatment for autoimmune diseases.

Assessing the Need for Multiplex and Multifunctional Tick-Borne Disease Test in Routine Clinical Laboratory Samples from Lyme Disease and Febrile Patients with a History of a Tick Bite

Human polymicrobial infections in tick-borne disease (TBD) patients is an emerging public health theme. However, the requirement for holistic TBD tests in routine clinical laboratories is ambiguous. TICKPLEX® PLUS is a holistic TBD test utilized herein to assess the need for multiplex and multifunctional diagnostic tools in a routine clinical laboratory. The study involved 150 specimens categorized into Lyme disease (LD)-positive (n = 48), LD-negative (n = 30), and febrile patients from whom borrelia serology was requested (n = 72, later "febrile patients") based on reference test results from United Medix, Finland. Reference tests from DiaSorin, Immunetics, and Mikrogen Diagnostik followed the two-tier LD testing system. A comparison between the reference tests and TICKPLEX® PLUS produced 86%, 88%, and 87% positive, negative, and overall agreement, respectively. Additionally, up to 15% of LD and 11% of febrile patients responded to TBD related coinfections and opportunistic microbes. The results demonstrated that one (TICKPLEX® PLUS) test can aid in a LD diagnosis instead of four tests. Moreover, TBD is not limited to just LD, as the specimens produced immune responses to several TBD microbes. Lastly, the study indicated that the screening of febrile patients for TBDs could be a missed opportunity at reducing unreported patient cases.

The Brilliance of Borrelia: Mechanisms of Host Immune Evasion by Lyme Disease-Causing Spirochetes

Lyme disease (LD) has become the most common vector-borne illness in the northern hemisphere. The causative agent, Borrelia burgdorferi sensu lato, is capable of establishing a persistent infection within the host. This is despite the activation of both the innate and adaptive immune responses. B. burgdorferi utilizes several immune evasion tactics ranging from the regulation of surface proteins, tick saliva, antimicrobial peptide resistance, and the disabling of the germinal center. This review aims to cover the various methods by which B. burgdorferi evades detection and destruction by the host immune response, examining both the innate and adaptive responses. By understanding the methods employed by B. burgdorferi to evade the host immune response, we gain a deeper knowledge of B. burgdorferi pathogenesis and Lyme disease, and gain insight into how to create novel, effective treatments.

The Shaping of a B Cell Pool Maximally Responsive to Infections

B cell subsets differ in development, tissue distribution, and mechanisms of activation. In response to infections, however, all can differentiate into extrafollicular plasmablasts that rapidly provide highly protective antibodies, indicating that these plasmablasts are the main humoral immune response effectors. Yet, the effectiveness of this response type depends on the presence of antigen-specific precursors in the circulating mature B cell pool, a pool that is generated initially through the stochastic processes of B cell receptor assembly. Importantly, germinal centers then mold the repertoire of this B cell pool to be increasingly responsive to pathogens by generating a broad array of antimicrobial memory B cells that act as highly effective precursors of extrafollicular plasmablasts. Such B cell repertoire molding occurs in two ways: continuously via the chronic germinal centers of mucosal lymphoid tissues, driven by the presence of the microbiome, and via de novo generated germinal centers following acute infections. For effectively evaluating humoral immunity as a correlate of immune protection, it might be critical to measure memory B cell pools in addition to antibody titers.

VANGUARD®crLyme: A next generation Lyme disease vaccine that prevents B. burgdorferi infection in dogs

Lyme disease, a public health threat of significance to both veterinary and human medicine, is caused by the tick (Ixodes) transmitted spirochete, Borreliella burgdorferi. Here we report on the immunogenicity and efficacy of VANGUARD®crLyme (Zoetis), the most recent canine Lyme disease vaccine to be approved by the United States Department of Agriculture. VANGUARD®crLyme is a subunit vaccine consisting of outer surface protein A (OspA) and a recombinant outer surface protein C (OspC) based-chimeric epitope protein (chimeritope) that consists of at least 14 different linear epitopes derived from diverse OspC proteins. The combination of OspA and the OspC chimeritope (Ch14) in the vaccine formulation allows for the development of humoral immune responses that work synergistically to target spirochetes in both ticks and in mammals. Immunogenicity was assessed in purpose-bred dogs. A two-dose vaccination protocol resulted in high antibody titers to OspA and Ch14 and vaccinal antibody reacted with 25 different recombinant OspC variants. Efficacy was demonstrated using an Ixodes scapularis -purpose bred dog challenge model. Vaccination with VANGUARD®crLyme provided protection against infection and prevented the development of clinical manifestations and histopathological changes associated with Lyme disease.

Immune Response to Borrelia: Lessons from Lyme Disease Spirochetes

The mammalian host responds to infection with Borrelia spirochetes through a highly orchestrated immune defense involving innate and adaptive effector functions aimed toward limiting pathogen burdens, minimizing tissue injury, and preventing subsequent reinfection. The evolutionary adaptation of Borrelia spirochetes to their reservoir mammalian hosts may allow for its persistence despite this immune defense. This review summarizes our current understanding of the host immune response to B. burgdorferi sensu lato, the most widely studied Borrelia spp. and etiologic agent of Lyme borreliosis. Pertinent literature will be reviewed with emphasis on in vitro, ex vivo and animal studies that influenced our understanding of both the earliest responses to B. burgdorferi as it enters the mammalian host and those that evolve as spirochetes disseminate and establish infection in multiple tissues. Our focus is on the immune response of inbred mice, the most commonly studied animal model of B. burgdorferi infection and surrogate for one of this pathogen's principle natural reservoir hosts, the white-footed deer mouse. Comparison will be made to the immune responses of humans with Lyme borreliosis. Our goal is to provide an understanding of the dynamics of the mammalian immune response during infection with B. burgdorferi and its relation to the outcomes in reservoir (mouse) and non-reservoir (human) hosts.

Freeman P. Efficacy of Double-Dose Dapsone Combination Therapy in the Treatment of Chronic Lyme Disease/Post-Treatment Lyme Disease Syndrome (PTLDS) and Associated Co-infections: A Report of Three Cases and Retrospective Chart Review

Three patients with multi-year histories of relapsing and remitting Lyme disease and associated co-infections despite extended antibiotic therapy were each given double-dose dapsone combination therapy (DDD CT) for a total of 7-8 weeks. At the completion of therapy, all three patients' major Lyme symptoms remained in remission for a period of 25-30 months. A retrospective chart review of 37 additional patients undergoing DDD CT therapy (40 patients in total) was also performed, which demonstrated tick-borne symptom improvements in 98% of patients, with 45% remaining in remission for 1 year or longer. In conclusion, double-dose dapsone therapy could represent a novel and effective anti-infective strategy in chronic Lyme disease/ post-treatment Lyme disease syndrome (PTLDS), especially in those individuals who have failed regular dose dapsone combination therapy (DDS CT) or standard antibiotic protocols. A randomized, blinded, placebo-controlled trial is warranted to evaluate the efficacy of DDD CT in those individuals with chronic Lyme disease/PTLDS.

IL-12 Blocks Tfh Cell Differentiation during Salmonella Infection, thereby Contributing to Germinal Center Suppression

Germinal centers (GC) are crucial for the formation of long-lived humoral immunity. Many pathogens suppress GC, including Salmonella enterica serovar Typhimurium (STm), but the mechanisms driving suppression remain unknown. We report that neither plasmablasts nor STm-specific B cells are required for GC suppression in mice. Rather, we identify that interleukin-12 (IL-12), but not interferon-γ (IFN-γ), directly suppresses T follicular helper (Tfh) cell differentiation of T cells intrinsically. Administering recombinant IL-12 during nitrophenyl-Chicken Gamma Globulin (NP-CGG) immunization also suppresses Tfh cell differentiation and GC B cells, indicating that IL-12 is sufficient to suppress Tfh cell differentiation independent of STm infection. Recombinant IL-12 induces high levels of T-bet, and T-bet is necessary for Tfh cell suppression. Therefore, IL-12 induced during STm infection in mice contributes to GC suppression via suppression of Tfh cell differentiation. More broadly, these data suggest that IL-12 can tailor the proportions of humoral (Tfh cell) and cellular (T helper type 1 [Th1] cell) immunity to the infection, with implications for IL-12 targeting therapies in autoimmunity and vaccination.

Proteomic as an Exploratory Approach to Develop Vaccines Against Tick-Borne Diseases Using Lyme Borreliosis as a Test Case

Tick-borne diseases affecting humans and animals are on the rise worldwide. Vaccines constitute an effective control measure, but very few are available. We selected Lyme borreliosis, a bacterial infection transmitted by the hard tick Ixodes, to validate a new concept to identify vaccine candidates. This disease is the most common tick-borne disease in the Northern Hemisphere. Although attempts to develop a vaccine exist, none have been successfully marketed. In tick-borne diseases, the skin constitutes a very specific environment encountered by the pathogen during its co-inoculation with tick saliva. In a mouse model, we developed a proteomic approach to identify vaccine candidates in skin biopsies. We identified 30 bacterial proteins after syringe inoculation or tick inoculation of bacteria. Discovery proteomics using mass spectrometry might be used in various tick-borne diseases to identify pathogen proteins with early skin expression. It should help to better develop sub-unit vaccines based on a cocktail of several antigens, associated with effective adjuvant and delivery systems of antigens. In all vector-borne diseases, the skin deserves further investigation to better define its role in the elaboration of protective immunity against pathogens.

Deciphering SARS-CoV-2 Virologic and Immunologic Features

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 and its associated pathology, COVID-19, have been of particular concerns these last months due to the worldwide burden they represent. The number of cases requiring intensive care being the critical point in this epidemic, a better understanding of the pathophysiology leading to these severe cases is urgently needed. Tissue lesions can be caused by the pathogen or can be driven by an overwhelmed immune response. Focusing on SARS-CoV-2, we and others have observed that this virus can trigger indeed an immune response that can be dysregulated in severe patients and leading to further injury to multiple organs. The purpose of the review is to bring to light the current knowledge about SARS-CoV-2 virologic and immunologic features. Thus, we address virus biology, life cycle, tropism for many organs and how ultimately it will affect several host biological and physiological functions, notably the immune response. Given that therapeutic avenues are now highly warranted, we also discuss the immunotherapies available to manage the infection and the clinical outcomes.

A Clinical Diagnostic System for Late-Stage Neuropsychiatric Lyme Borreliosis Based upon an Analysis of 100 Patients

Many late-stage chronic Lyme disease clinical findings are neuropsychiatric. A total clinical assessment is critical in diagnosis, especially since controversy surrounds the reliability of laboratory testing. The clinical findings of one hundred Lyme disease patients with chronic neuropsychiatric symptoms were entered into a database. The prevalence of each clinical finding pre-infection and post-infection was compared and calculated within the 95% confidence interval. Patients had minimal symptoms pre-infection, but a high post-infection prevalence of a broad spectrum of acquired multisystem symptoms. These findings included impairments of attention span, memory, processing, executive functioning, emotional functioning, behavior, psychiatric syndromes, vegetative functioning, neurological, musculoskeletal, cardiovascular, upper respiratory, dental, pulmonary, gastrointestinal, genitourinary, and other symptoms. The most prevalent symptoms included sustained attention impairments, brain fog, unfocused concentration, joint symptoms, distraction by frustration, depression, working memory impairments, decreased school/job performance, recent memory impairments, difficulty prioritizing multiple tasks, fatigue, non-restorative sleep, multitasking difficulties, sudden mood swings, hypersomnia, mental apathy, decreased social functioning, insomnia, tingling, word finding difficulties, name retrieval, headaches, sound hypersensitivity, paresis, anhedonia, depersonalization, cold intolerance, body temperature fluctuations, light sensitivity and dysfluent speech. The average patient had five symptoms pre-infection and 82 post-infection. Pattern recognition is critical in making a diagnosis. This study was used to develop three clinical assessment forms.

Lyme Disease Frontiers: Reconciling Borrelia Biology and Clinical Conundrums

Lyme disease is a complex tick-borne zoonosis that poses an escalating public health threat in several parts of the world, despite sophisticated healthcare infrastructure and decades of effort to address the problem. Concepts like the true burden of the illness, from incidence rates to longstanding consequences of infection, and optimal case management, also remain shrouded in controversy. At the heart of this multidisciplinary issue are the causative spirochetal pathogens belonging to the Borrelia Lyme complex. Their unusual physiology and versatile lifestyle have challenged microbiologists, and may also hold the key to unlocking mysteries of the disease. The goal of this review is therefore to integrate established and emerging concepts of Borrelia biology and pathogenesis, and position them in the broader context of biomedical research and clinical practice. We begin by considering the conventions around diagnosing and characterizing Lyme disease that have served as a conceptual framework for the discipline. We then explore virulence from the perspective of both host (genetic and environmental predispositions) and pathogen (serotypes, dissemination, and immune modulation), as well as considering antimicrobial strategies (lab methodology, resistance, persistence, and clinical application), and borrelial adaptations of hypothesized medical significance (phenotypic plasticity or pleomorphy).

Complement Evasion in Borrelia spirochetes: Mechanisms and Opportunities for Intervention

Lyme disease (LD) is an increasingly prevalent, climate change-accelerated, vector-borne infectious disease with significant morbidity and cost in a proportion of patients who experience ongoing symptoms after antibiotic treatment, a condition known as post-treatment Lyme disease syndrome (PTLDS). Spirochetal bacteria of Borrelia species are the causative agents of LD. These obligate parasites have evolved sophisticated immune evasion mechanisms, including the ability to defeat the innate immune system’s complement cascade. Research on complement function and Borrelia evasion mechanisms, focusing on human disease, is reviewed, highlighting opportunities to build on existing knowledge. Implications for the development of new antibiotic therapies having the potential to prevent or cure PTLDS are discussed. It is noted that a therapy enabling the complement system to effectively counter Borrelia might have lower cost and fewer side-effects and risks than broad-spectrum antibiotic use and could avert the need to develop and administer a vaccine.

Disulfiram (Tetraethylthiuram Disulfide) in the Treatment of Lyme Disease and Babesiosis: Report of Experience in Three Cases

Three patients, each of whom had required intensive open-ended antimicrobial therapy for control of the symptoms of chronic relapsing neurological Lyme disease and relapsing babesiosis, were able to discontinue treatment and remain clinically well for periods of observation of 6–23 months following the completion of a finite course of treatment solely with disulfiram. One patient relapsed at six months and is being re-treated with disulfiram.