Immune complexes and late complement proteins trigger activation of Syk tyrosine kinase in human CD4(+) T cells

Assessment of the role of high-density lipoproteins and their immunomodulatory activity in systemic lupus erythematosus immunopathology

OBJECTIVE

To explore the potential associations between high-density lipoprotein (HDL) levels and inflammasome components in the context of systemic lupus erythematosus (SLE).

METHODS

A cross-sectional study was conducted. A group of 50 patients with SLE and 50 healthy controls matched by sex and similar age ranges were enrolled. Serum HDL cholesterol (HDL-C) and C reactive protein (CRP) levels were quantified. Serum cytokine levels, including IL-1β and IL-6, were determined by ELISA. The gene expression of inflammasome-related genes in peripheral blood mononuclear cells was measured by quantitative real-time PCR.

RESULTS

HDL-C levels were lower in the patients with SLE (p<0.05), and on segregation according to disease activity, those with active SLE had the lowest HDL-C levels. Patients with SLE presented higher concentrations of the serum inflammatory cytokines IL-1β and IL-6 (p<0.0001) but similar levels of CRP to those in controls. A similar scenario was observed for the gene expression of inflammasome components, where all the evaluated markers were significantly upregulated in the SLE population. These results revealed significant negative correlations between HDL levels and disease activity, serum IL-6 and IL-1β levels and the mRNA expression of NLRP3, IL-1β and IL-18. In addition, significant positive correlations were found between disease activity and serum IL-1β and between disease activity and the mRNA expression of IL-18, and interestingly, significant positive correlations were also observed between active SLE and serum IL-1β and the mRNA expression of NLRP3.

CONCLUSION

Our results suggest that HDL is essential for SLE beyond atherosclerosis and is related to inflammation regulation, possibly mediated by inflammasome immunomodulation.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Post-translational modifications in T cells in systemic erythematosus lupus

Systemic erythematosus lupus (SLE) is a classic autoimmune disease characterized by multiple autoantibodies and immune-mediated tissue damage. The aetiology of this disease is still unclear. A new drug, belimumab, which acts against the B-lymphocyte stimulator (BLyS), can effectively improve the condition of SLE patients, but it cannot resolve all SLE symptoms. The discovery of novel, precise therapeutic targets is urgently needed. It is well known that abnormal T-cell function is one of the most crucial factors contributing to the pathogenesis of SLE. Protein post-translational modifications (PTMs), including phosphorylation, glycosylation, acetylation, methylation, ubiquitination and SUMOylation have been emphasized for their roles in activating protein activity, maintaining structural stability, regulating protein-protein interactions and mediating signalling pathways, in addition to other biological functions. Summarizing the latest data in this area, this review focuses on the potential roles of diverse PTMs in regulating T-cell function and signalling pathways in SLE pathogenesis, with the goal of identifying new targets for SLE therapy.

Complement activation and increased expression of Syk, mucin-1 and CaMK4 in kidneys of patients with COVID-19

Acute and chronic kidney failure is common in hospitalized patients with COVID-19, yet the mechanism of injury and predisposing factors remain poorly understood. We investigated the role of complement activation by determining the levels of deposited complement components (C1q, C3, FH, C5b-9) and immunoglobulin along with the expression levels of the injury-associated molecules spleen tyrosine kinase (Syk), mucin-1 (MUC1) and calcium/calmodulin-dependent protein kinase IV (CaMK4) in the kidney tissues of people who succumbed to COVID-19. We report increased deposition of C1q, C3, C5b-9, total immunoglobulin, and high expression levels of Syk, MUC1 and CaMK4 in the kidneys of COVID-19 patients. Our study provides strong rationale for the expansion of trials involving the use of inhibitors of these molecules, in particular C1q, C3, Syk, MUC1 and CaMK4 to treat patients with COVID-19.

Characterization of the mechanism of action of lanraplenib, a novel spleen tyrosine kinase inhibitor, in models of lupus nephritis

Background

B cells are critical mediators of systemic lupus erythematosus (SLE) and lupus nephritis (LN), and antinuclear antibodies can be found in the serum of approximately 98% of patients with SLE. Spleen tyrosine kinase (SYK) is a nonreceptor tyrosine kinase that mediates signaling from immunoreceptors, including the B cell receptor. Active, phosphorylated SYK has been observed in tissues from patients with SLE or cutaneous lupus erythematosus, and its inhibition is hypothesized to ameliorate disease pathogenesis. We sought to evaluate the efficacy and characterize the mechanism of action of lanraplenib, a selective oral SYK inhibitor, in the New Zealand black/white (NZB/W) murine model of SLE and LN.

Methods

Lanraplenib was evaluated for inhibition of primary human B cell functions in vitro. Furthermore, the effect of SYK inhibition on ameliorating LN-like disease in vivo was determined by treating NZB/W mice with lanraplenib, cyclophosphamide, or a vehicle control. Glomerulopathy and immunoglobulin G (IgG) deposition were quantified in kidneys. The concentration of proinflammatory cytokines was measured in serum. Splenocytes were analyzed by flow cytometry for B cell maturation and T cell memory maturation, and the presence of T follicular helper and dendritic cells.

Results

In human B cells in vitro, lanraplenib inhibited B cell activating factor-mediated survival as well as activation, maturation, and immunoglobulin M production. Treatment of NZB/W mice with lanraplenib improved overall survival, prevented the development of proteinuria, and reduced blood urea nitrogen concentrations. Kidney morphology was significantly preserved by treatment with lanraplenib as measured by glomerular diameter, protein cast severity, interstitial inflammation, vasculitis, and frequency of glomerular crescents; treatment with lanraplenib reduced glomerular IgG deposition. Mice treated with lanraplenib had reduced concentrations of serum proinflammatory cytokines. Lanraplenib blocked disease-driven B cell maturation and T cell memory maturation in the spleen.

Conclusions

Lanraplenib blocked the progression of LN-like disease in NZB/W mice. Human in vitro and murine in vivo data suggest that lanraplenib may be efficacious in preventing disease progression in patients with LN at least in part by inhibiting B cell maturation. These data provide additional rationale for the use of lanraplenib in the treatment of SLE and LN.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41927-021-00178-3.

Complement Membrane Attack Complex: New Roles, Mechanisms of Action, and Therapeutic Targets

The complement membrane attack complex (MAC) is classically known as a cytolytic effector of innate and adaptive immunity that forms pores in the plasma membrane of pathogens or targeted cells, leading to osmolysis. Nucleated cells resist MAC-mediated cytolysis by expression of inhibitors that block MAC assembly or by rapid removal of MAC through endocytosis or shedding. In the absence of lysis, MAC may induce intracellular signaling and cell activation, responses implicated in a variety of autoimmune, inflammatory, and transplant disease settings. New discoveries into the structure and biophysical properties of MAC revealed heterogeneous MAC precursors and conformations that provide insights into MAC function. In addition, new mechanisms of MAC-mediated signaling and its contribution to disease pathogenesis have recently come to light. MAC-activated cells have been found to express proinflammatory proteins-often through NF-κB-dependent transcription, assemble inflammasomes, enabling processing, and facilitate secretion of IL-1β and IL-18, as well as other signaling pathways. These recent insights into the mechanisms of action of MAC provide an updated framework to therapeutic approaches that can target MAC assembly, signaling, and proinflammatory effects in various complement-mediated diseases.

Complement After Trauma: Suturing Innate and Adaptive Immunity

The overpowering effect of trauma on the immune system is undisputed. Severe trauma is characterized by systemic cytokine generation, activation and dysregulation of systemic inflammatory response complementopathy and coagulopathy, has been immensely instrumental in understanding the underlying mechanisms of the innate immune system during systemic inflammation. The compartmentalized functions of the innate and adaptive immune systems are being gradually recognized as an overlapping, interactive and dynamic system of responsive elements. Nonetheless the current knowledge of the complement cascade and its interaction with adaptive immune response mediators and cells, including T- and B-cells, is limited. In this review, we discuss what is known about the bridging effects of the complement system on the adaptive immune system and which unexplored areas could be crucial in understanding how the complement and adaptive immune systems interact following trauma.

siRNA Library Screening Identifies a Druggable Immune-Signature Driving Esophageal Adenocarcinoma Cell Growth

BACKGROUND & AIMS

Effective therapeutic approaches are urgently required to tackle the alarmingly poor survival outcomes in esophageal adenocarcinoma (EAC) patients. EAC originates from within the intestinal-type metaplasia, Barrett's esophagus, a condition arising on a background of gastroesophageal reflux disease and associated inflammation.

METHODS

This study used a druggable genome small interfering RNA (siRNA) screening library of 6022 siRNAs in conjunction with bioinformatics platforms, genomic studies of EAC tissues, somatic variation data of EAC from The Cancer Genome Atlas data of EAC, and pathologic and functional studies to define novel EAC-associated, and targetable, immune factors.

RESULTS

By using a druggable genome library we defined genes that sustain EAC cell growth, which included an unexpected immunologic signature. Integrating Cancer Genome Atlas data with druggable siRNA targets showed a striking concordance and an EAC-specific gene amplification event associated with 7 druggable targets co-encoded at Chr6p21.1. Over-representation of immune pathway-associated genes supporting EAC cell growth included leukemia inhibitory factor, complement component 1, q subcomponent A chain (C1QA), and triggering receptor expressed on myeloid cells 2 (TREM2), which were validated further as targets sharing downstream signaling pathways through genomic and pathologic studies. Finally, targeting the triggering receptor expressed on myeloid cells 2-, C1q-, and leukemia inhibitory factor-activated signaling pathways (TYROBP-spleen tyrosine kinase and JAK-STAT3) with spleen tyrosine kinase and Janus-activated kinase inhibitor fostamatinib R788 triggered EAC cell death, growth arrest, and reduced tumor burden in NOD scid gamma mice.

CONCLUSIONS

These data highlight a subset of genes co-identified through siRNA targeting and genomic studies of expression and somatic variation, specifically highlighting the contribution that immune-related factors play in support of EAC development and suggesting their suitability as targets in the treatment of EAC.

FcγRIIIa Signaling Modulates Endosomal TLR Responses in Human CD4+ T Cells

Recognition of Ab-opsonized pathogens by immune cells triggers both TLR and Fc receptor signaling. Fc receptors endocytose modified nucleic acids bound to Abs and deliver them to endosomes, where they are recognized by nucleic acid-sensing TLRs (NA-TLRs). We show that in CD4+ T cells, NA-TLRs, TLR3, TLR8, and TLR9 are upregulated by FcγRIIIa-pSyk cosignaling and localize with FcγRIIIa on the cell surface. TLR9 accumulates on the cell surface, where it recognizes CpG oligonucleotide 2006. Subcellular location of NA-TLRs is a key determinant in discriminating self versus viral nucleic acid. Hydroxychloroquine used for treating systemic lupus erythematosus and a Syk inhibitor blocked NA-TLR localization with FcγRIIIa. Engaging TLR9 with CpG oligonucleotide contributes to the development of IL17A+ and IL-21+ populations. RNA-sequencing analysis showed upregulation of proinflammatory cytokines, NF-κB signaling, and heat shock protein pathway RNA transcripts. These data suggest a role for FcγRIIIa-pSyk cosignaling in modulating NA-TLR responses in human CD4+ T cells by affecting the amounts and cellular distribution. These events are important for understanding of autoimmune pathology.

Promising Role of Toll-Like Receptor 8 Agonist in Concert with Prostratin for Activation of Silent HIV

The persistence of latently HIV-infected cells in patients under combined antiretroviral treatment (cART) remains the major hurdle for HIV eradication. Thus far, individual compounds have not been sufficiently potent to reactivate latent virus and guarantee its elimination in vivo. Thus, we hypothesized that transcriptional enhancers, in concert with compounds triggering the innate immune system, are more efficient in reversing latency by creating a Th1 supportive milieu that acts against latently HIV-infected cells at various levels. To test our hypothesis, we screened six compounds on a coculture of latently infected cells (J-lat) and monocyte-derived dendritic cells (MDDCs). The protein kinase C (PKC) agonist prostratin, with a Toll-like receptor 8 (TLR8) agonist, resulted in greater reversion of HIV latency than any single compound. This combinatorial approach led to a drastic phenotypic and functional maturation of the MDDCs. Tumor necrosis factor (TNF) and cell-cell interactions were crucial for the greater reversion observed. Similarly, we found a greater potency of the combination of prostratin and TLR8 agonist in reversing HIV latency when applying it to primary cells of HIV-infected patients. Thus, we demonstrate here the synergistic interplay between TLR8-matured MDDCs and compounds acting directly on latently HIV-infected cells, targeting different mechanisms of latency, by triggering various signaling pathways. Moreover, TLR8 triggering may reverse exhaustion of HIV-specific cytotoxic T lymphocytes that might be essential for killing or constraining the latently infected cells.

IMPORTANCE

Curing HIV is the Holy Grail. The so-called "shock and kill" strategy relies on drug-mediated reversion of HIV latency and the subsequent death of those cells under combined antiretroviral treatment. So far, no compound achieves efficient reversal of latency or eliminates this latent reservoir. The compounds may not target all of the latency mechanisms in all latently infected cells. Moreover, HIV-associated exhaustion of the immune system hinders the efficient elimination of the reactivated cells. In this study, we demonstrated synergistic latency reversion by combining agonists for protein kinase C and Toll-like receptor 8 in a coculture of latently infected cells with myeloid dendritic cells. The drug prostratin stimulates directly the transcriptional machinery of latently infected cells, and the TLR8 agonist acts indirectly by maturing dendritic cells. These findings highlight the importance of the immune system and its activation, in combination with direct-acting compounds, to reverse latency.

Human CD4(+) T-Cells: A Role for Low-Affinity Fc Receptors

Both lymphoid and myeloid cells express Fc receptors (FcRs). Low-affinity FcRs engage circulating immune complexes, which results in the cellular activation and pro-inflammatory cytokine production. FcRs participate in the internalization, transport, and/or recycling of antibodies and antigens. Cytosolic FcRs also route these proteins to proteasomes and antigen-presentation pathways. Non-activated CD4(+) T-cells do not express FcRs. Once activated, naive CD4(+) T-cells express FcγRIIIa, which, upon IC ligation, provide a costimulatory signal for the differentiation of these cells into effector cell population. FcγRIIIa present on CD4(+) T-cell membrane could internalize nucleic acid-containing ICs and elicit a cross-talk with toll-like receptors. FcγRIIIa common γ-chain forms a heterodimer with the ζ-chain of T-cell receptor complex, suggesting a synergistic role for these receptors. This review first summarizes our current understanding of FcRs on CD4(+) T-cells. Thereafter, I will attempt to correlate the findings from the recent literature on FcRs and propose a role for these receptors in modulating adaptive immune responses via TLR signaling, nucleic acid sensing, and epigenetic changes in CD4(+) T-cells.

Immunogenicity to Biotherapeutics - The Role of Anti-drug Immune Complexes

Biological molecules are increasingly becoming a part of the therapeutics portfolio that has been either recently approved for marketing or those that are in the pipeline of several biotech and pharmaceutical companies. This is largely based on their ability to be highly specific relative to small molecules. However, by virtue of being a large protein, and having a complex structure with structural variability arising from production using recombinant gene technology in cell lines, such therapeutics run the risk of being recognized as foreign by a host immune system. In the context of immune-mediated adverse effects that have been documented to biological drugs thus far, including infusion reactions, and the evolving therapeutic platforms in the pipeline that engineer different functional modules in a biotherapeutic, it is critical to understand the interplay of the adaptive and innate immune responses, the pathophysiology of immunogenicity to biological drugs in instances where there have been immune-mediated adverse clinical sequelae and address technical approaches for their laboratory evaluation. The current paradigm in immunogenicity evaluation has a tiered approach to the detection and characterization of anti-drug antibodies (ADAs) elicited in vivo to a biotherapeutic; alongside with the structural, biophysical, and molecular information of the therapeutic, these analytical assessments form the core of the immunogenicity risk assessment. However, many of the immune-mediated adverse effects attributed to ADAs require the formation of a drug/ADA immune complex (IC) intermediate that can have a variety of downstream effects. This review will focus on the activation of potential immunopathological pathways arising as a consequence of circulating as well as cell surface bound drug bearing ICs, risk factors that are intrinsic either to the therapeutic molecule or to the host that might predispose to IC-mediated effects, and review the recent literature on prevalence and intensity of established examples of type II and III hypersensitivity reactions that follow the administration of a biotherapeutic. Additionally, we propose methods for the study of immune parameters specific to the biology of ICs that could be of use in conjunction with the detection of ADAs in circulation.

FcγRIIIa-Syk Co-signal Modulates CD4+ T-cell Response and Up-regulates Toll-like Receptor (TLR) Expression

CD4(+) T-cells in systemic lupus erythematosus (SLE) patients show altered T-cell receptor signaling, which utilizes Fc-receptor γ-chain FcRγ-Syk. A role for FcγRIIIa activation from immune complex (IC) ligation and sublytic terminal complement complex (C5b-9) in CD4(+) T-cell responses is not investigated. In this study, we show that the ICs present in SLE patients by ligating to FcγRIIIa on CD4(+) T-cells phosphorylate Syk and provide a co-stimulatory signal to CD4(+) T-cells in the absence of CD28 signal. This led to the development of pathogenic IL-17A(+) and IFN-γ(high) CD4(+) T-cells in vitro. Cytokines IL-1β, IL-6, TGF-β1, and IL-23 were the only requirement for the development of both populations. SLE patients CD4(+) T-cells that expressed CD25, CD69, and CD98 bound to ICs showed pSyk and produced IFN-γ and IL-17A. This FcγRIIIa-mediated co-signal differentially up-regulated the expression of IFN pathway genes compared with CD28 co-signal. FcγRIIIa-pSyk up-regulated several toll-like receptor genes as well as the HMGB1 and MyD88 gene transcripts. ICs co-localized with these toll-like receptor pathway proteins. These results suggest a role for the FcγRIIIa-pSyk signal in modulating adaptive immune responses.

Induced expression of FcγRIIIa (CD16a) on CD4+ T cells triggers generation of IFN-γhigh subset

Whether or not CD4(+) T-cells express low affinity receptor FcγRIIIa (CD16a) in disease pathology has not been examined in great detail. In this study, we show that a subset of activated CD4(+) T-cells in humans express FcγRIIIa. The ligation of FcγRIIIa by immune complexes (ICs) in human CD4(+) T-cells produced co-stimulatory signal like CD28 that triggered IFN-γ production. The induced expression of FcγRIIIa on CD4(+) helper T-cells is an important finding since these receptors via ITAM contribute to intracellular signaling. The induced expression of FcγRIIIa on CD4(+) T helper cells and their ability to co-stimulate T-cell activation are important and novel findings that may reveal new pathways to regulate adaptive immune responses during inflammation and in autoimmunity.

The complement system in systemic lupus erythematosus: an update

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

T cell receptor-associated protein tyrosine kinases: the dynamics of tolerance regulation by phosphorylation and its role in systemic lupus erythematosus

There are different abnormalities that lead to the autoreactive phenotype in T cells from systemic lupus erythematosus (SLE) patients. Proximal signaling, involving the T-cell receptor (TCR) and its associated protein tyrosine kinases (PTKs), is significantly affected in SLE. This ultimately leads to aberrant responses, which include enhanced tyrosine phosphorylation and calcium release, as well as decreased IL-2 secretion. Lck, ZAP70 and Syk, which are PTKs with a major role in proximal signaling, all present abnormal functioning that contributes to an altered T cell response in these patients. A number of other molecules, especially regulatory proteins, are also involved. This review will focus on the PTKs that participate in proximal signaling, with specific emphasis on their relevance in maintaining peripheral tolerance, their abnormalities in SLE and how these contribute to an altered T cell response.

Targeting the SYK-BTK axis for the treatment of immunological and hematological disorders: recent progress and therapeutic perspectives

Spleen Tyrosine Kinase (SYK) and Bruton's Tyrosine Kinase (BTK) are non-receptor cytoplasmic tyrosine kinases that are primarily expressed in cells of hematopoietic lineage. Both are key mediators in coupling activated immunoreceptors to downstream signaling events that affect diverse biological functions, from cellular proliferation, differentiation and adhesion to innate and adaptive immune responses. As such, pharmacological inhibitors of SYK or BTK are being actively pursued as potential immunomodulatory agents for the treatment of autoimmune and inflammatory disorders. Deregulation of SYK or BTK activity has also been implicated in certain hematological malignancies. To date, from a clinical perspective, pharmacological inhibition of SYK activity has demonstrated encouraging efficacy in patients with rheumatoid arthritis (RA), while patients with relapsed or refractory chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) have benefited from covalent inhibitors of BTK in early clinical studies. Here, we review and discuss recent insights into the emerging role of the SYK-BTK axis in innate immune cell function as well as in the maintenance of survival and homing signals for tumor cell progression. The current progress on the clinical development of SYK and BTK inhibitors is also highlighted.

Molecular basis for T cell response induced by altered peptide ligand of type II collagen

Mounting evidence from animal models has demonstrated that alterations in peptide-MHC interactions with the T cell receptor (TCR) can lead to dramatically different T cell outcomes. We have developed an altered peptide ligand of type II collagen, referred to as A9, which differentially regulates TCR signaling in murine T cells leading to suppression of arthritis in the experimental model of collagen-induced arthritis. This study delineates the T cell signaling pathway used by T cells stimulated by the A9·I-A(q) complex. We have found that T cells activated by A9 bypass the requirement for Zap-70 and CD3-ζ and signal via FcRγ and Syk. Using collagen-specific T cell hybridomas engineered to overexpress either Syk, Zap-70, TCR-FcRγ, or CD3-ζ, we demonstrate that A9·I-A(q) preferentially activates FcRγ/Syk but not CD3-ζ/Zap-70. Moreover, a genetic absence of Syk or FcRγ significantly reduces the altered peptide ligand induction of the nuclear factor GATA3. By dissecting the molecular mechanism of A9-induced T cell signaling we have defined a new alternate pathway that is dependent upon FcRγ and Syk to secrete immunoregulatory cytokines. Given the interest in using Syk inhibitors to treat patients with rheumatoid arthritis, understanding this pathway may be critical for the proper application of this therapy.