Immunostimulatory flagellin from Burkholderia pseudomallei effects on an increase in the intracellular calcium concentration and up-regulation of TNF-alpha by mononuclear cells

A bibliometric analysis: Ca2+ fluxes and inflammatory phenotyping by flow cytometry in peripheral blood mononuclear cells

Background

The immune system, composed of organs, tissues, cells, and proteins, is the key to protecting the body from external biological attacks and inflammation. The latter occurs in several pathologies, such as cancers, type 1 diabetes, and human immunodeficiency virus infection. Immunophenotyping by flow cytometry is the method of choice for diagnosing these pathologies. Under inflammatory conditions, the peripheral blood mononuclear cells (PBMCs) are partially activated and generate intracellular pathways involving Ca2+-dependent signaling cascades leading to transcription factor expression. Ca2+ signaling is typically studied by microscopy in cell lines but can present some limitations to explore human PBMCs, where flow cytometry can be a good alternative.

Objective

In this review, we dived into the research field of inflammation and Ca2+ signaling in PBMCs. We aimed to investigate the structure and evolution of this field in a physio-pathological context, and then we focused our review on flow cytometry analysis of Ca2+ fluxes in PBMCs.

Methods

From 1984 to 2022, 3865 articles on inflammation and Ca2+ signaling in PBMCs were published, according to The Clarivate Web of Science (WOS) database used in this review. A bibliometric study was designed for this collection and consisted of a co-citation and bibliographic coupling analysis.

Results

The co-citation analysis was performed on 133 articles: 4 clusters highlighted the global context of Ca2+ homeostasis, including chemical probe development, identification of the leading players in Ca2+ signaling, and the link with chemokine production in immune cell function. Next, the bibliographic coupling analysis combined 998 articles in 8 clusters. This analysis outlined the mechanisms of PBMC activation, from signal integration to cellular response. Further explorations of the bibliographic coupling network, focusing on flow cytometry, revealed 21 articles measuring cytosolic Ca2+ in PBMCs, with only 5 since 2016. This final query showed that Ca2+ signaling analysis in human PBMCs using flow cytometry is still underdeveloped and investigates mainly the cytosolic Ca2+ compartment.

Conclusion

Our review uncovers remaining knowledge gaps of intracellular players involved in Ca2+ signaling in PBMCs, such as reticulum and mitochondria, and presents flow cytometry as a solid option to supplement gold-standard microscopy studies.

Enterobacter cloacae: a villain in CaOx stone disease?

To explore the roles microbiome of urinary tract played in calcium oxalate stones (CaOx) formation, we collected two sides’ pelvis urine of patients with unilateral CaOx stones to set self-control to diminish the influence of systemic factors. Patients with unilateral CaOx stones were recruited in our study according to strict criteria. 16S rRNA gene sequencing was applied to every pair of pelvis urine. Bacterial genome sequencing of Enterobacter cloacae was conducted and bioinformatic analysis was applied to explore the possible pathways of Enterobacter cloacae inducing CaOx stones formation. In vivo experiments were conducted to validate our claims. Von Kossa staining, TUNEL assay and Western Blot were applied to SD rats exploring the mechanism of stone formation. We found 26 significantly different bacteria between stone sides and non-stone sides’ pelvis urine, among which Enterobacter cloacae ranked the most different. Bacterial genome sequencing of Enterobacter cloacae revealed that its virulence factors included Flagellin, LPS and Fimbrial. GO and KEGG analysis revealed it probably induced CaOx stone formation via ion binging and signaling transduction pathways. The results of animal experiments indicated that Glyoxylic Acid could promote apoptosis and crystal depositions of kidney comparing with control group while pre-injected with Enterobacter cloacae could apparently compound the effects. While Western Blot demonstrated that Glyoxylic Acid or Enterobacter cloacae could increase the expression of IL-6, Mcp-1, BMP2 and OPN in rats’ kidney, Glyoxylic Acid and Enterobacter cloacae together could aggravate these increases. These findings indicated that Enterobacter cloacae might play important roles in CaOx stones formation. However, this study is just a preliminary exploration; further studies still need to be conducted.

An Evolutionary Arms Race Between Burkholderia pseudomallei and Host Immune System: What Do We Know?

A better understanding of co-evolution between pathogens and hosts holds promise for better prevention and control strategies. This review will explore the interactions between Burkholderia pseudomallei, an environmental and opportunistic pathogen, and the human host immune system. B. pseudomallei causes "Melioidosis," a rapidly fatal tropical infectious disease predicted to affect 165,000 cases annually worldwide, of which 89,000 are fatal. Genetic heterogeneities were reported in both B. pseudomallei and human host population, some of which may, at least in part, contribute to inter-individual differences in disease susceptibility. Here, we review (i) a multi-host-pathogen characteristic of the interaction; (ii) selection pressures acting on B. pseudomallei and human genomes with the former being driven by bacterial adaptation across ranges of ecological niches while the latter are driven by human encounter of broad ranges of pathogens; (iii) the mechanisms that generate genetic diversity in bacterial and host population particularly in sequences encoding proteins functioning in host-pathogen interaction; (iv) reported genetic and structural variations of proteins or molecules observed in B. pseudomallei-human host interactions and their implications in infection outcomes. Together, these predict bacterial and host evolutionary trajectory which continues to generate genetic diversity in bacterium and operates host immune selection at the molecular level.

Role of Toll-Like Receptor 5 (TLR5) in Experimental Melioidosis

The Gram-negative intracellular pathogen Burkholderia pseudomallei is the causative agent of melioidosis, an important cause of sepsis in Southeast Asia. Recognition of pathogen-associated molecular patterns by Toll-like receptors (TLRs) is essential for an appropriate immune response during pathogen invasion. In patients with melioidosis, TLR5 is the most abundantly expressed TLR, and a hypofunctional TLR5 variant has been associated with improved survival. Here, we studied the functional role of TLR5 and its ligand flagellin in experimental melioidosis. First, we observed differential TLR5 expression in the pulmonary and hepatic compartments upon infection with B. pseudomallei Next, we found that B. pseudomallei-challenged TLR5-deficient (Tlr5^-/- ) mice were more susceptible to infection than wild-type (WT) mice, as demonstrated by higher systemic bacterial loads, increased organ injury, and impaired survival. Lung bacterial loads were not different between the two groups. The phenotype was flagellin independent; no difference in in vivo virulence was observed for the flagellin-lacking mutant MM36 compared to the wild-type B. pseudomallei strain 1026b. Tlr5^-/- mice showed a similar impaired antibacterial defense when infected with MM36 or 1026b. Ex vivo experiments showed that TLR5-deficient macrophages display markedly impaired phagocytosis of B. pseudomallei In conclusion, these data suggest that TLR5 deficiency has a detrimental flagellin-independent effect on the host response against pulmonary B. pseudomallei infection.

Inhibition of calmodulin increases intracellular survival of Salmonella in chicken macrophage cells

Calcium (Ca²⁺) is a pivotal intracellular second messenger and calmodulin (CaM) acts as a multifunctional Ca²⁺-binding protein that regulates downstream Ca²⁺ dependent signaling. Together they play an important role in regulating various cellular functions, including gene expression, maturation of phagolysosome, apoptosis, and immune response. Intracellular Ca²⁺ has been shown to play a critical role in Toll-like receptor-mediated immune response to microbial agonists in the HD11 chicken macrophage cell line. The role of that the Ca²⁺/CaM pathway plays in the intracellular survival of Salmonella in chicken macrophages has not been reported. In this study, kinome peptide array analysis indicated that the Ca²⁺/CaM pathway was significantly activated when chicken macrophage HD11 cells were infected with S. Enteritidis or S. Heidelberg. Further study demonstrated that treating cells with a pharmaceutical CaM inhibitor W-7, which disrupts the formation of Ca²⁺/CaM, significantly inhibited macrophages to produce nitric oxide and weaken the control of intracellular Salmonella replication. These results strongly indicate that CaM plays an important role in the innate immune response of chicken macrophages and that the Ca²⁺/CaM mediated signaling pathway is critically involved in the host cell response to Salmonella infection.

MDCO-216 Does Not Induce Adverse Immunostimulation, in Contrast to Its Predecessor ETC-216

Purpose

Aim of this study was to demonstrate that MDCO-216 (human recombinant Apolipoprotein A-I Milano) does not induce adverse immunostimulation, in contrast to its predecessor, ETC-216, which was thought to contain host cell proteins (HCPs) that elicited an inflammatory reaction.

Methods

Data were taken from a clinical trial in which 24 healthy volunteers (HV) and 24 patients with proven stable coronary artery disease (sCAD) received a single intravenous dose of MDCO-216, ranging 5–40 mg/kg. Additionally, whole blood from 35 HV, 35 sCAD patients and 35 patients requiring acute coronary intervention (aCAD group) was stimulated ex vivo with MDCO-216 and ETC-216.

Results

No inflammatory reaction was observed in HV and sCAD patients following MDCO-216 treatment, judging by body temperature, white cell counts, neutrophil counts, C-reactive protein, circulating cytokines (IL-6, TNF-α), and adverse events. In the ex vivo experiment, the geometric means (SD) of the ratio of MDCO-216 stimulated IL-6 over background levels were 0.8 (1.9), 0.7 (1.5), 1.0 (2.0) for respectively HV, sCAD, aCAD. The corresponding ETC-216 stimulated values were 15.8 (2.9), 9.5 (3.6), 3.8 (4.0). TNF-α results were comparable. Because many ETC-216 stimulated samples had cytokine concentrations >ULOQ, ratios were categorised and marginal homogeneity of the contingency table (MDCO-216 versus ETC-216) was assessed with the Stuart-Maxwell test. P-values were ≤0.0005 for all populations.

Conclusions

MDCO-216 did not induce adverse immunostimulation in HV and sCAD patients, in contrast to ETC-216. Results from the ex vivo stimulation suggests the same holds true for aCAD patients.

Immune response to recombinant Burkholderia pseudomallei FliC

Burkholderia pseudomallei is a flagellated Gram-negative bacterium which is the causative agent of melioidosis. The disease poses a major public health problem in tropical regions and diabetes is a major risk factor. The high mortality rate of melioidosis is associated with severe sepsis which involves the overwhelming production of pro-inflammatory cytokines. Bacterial flagellar protein (flagellin) activates Toll-like receptor 5 (TLR5)-mediated innate immune signaling pathways and induces adaptive immune response. However, previous studies of TLR5 signaling in melioidosis have been performed using recombinant flagellin from Salmonella Typhimurium instead of B. pseudomallei. This study aimed to investigate human innate immune response and antibody response against a recombinant B. pseudomallei flagellin (rFliC). We prepared B. pseudomallei rFliC and used it to stimulate HEK-BlueTM-hTLR5 and THP1-DualTM cells to assess TLR5 activation. Subsequently, whole blood stimulation assays with rFliC were performed ex vivo. TLR5-flagellin interactions trigger activation of transcription factor NF-κB in HEK-BlueTM-hTLR5 cells. Pro-inflammatory cytokine (IL-1β, IL-6, and TNF-α) productions from whole blood in response to rFliC differed between fourteen healthy individuals. The levels of these cytokines changed in a dose and time-dependent manner. ELISA was used to determine rFliC-specific antibodies in serum samples from different groups of melioidosis patients and healthy subjects. IgG antibody to rFliC in melioidosis patients with diabetes were higher compared with non-diabetic patients. Our results show that B. pseudomallei flagellin is a potent immune stimulator and that the immune responses to rFliC are different among individuals. This may provide valuable insights toward the potential use of rFliC in vaccine development.

Chronic Calcium Channel Inhibitor Verapamil Antagonizes TNF-α-Mediated Inflammatory Reaction and Protects Against Inflammatory Arthritis in Mice

It is well established that the tumor necrosis factor-α (TNF-α) plays a dominant role in rheumatoid arthritis (RA). Calcium channel is recently reported to be closely associated with various inflammatory diseases. However, whether chronic calcium channel blocker verapamil plays a role in RA still remains unknown. To investigate the role of verapamil in antagonizing TNF-α-mediated inflammation reaction and the underlying mechanisms, bone marrow-derived macrophages (BMDM) cells were cultured with stimulation of TNF-α, in the presence or absence of verapamil. Inflammation-associated cytokines, including IL-1, IL-6, inducible nitric oxide synthase 2 (NOS-2), and cyclooxygenase-2 (COX-2), were assessed, and verapamil suppressed TNF-α-induced expression of inflammatory cytokines. Furthermore, collagen-induced arthritis (CIA) mice models were established, and arthritis progression was evaluated by clinical and histological signs of arthritis. Treatment of verapamil attenuated inflammation as well as joint destruction in arthritis models. In addition, activity of NF-kB signaling pathway was determined both in vitro and in mice arthritis models, and verapamil inhibited TNF-α-induced activation of NF-kB signaling both in vitro and in mice models. Collectively, chronic calcium channel blocker verapamil may shed light on treatment of inflammatory arthritis and provide a potential therapeutic instrument for RA in the future.

FIP-fve stimulates interferon-gamma production via modulation of calcium release and PKC-alpha activation

Fungal immunomodulatory protein, FIP-fve, has been isolated from Flammulina velutipes, and its immunomodulatory effects are believed to be associated with the enhanced activation of IFN-gamma-releasing Th1 cells. However, the mechanisms of FIP-fve-mediated signal transduction in the regulation of interferon-gamma (IFN-gamma) gene expression in human peripheral blood mononuclear cells (PBMCs) are still poorly understood. Using fluo-3 AM, we found that FIP-fve induces a rapid elevation in calcium concentration. ELISA, RT-PCR and Western blot assays demonstrated significant increases in the production and mRNA expression of IFN-gamma and protein kinase C-alpha (PKC-alpha) activation in activated PBMCs, which were abolished by EGTA, nifedipine and GO6976. In conclusion, Ca2+ release and PKC-alpha activation are required for IFN-gamma production induced by FIP-fve in PBMCs.

Combination use of immune complexes and a Ca2(+) channel blocker azelnidipine enhances interleukin-12 p40 secretion without T helper type 17 cytokine secretion in human monocyte-derived dendritic cells

Immune complexes (ICs) improve the capacity of priming specific CD8(+) cytotoxic T cell responses of dendritic cells (DCs). ICs induce phosphorylation of mitogen-activated protein kinases (MAPK) and calcium influx, although the precise regulating mechanism still remains unclear. In the present study, we investigated the effect of a Ca2(+) channel blocker on the phosphorylation of p38 MAPK and extracellular signal-regulated kinase (ERK) in immature monocyte-derived DCs stimulated with lipopolysaccharide (LPS) or LPS-ICs, and the production of interleukin (IL)-12 family members (p40, p70, IL-23), T helper type 17 (Th17) cytokines (IL-6 and IL-23), tumour necrosis factor (TNF)-alpha and IL-10 were also investigated. In comparison with LPS stimulation, LPS-ICs stimulation enhanced p38 MAPK phosphorylation significantly, which was associated with an increase in IL-12 p40 monomer/homodimer secretion. LPS-ICs also enhanced TNF-alpha and IL-6 secretion, but suppressed IL-23 secretion. The use of azelnidipine (Aze), a long-acting L-type Ca2(+) channel blocker with a high lipid solubility, suppressed p38 MAPK phosphorylation stimulated with LPS or LPS-ICs, but surprisingly enhanced IL-12 p40 monomer/homodimer secretion stimulated with LPS-ICs. This IL-12 p40 secretion-enhancing effect was not accompanied by IL-10 or IL-23 production, but was associated with ERK phosphorylation. The use of Aze did not affect IL-12 p70 production. These results suggest that the use of Aze enhances ICs-mediated IL-12 p40 secretion without additional IL-23 secretion. Therefore, the use of Aze and ICs could be a new therapeutic approach to immunomolecular therapy, as it does not cause Th17 differentiation which induces autoimmunity or reduces anti-tumour immunity.

Expression of Pkd2l2 in testis is implicated in spermatogenesis

Pkd2l2 is a novel member of the polycystic kidney disease (PKD) gene family in mammals. Prominently expressed in testis, this gene is still poorly understood. In this study, reverse transcription polymerase chain reaction (RT-PCR) results showed a time-dependent expression pattern of Pkd2l2 in postnatal mouse testis. Immunohistochemical analysis revealed that Pkd2l2 encoded a protein, polycystin-L2, which was predominantly detectable in the plasma membrane of spermatocytes and round spermatids, as well as in the head and tail of elongating spermatids within seminiferous tubules in mouse testis tissue sections of postnatal day 14 and adult mice. A green fluorescent fusion protein of Pkd2l2 resided in the plasma membrane of HEK 293 and MDCK cells, suggesting that it functions as a plasma membrane protein. Overexpression of Pkd2l2 increased the intracellular calcium concentration of MDCK cells, as detected by flow cytometry. Collectively, these data indicated that Pkd2l2 may be involved in the mid-late stage of spermatogenesis through modulation of the intracellular calcium concentration.