Endotoxin contamination in commercially available pokeweed mitogen contributes to the activation of murine macrophages and human dendritic cell maturation

Targeting tumour-associated macrophages in hodgkin lymphoma using engineered extracellular matrix-mimicking cryogels

Tumour-associated macrophages are linked with poor prognosis and resistance to therapy in Hodgkin lymphoma; however, there are no suitable preclinical models to identify macrophage-targeting therapeutics. We used primary human tumours to guide the development of a mimetic cryogel, wherein Hodgkin (but not Non-Hodgkin) lymphoma cells promoted primary human macrophage invasion. In an invasion inhibitor screen, we identified five drug hits that significantly reduced tumour-associated macrophage invasion: marimastat, batimastat, AS1517499, ruxolitinib, and PD-169316. Importantly, ruxolitinib has demonstrated recent success in Hodgkin lymphoma clinical trials. Both ruxolitinib and PD-169316 (a p38 mitogen-activated protein kinase (p38 MAPK) inhibitor) decreased the percent of M2-like macrophages; however, only PD-169316 enhanced the percentage of M1-like macrophages. We validated p38 MAPK as an anti-invasion drug target with five additional drugs using a high-content imaging platform. With our biomimetic cryogel, we modeled macrophage invasion in Hodgkin lymphoma and then used it for target discovery and drug screening, ultimately identifying potential future therapeutics.

Cellular assays to evaluate B-cell function

Inborn errors of immunity (IEI) that present with recurrent infections are largely due to antibody (Ab) deficiencies. Therefore, assessment of the B-cell and Ab compartment is a major part of immunologic evaluation. Here we provide an overview about cellular assays used to study B-cell function and focus on lymphocyte proliferation assay (LPA), opsonophagocytic assay (OPA), and the Enzyme-linked Immunosorbent Spot Assay (ELISPOT) including clinical applications and limitations of these techniques. LPAs assess ex-vivo cell proliferation in response to various stimuli. Clinically available LPAs utilize peripheral blood mononuclear cells and mostly assess T-cell proliferation with pokeweed mitogen considered the most B-cell specific stimulus. In the research setting, isolating B cells or using more B-cell specific stimuli such as CD40L with IL-4/IL-21 or the TLR9 ligand CpG can more specifically capture the proliferative ability of B cells. OPAs are functional in-vitro killing assays used to evaluate the ability of IgG Ab to induce phagocytosis applied when assessing the potency of vaccine candidates or along with avidity assays to evaluate the quality of secreted IgG. The B-cell ELISPOT assesses Ab production at a cellular level and can characterize the Ab response of particular B-cell subtypes. It can be used in patients on IgG therapy by capturing specific Abs produced by individual B cells, which is not affected by exogenous IgG from plasma donors, and when assessing the vaccine response in patients on immunomodulatory drugs that can affect memory B-cell function. Emerging approaches that are only available in research settings are also briefly introduced.

Structure and immunomodulatory activity of a water-soluble α-glucan from Hirsutella sinensis mycelia

Hirsutella sinensis, the anamorph of Ophiocordyceps sinensis (syn. Cordyceps sinensis), is a great substitute for precious and rare wild Cordyceps sinensis to effectively treat a variety of lung and kidney diseases. In this study, an α-glucan (named as HSWP-2a) was obtained by hot water extraction, DEAE-cellulose separation, and Sepharose CL-6B purification from H. sinensis mycelia. Different from known α-glucans, HSWP-2a is an α-(1 → 4)-D-glucan that branched at O-6, O-3, or O-2 with a terminal 1-linked α-D-Glcp as side chain, with an average molecular weight of 870.70 kDa. Immunological tests showed that HSWP-2a could remarkably enhance the phagocytosis of macrophages and increase the production of NO, IL-1β, IL-6, and TNF-α, via activating the p38, JNK, and NF-κB signaling pathways. Moreover, HSWP-2a could significantly promote splenic lymphocyte proliferation. Taken together, HSWP-2a may be potentially utilized as a natural immunomodulatory agent.

Analysis of Antigen-Specific Human Memory B Cell Populations Based on In Vitro Polyclonal Stimulation

Antigen-specific memory B cell (MBC) populations mediate the rapid, strong, and high-affinity secondary antibody responses that play a key role in combating infection and generating protective responses to vaccination. Recently, cell staining with fluorochrome-labeled antigens together with sequencing methods such as Drop-seq and CITE-seq have provided information on the specificity, phenotype, and transcriptome of single MBCs. However, characterization of MBCs at the level of antigen-reactive populations remains an important tool for assessing an individual's B cell immunity and responses to antigen exposure. This is readily performed using a long-established method based on in vitro polyclonal stimulation of MBCs to induce division and differentiation into antibody-secreting cells (ASCs). Post-stimulation antigen-specific measurement of the MBC-derived ASCs (or the secreted antibodies) indicates the size of precursor MBC populations. Additional information about the character of antigen-reactive MBC populations is provided by analysis of MBC-derived antibodies of particular specificities for binding avidity and functionality. This article outlines a simple and reliable strategy for efficient in vitro MBC stimulation and use of the ELISpot assay as a post-stimulation readout to determine the size of antigen-specific MBC populations. Other applications of the in vitro stimulation technique for MBC analysis are discussed. The following protocols are included. © 2020 Wiley Periodicals LLC Basic Protocol 1: Polyclonal stimulation of memory B cells using unfractionated PBMCs Alternate Protocol: Stimulation of small PBMC numbers using 96-well plates with U-bottom wells Basic Protocol 2: ELISpot assay for enumeration of memory B cell-derived antibody-secreting cells.

Mitogen-Induced Interferon Gamma Production in Human Whole Blood: The Effect of Heat and Cations

BACKGROUND

Interferon-gamma release assays (IGRAs) are blood tests used to measure the amount of interferon-γ (IFN-γ) released by T lymphocytes after stimulation by antigens specific for the diagnosis of latent tuberculosis infection. A mitogen serves as a positive control to assess the immune function in IGRAs.

METHODS

This in vitro study was conducted to evaluate IFN-γ production by human whole blood stimulated with heat-treated and/or cation-supplemented phytohemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM), using QuantiFERON-TB Gold Kit ELISA tests.

RESULTS

The optimal concentrations of PWM, Con A and PHA for IGRAs were 2 µg/mL, 5 µg/mL and 10 µg/mL, respectively. The results showed that IFN-γ production in response to PWM was the highest and PHA was the lowest amount. The median values of three mitogens were in the following order: PWM≥Con A≥ positive control>>PHA-P>>negative control. PWM and PHA were heat stable, while Con A was heat sensitive. The mitogen response of lymphocytes to untreated or heat-treated PWM and heat-treated Con A was increased in 1 mM Ca2+-supplemented groups, whereas the response to heat-treated PHA was decreased. Exposure to 1 mM Mg2+ had no effect on untreated or heat-treated PWM, and a concentration of 1 mM Zn2+ inhibited the stimulation of un-treated PWM. We found that calcium supplementation improved the PWM-induced production of IFN-γ.

CONCLUSION

Therefore, PWM is an appropriate mitogen for use as a positive control in IGRAs. It is a potential indicator of cytokine production in the diagnostic as well as research settings, and calcium supplementation improved stimulation.

Intestinal decontamination inhibits TLR4 dependent fibronectin-mediated cross-talk between stellate cells and endothelial cells in liver fibrosis in mice

BACKGROUND & AIMS

Liver fibrosis is associated with angiogenesis and leads to portal hypertension. Certain antibiotics reduce complications of liver failure in humans, however, the effects of antibiotics on the pathologic alterations of the disease are not fully understood. The aim of this study was to test whether the non-absorbable antibiotic rifaximin could attenuate fibrosis progression and portal hypertension in vivo, and explore potential mechanisms in vitro.

METHODS

The effect of rifaximin on portal pressure, fibrosis, and angiogenesis was examined in wild type and Toll-like receptor 4 (TLR4) mutant mice after bile duct ligation (BDL). In vitro studies were carried out to evaluate the effect of the bacterial product and TLR agonist lipopolysaccharide (LPS) on paracrine interactions between hepatic stellate cells (HSC) and liver endothelial cells (LEC) that lead to fibrosis and portal hypertension.

RESULTS

Portal pressure, fibrosis, and angiogenesis were significantly lower in BDL mice receiving rifaximin compared to BDL mice receiving vehicle. Studies in TLR4 mutant mice confirmed that the effect of rifaximin was dependent on LPS/TLR4 pathway. Fibronectin (FN) was increased in the BDL liver and was reduced by rifaximin administration and thus, was explored further in vitro as a potential mediator of paracrine interactions of HSC and LEC. In vitro, LPS promoted FN production from HSC. Furthermore, HSC-derived FN promoted LEC migration and angiogenesis.

CONCLUSIONS

These studies expand our understanding of the relationship of intestinal microbiota with fibrosis development by identifying FN as a TLR4 dependent mediator of the matrix and vascular changes that characterize cirrhosis.

Poke weed mitogen requires Toll-like receptor ligands for proliferative activity in human and murine B lymphocytes

Poke weed mitogen (PWM), a lectin purified from Phytolacca americana is frequently used as a B cell-specific stimulus to trigger proliferation and immunoglobulin secretion. In the present study we investigated the mechanisms underlying the B cell stimulatory capacity of PWM. Strikingly, we observed that highly purified PWM preparations failed to induce B cell proliferation. By contrast, commercially available PWM preparations with B cell activity contained Toll-like receptor (TLR) ligands such as TLR2-active lipoproteins, lipopolysaccharide and DNA of bacterial origin. We show that these microbial substances contribute to the stimulatory activity of PWM. Additional experimental data highlight the capacity of PWM to enable B cell activation by immunostimulatory DNA. Based on these findings we propose that the lectin sensitizes B cells for TLR stimulation as described for B cell receptor ligation and that B cell mitogenicity of PWM preparations results from synergistic activity of the poke weed lectin and microbial TLR ligands present in the PWM preparations.

Identification of AKAP-4 as a new cancer/testis antigen for detection and immunotherapy of prostate cancer

BACKGROUND

Prostate cancer (PC) is the second most common cancer in older men, after skin cancer. PC is difficult to diagnose because the prostate-specific antigen screening method is associated with many false positives. In addition there is a need to develop new and more effective treatments. Among presently available new treatments, immunotherapy is a promising approach. We investigated the expression of the cancer/testis antigen, AKAP-4, in PC patients to evaluate the possibility of exploiting AKAP-4 as a target for immunotherapy.

METHODS

We analyzed normal prostate tissues, 15 patients with PC and the LnCAP PC cell line by immunohistochemistry. We tested AKAP-4 immunogenicity through indirect ELISA on sera from patients and healthy subjects, and we generated in vitro AKAP-4-specific cytotoxic lymphocytes from peripheral blood mononuclear cells.

RESULTS

AKAP-4 was shown both at the cytoplasmic and surface levels of the LnCAP PC cell line. AKAP-4 was also highly expressed in PC cells from patients. We detected specific anti-AKAP-4 circulating immunoglobulins in AKAP-4 positive subjects. Using recombinant AKAP-4 loaded autologous dendritic cells, we generated AKAP-4-specific and HLA-I-restricted cytotoxic T lymphocytes able to kill PC cells in vitro. Further characterization indicated a Th-1 skewing in the cytokine secretion profile of these cells.

CONCLUSIONS

We demonstrate the aberrant expression of AKAP-4 in PC, which will potentially be developed as a biomarker in PC. We provide evidence that AKAP-4 is a potential target for PC adoptive immunotherapy or anti-tumor vaccination.

Glycyrrhetinic acid extracted from Glycyrrhiza uralensis Fisch. induces the expression of Toll-like receptor 4 in Ana-1 murine macrophages

Glycyrrhetinic acid (GA) is an active component of licorice root that has long been used as a herbal medicine for the treatment of peptic ulcer, hepatitis, and pulmonary and skin diseases in Asia and Europe. In this study, we analyzed the effect of GA extracted from Glycyrrhiza uralensis Fisch. on the expression of Toll-like receptors (TLRs) that play key roles in regulating the innate immune response against invading pathogens. Stimulation of Ana-1 murine macrophages with GA induced a significant dose-dependent expression of TLR-4, and its mRNA expression that increased from 3-h post-treatment was approximately fivefold over the level in the mock-treated cells. No endotoxin contamination contributed to the GA-induced TLR-4 expression, because polymyxin B treatment did not alter the upregulated expression of TLR-4 in GA-treated cells. Several molecules, such as myeloid differentiation factor 88, interferon-β, and interleukin-6, which are involved in the TLR-4 downstream signaling pathway, were upregulated significantly in response to GA stimulation. Our findings demonstrate that GA is able to induce the expression of TLR-4 and activate its downstream signaling pathway.

Interaction of β2-glycoprotein I with lipopolysaccharide leads to Toll-like receptor 4 (TLR4)-dependent activation of macrophages

β(2)-Glycoprotein I (β(2)GPI) is an abundant plasma protein that binds to the surface of cells and particles expressing negatively charged lipids, but its physiological role remains unknown. Antibodies to β(2)GPI are found in patients with anti-phospholipid syndrome, a systemic autoimmune disease associated with vascular thrombosis and pregnancy morbidity. Although it has been suggested that anti-β(2)GPI antibodies activate endothelial cells and monocytes by signaling through TLR4, it is unclear how anti-β(2)GPI antibodies and/or β(2)GPI interact with TLR4. A number of mammalian proteins (termed "endogenous Toll-like receptor (TLR) ligands") have been reported to bind to TLR4, but, in most cases, subsequent studies have shown that LPS interaction with these proteins is responsible for TLR activation. We hypothesized that, like other endogenous TLR ligands, β(2)GPI interacts specifically with LPS and that this interaction is responsible for apparent TLR4 activation by β(2)GPI. Here, we show that both LPS and TLR4 are required for β(2)GPI to bind to and activate macrophages. Untreated β(2)GPI stimulated TNF-α production in TLR4-sufficient (but not TLR4-deficient) macrophages. In contrast, neither polymyxin B-treated nor delipidated β(2)GPI stimulated TNF-α production. Furthermore, β(2)GPI bound to LPS in a specific and dose-dependent manner. Finally, untreated β(2)GPI bound to the surface of TLR4-sufficient (but not TLR4-deficient) macrophages. Polymyxin B treatment of β(2)GPI abolished macrophage binding. Our findings suggest a potential new biological activity for β(2)GPI as a protein that interacts specifically with LPS and point to the need to evaluate newly discovered endogenous TLR ligands for potential interactions with LPS.

Pro-inflammatory effects of commercial alpha-lactalbumin on RAW 264.7 macrophages is due to endotoxin contamination

This study investigated the effects of alpha-lactalbumin (alpha-LA) on cellular signaling molecules associated with inflammatory responses in RAW 264.7 macrophages. The results indicated that commercial alpha-LA could increase prostaglandin E(2) (PGE(2)) and the expression of COX-2 via increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38 mitogen-activated protein kinase (MAPK) and jun N-terminal kinase (JNK), and increase nitric oxide (NO) and the expression of iNOS via the activation of ERK1/2 and JNK. Furthermore, commercial alpha-LA could increase nuclear translocation of p65 nuclear factor-kappa B (p65 NF-kappaB) through stimulation on inhibitor kappa B-alpha (IkappaB-alpha) degradation. Since endotoxin also has these effects, we assayed the content of endotoxin in the commercial alpha-LA. We found to our surprise that endotoxin was there and that alpha-LA-induced NO and PGE(2) production could be suppressed by polymyxin B, a specific inhibitor of endotoxin. Thus, the pro-inflammatory effects of commercial alpha-LA might be caused by endotoxin contamination through activation and expression of iNOS and COX-2 which were upregulated by MAPKs or nuclear translocation of p65 NF-kappaB in RAW 264.7 cells. It is therefore crucial to assess the possibility of endotoxin contamination within any biological product being studied for immune augmenting activities before a meaning result can be obtained.

Expressed protein ligation for the preparation of fusion proteins with cell penetrating peptides for endotoxin removal and intracellular delivery

Expressed protein ligation (EPL) is a useful method for the native chemical ligation of proteins with other proteins or peptides. This study assessed the practicability of EPL in the preparation of fusion proteins of enhanced green fluorescent protein (EGFP) with chemically synthesized cell-penetrating peptides (CPPs) for intracellular delivery. Using intein-mediated purification with an affinity chitin-binding tag (IMPACT) system, the thioester of EGFP (EGFP-SR) was prepared. Optimization of the ligation of EGFP-SR with arginine 12-mer (R12) produced the fusion protein in high yield. The EPL procedure also allows the preparation of EGFP-R12 containing a low level of endotoxin (ET), via the satisfactory ET removal of EGFP-SR prior to ligation with the R12 peptide. Fusion proteins of EGFP with R12 and the d-isomer of R12 prepared by EPL showed similar levels of cellular uptake compared to the fusion protein directly expressed in Escherichiacoli.

Lipopolysaccharide is a frequent and significant contaminant in microglia-activating factors

Lipopolysaccharide (LPS/endotoxin) is a potent immunologic stimulant. Many commercial-grade reagents used in research are not screened for LPS contamination. LPS induces a wide spectrum of proinflammatory responses in microglia, the immune cells of the brain. Recent studies have demonstrated that a broad range of endogenous factors including plasma-derived proteins and bioactive phospholipids can also activate microglia. However, few of these studies have reported either the LPS levels found in the preparations used or the effect of LPS inhibitors such as polymyxin B (PMX) on factor-induced responses. Here, we used the Limulus amoebocyte lysate assay to screen a broad range of commercial- and pharmaceutical-grade proteins, peptides, lipids, and inhibitors commonly used in microglia research for contamination with LPS. We then characterized the ability of PMX to alter a representative set of factor-induced microglial activation parameters including surface antigen expression, metabolic activity/proliferation, and NO/cytokine/chemokine release in both the N9 microglial cell line and primary microglia. Significant levels of LPS contamination were detected in a number of commercial-grade plasma/serum- and nonplasma/serum-derived proteins, phospholipids, and synthetic peptide preparations, but not in pharmaceutical-grade recombinant proteins or pharmacological inhibitors. PMX had a significant inhibitory effect on the microglia-activating potential of a number of commercial-, but not pharmaceutical-grade, protein preparations. Novel PMX-resistant responses to alpha(2)-macroglobulin and albumin were incidentally observed. Our results indicate that LPS is a frequent and significant contaminant in commercial-grade preparations of previously reported microglia-activating factors. Careful attention to LPS levels and appropriate controls are necessary for future studies in the neuroinflammation field.