Human monocytoid cell lines as indicators of endotoxin: comparison with rabbit pyrogen and Limulus amoebocyte lysate assay

Detection of innate immune response modulating impurities in therapeutic proteins

Therapeutic proteins can contain multiple impurities, some of which are variants of the product, while others are derived from the cell substrate and the manufacturing process. Such impurities, even when present at trace levels, have the potential to activate innate immune cells in peripheral blood or embedded in tissues causing expression of cytokines and chemokines, increasing antigen uptake, facilitating processing and presentation by antigen presenting cells, and fostering product immunogenicity. Currently, while products are tested for host cell protein content, assays to control innate immune response modulating impurities (IIRMIs) in products are focused mainly on endotoxin and nucleic acids, however, depending on the cell substrate and the manufacturing process, numerous other IIRMI could be present. In these studies we assess two approaches that allow for the detection of a broader subset of IIRMIs. In the first, we use commercial cell lines transfected with Toll like receptors (TLR) to detect receptor-specific agonists. This method is sensitive to trace levels of IIRMI and provides information of the type of IIRMIs present but is limited by the availability of stably transfected cell lines and requires pre-existing knowledge of the IIRMIs likely to be present in the product. Alternatively, the use of a combination of macrophage cell lines of human and mouse origin allows for the detection of a broader spectrum of impurities, but does not identify the source of the activation. Importantly, for either system the lower limit of detection (LLOD) of impurities was similar to that of PBMC and it was not modified by the therapeutic protein tested, even in settings where the product had inherent immune modulatory properties. Together these data indicate that a cell-based assay approach could be used to screen products for the presence of IIRMIs and inform immunogenicity risk assessments, particularly in the context of comparability exercises.

Comparison of inflammatory responses in human cells caused by lipopolysaccharides from Escherichia coli and from indigenous bacteria in aquatic environment

The endotoxic activities of lipopolysaccharides (LPSs) in water samples are usually determined using a Limulus amoebocyte lysate (LAL) assay, but it is known that the determined activities do not always represent their inflammatory potency in humans. In this investigation, the inflammatory responses in three different human cells stimulated with Escherichia coli LPS, keratinocyte, CD14(+) monocyte, and THP-1, were compared using cytokine secretion as biomarkers to develop novel in vitro assay systems for detecting changes in inflammatory potencies of endotoxins in aquatic environment. Only THP-1 with 6-h stimulation showed dose-dependent responses in the range of normal endotoxin levels in aquatic environment. Then, the inflammatory potency of environmental LPS, which was purified from river water, was tested using THP-1. The levels and patterns of cytokine secretion after the environmental LPS stimulation were completely different from E. coli LPS. Interleukin 8 (IL-8) secretions after the environmental LPS stimulation were approximately 10-fold higher than those after E. coli LPS stimulation. The environmental LPS also induced much higher levels of TNF-α secretions in THP-1. These results suggest that a diversity of LPS structures in aquatic environment could contribute to stronger and different inflammatory responses. This investigation indicated that the proposed THP-1 assay system could be useful for detecting the changes in inflammatory potencies caused by aquatic bacteria.

A potential test system for detecting contaminations by bacterial lipoproteins

Biological specimens are often contaminated with bacteria-derived products such as LPS or lipoproteins (LP), which trigger unwanted inflammatory responses in hosts. Whereas a contamination by LPS can be determined by various test systems, a contamination by LP can as yet not be determined. TLR4 and TLR2 are key components of the LPS and the LP receptor complex, respectively. It was tested in this study whether HEK293 cell stably transfected with bovine TLR2 have the ability to react to low concentrations of diacylated and triacylated synthetic LP. The stable cell lines we present here recognize low concentrations of synthetic LP resembling LP of different bacteria. Therefore, these cells are suitable to detect low contaminations present in probes. For example, HEK293 cells stably transfected with bovine TLR2 recognized an egg albumin preparation as contaminated, as evidenced by copious production of IL-8. In contrast, these cells did not respond to a highly purified human serum albumin (HSA) preparation used in the clinic but responded to HSA containing small amounts of diacylated synthetic LP. The TLR4 ligand LPS is often said to activate TLR2. Here we present evidence that LP contaminations are responsible for TLR2 activity. HEK293 cells stably transfected with bovine TLR2 and TLR1 (e.g. clone 1) did not respond to ultra-pure Escherichia coli LPS preparations but acquired responsiveness when stimulated with differently purified commercial LPS. Thus, the described system involving HEK293 cells stably transfected with bovine TLR2 and TLR1 is the first test system described attempting to measure a contamination by LP.

Salmonella synthesizing 1-dephosphorylated [corrected] lipopolysaccharide exhibits low endotoxic activity while retaining its immunogenicity

The development of safe live, attenuated Salmonella vaccines may be facilitated by detoxification of its LPS. Recent characterization of the lipid A 1-phosphatase, LpxE, from Francisella tularensis allowed us to construct recombinant, plasmid-free strains of Salmonella that produce predominantly 1-dephosphorylated lipid A, similar to the adjuvant approved for human use. Complete lipid A 1-dephosphorylation was also confirmed under low pH, low Mg(2+) culture conditions, which induce lipid A modifications. LpxE expression in Salmonella reduced its virulence in mice by five orders of magnitude. Moreover, mice inoculated with these detoxified strains were protected against wild-type challenge. Candidate Salmonella vaccine strains synthesizing pneumococcal surface protein A (PspA) were also confirmed to possess nearly complete lipid A 1-dephosphorylation. After inoculation by the LpxE/PspA strains, mice produced robust levels of anti-PspA Abs and showed significantly improved survival against challenge with wild-type Streptococcus pneumoniae WU2 compared with vector-only-immunized mice, validating Salmonella synthesizing 1-dephosphorylated lipid A as an Ag-delivery system.

A new cell-based innate immune receptor assay for the examination of receptor activity, ligand specificity, signalling pathways and the detection of pyrogens

The pattern recognition receptors (PRRs) of the innate immune system are the first defence line of the immune system. Toll-like receptors (TLRs) are the most well known and the best examined of the PR receptors. In the last years TLRs had been studied in different ways resulting in a lot of new insights in the function and signalling pathways of these receptors. However, it was not possible to investigate individual combinations of the TLRs and their specific ligands, because of the complex network in immune signalling resulting in interference with each other. This work shows a new cell-based assay, established for the analysis of single PRRs or heterodimers. For this purpose NIH3T3 (mouse fibroblasts) were stably transfected with the NF-kappaB-inducible reporter gene secreted alkaline phosphatase (SEAP) together with the corresponding combinations of human TLRs and their co-receptors (e.g. TLR1/2, TLR2/6 and TLR4/CD14). The specificity of the respective cell lines was shown by induction with variations of specific and unspecific ligands (immune-stimulating components of microorganisms or synthetic ligands). Analysis via the NF-kappaB-dependent reporter gene SEAP allows a direct way to detect the human TLR-activity. Our results showed that this assay is highly sensitive and specific for the respective ligands. For the synthetic ligands Pam(2)CysSK(4) the assay demonstrates a detection limit of 1 pg/ml for TLR2/6. In summary, this test system allows the investigation of individual human PRR-receptors in a highly specific way, without interference with other immune components opening new avenues for novel insights in the innate immune system and its applications.

Release of immune modulation factors from platelet concentrates during storage after photochemical pathogen inactivation treatment

BACKGROUND

Blood platelets (PLTs) are critical for hemostasis, and they contain biologically active constituents with the potential to modulate inflammatory responses. This study examined the effects of photochemical pathogen inactivation treatment (PCT) on the release of cytokines and/or chemokines from PLT components.

STUDY DESIGN AND METHODS

Double-dose apheresis PLT components were suspended in plasma-PLT additive solution mixtures and divided into paired therapeutic units. One unit served as an untreated control and the other unit was treated with PCT. PLT concentrations, pH, and levels of cytokines and/or chemokines (CD62p, platelet-derived growth factor-AB, interleukin [IL]-8, soluble CD40 ligand [sCD40L], IL-1beta, and tumor necrosis factor alpha) were measured during 7 days of storage in PLT component supernatants and PLT lysates.

RESULTS

PLT content, pH, and cytokine and/or chemokine content and release from PLT component prepared with PCT were not different (p > 0.05) from paired control components during storage. Levels of sCD40L, however, increased significantly during storage while decreasing in parallel within PLT lysates, although no differences were detected between paired PCT and control PLT component.

CONCLUSION

PCT did not increase the release or secretion of PLT chemokines and/or cytokines over a 7-day period compared to conventional PLT component.

Human monocytoid cells as a model to study Toll-like receptor-mediated activation

THP-1 2A9, a subclone of the monocytoid cell line THP-1 and known to be exquisitely sensitive to LPS, was tested for TNF production following triggering by excess doses of TLR ligands. TLR2, TLR4 and TLR5 agonists, but neither TLR3 nor TLR9 agonists, induced TNF production. When used at lower concentrations, priming by calcitriol strongly influenced the sensitivity of cells to LPS and different TLR2 triggers (lipoteichoic acid (LTA), trispalmitoyl-cysteyl-seryl-lysyl-lysyl-lysyl-lysine (Pam3Cys) and peptidoglycan (PGN)). Priming by calcitriol failed to modulate TLR2 and TLR4 mRNA and cell surface expression of these receptors. TNF signals elicited by TLR2 agonists were blocked by the TLR-specific antibody 2392. CD14-specific antibodies showed variable effects. CD14-specific antibodies inhibited TNF induction by LTA. High concentrations partially inhibited TNF induction by Pam3Cys. The same antibodies failed to inhibit TNF induction by PGN. Thus, THP-1 2A9 cells respond by TNF production to some, but not all TLR agonists, and the wide variety of putative TLR2 agonists interact to variable degrees also with other cell-surface-expressed binding sites such as CD14. THP-1 2A9 cells might provide a model by which to investigate in more detail the interaction of pathogen-associated molecular patterns and monocytoid cell-surface-expressed pattern recognition receptors.

Gene expression profiling of the effects of intravenous immunoglobulin in human whole blood

Intravenous immunoglobulin (IVIG) is involved in many complex mechanisms that act in synergy including expression and function of Fc receptors, complement activation, the cytokine network, interaction with the anti-idiotypic network and modulation of B and T cell activation. To gain insight into the early effects of IVIG on this broad range of activities at the gene level we performed DNA microarray analysis. Human whole blood was incubated in vitro for 4 h followed by extraction of RNA which was hybridized to a chip containing 8793 genes. About 75 upregulated genes and 21 downregulated genes were identified using a cut off for the false discovery rate of 5%. These genes are associated with a wide range of cellular immune functions in line with the broad mechanism of action of IVIG. A striking upregulation of a series of genes coding for chemokines was measured. This finding was confirmed at the protein level as pharmacologically relevant concentrations of CXCL9 and CXCL10 were measured in serum. Interestingly, IVIG shows a partial overlap of its gene expression program with lipopolysaccharide. Our data suggests multiple hypotheses regarding the pharmacology of IVIG that must be validated by complementary studies.

Endotoxin Level Measurement in Hemodialysis Biofilm Using "The Whole Blood Assay"

Biofilms have been found on the inner surface of silicone tubing inside dialysis machines. Endotoxin releasing from those biofilms increases the bioincompatibility of dialysis liquids and leads to long-term inflammatory complications among dialysis patients. Endotoxin measurement is recommended for the control of dialysis liquids. This article describes the use of a new method, the Whole Blood Assay (WBA), for endotoxin quantification in dialysis biofilms. Biofilms were suspended in sterile water by scraping the tubing samples. Diluted blood samples from healthy donors were stimulated overnight with the contaminated suspension. Stimulated mononuclear cells released IL-1beta in response to endotoxins. IL-1beta level was then measured using an ultrasensitive ELISA method. We demonstrated a semilogarithmic model in which the optical densities measured after the ELISA assay increases linearly with the levels of endotoxin. This model allowed the determination of the amount of endotoxins in biofilm samples with a detection limit of 0.032 EU/mL. Most of the time, the amounts of endotoxin measured by the WBA were higher than those measured by the Limulus Amoebocyte Lysate (LAL) assay. This study suggested the presence of "endotoxin-like" compounds different from the lipopolysaccharides that are not detected by the LAL assay. We concluded that the LAL is necessary but insufficient to have a representative quantification of endotoxins that could be hazardous to patient health.

In vitro bioassay of endotoxin using fluorescein as a pH indicator in a macrophage cell culture system

Based on the biological activity of endotoxin, we propose a possible new method for detecting endotoxin using a pH-indication system of macrophage culture media. After RAW 264.7 macrophage cells were treated with lipopolysaccharide (LPS), the addition of fluorescein to the LPS-treated media reproductively reduced its absorption and emission spectra (it was a dose-dependent reduction). The advantages of this LPS-detection method were compared with the Limulus Amebocyte Lysate (LAL) test by using purified bacterial LPS (Salmonella minnessota, Escherichia coli, and Pseudomonas aeruginosa). Additionally, the absorption and fluorescence intensity of fluorescein, following treatment of RAW 264.7 cells with a high concentration of Staphylococcus aureus (Gram-positive, lysed bacteria), could not generally be detected by the LAL test, but they were found to be reduced, in a dose-response relationship, with this new system. The macrophage culture system-method might be a good supplement to the LAL assay for detection of LPS, Gram-negative and Gram-positive bacteria.

International validation of novel pyrogen tests based on human monocytoid cells

It is a requirement that parenteral medicines be tested for pyrogens (fever causing agents) using one of two animal-based tests: the rabbit pyrogen test and the bacterial endotoxin test. Understanding the human fever reaction has led to novel non-animal alternative tests based on in vitro activation of human monocytoid cells in response to pyrogens. Using 13 prototypic drugs, clean or contaminated with pyrogens, we have validated blindly six novel pyrogen tests in ten laboratories. Compared with the rabbit test, the new tests have a lower limit of detection and are more accurate as well as cost and time efficient. In contrast to the bacterial endotoxin test, all tests are able to detect Gram-positive pyrogens. The validation process showed that at least four of the tests meet quality criteria for pyrogen detection. These validated in vitro pyrogen tests overcome several shortcomings of animal-based pyrogen tests. Our data suggest that animal testing could be completely replaced by these evidence-based pyrogen tests and highlight their potential to further improve drug safety.

TNFα Measurement in Rat and Human Whole Blood as an in vitro Method to Assay Pyrogens and its Inhibition by Dexamethasone and Erythromycin

To ensure the safety of potential drugs, pyrogen tests are traditionally performed in rabbits. New methods have been developed as alternatives to the test to reduce the use of experimental animals. Among these methods there are the Limulus amoebocyte lysate test and the determination of cytokine production by human leukocytes and whole blood. When exposed to a range of concentrations of endotoxins, human and rat whole blood release TNFalpha at amounts that are detectable by a commercially available enzyme-linked immunosorbent assay (ELISA). Our results show that the sensitivity of human and rat blood to endotoxins from Salmonella abortus equi and Escherichia coli is similar. In rat blood, TNFalpha was detected after contact with the pyrogens only in fresh blood, collected on the same day of incubation with the pyrogenic substances. The measurement of TNFalpha production would be a reliable alternative to the rabbit pyrogen test. However, given that the addition of erythromycin and dexamethasone inhibited the production of this cytokine, this method is limited when parenteral formulations contain these two drugs. Similar inhibition has been observed in the rabbit test. Additional experiments will be necessary to demonstrate that the rat whole blood test system is useful and reliable for the pyrogens evaluation.

Comparative evaluation of the human whole blood and human peripheral blood monocyte tests for pyrogens

Two different in vitro tests for pyrogens, using human peripheral blood monocytes (PBMNC) and diluted whole blood (WBC), respectively, were applied to different classes of parenteral medicinal products. Many of these products did not have a specified endotoxin limit concentration that was established as the maximum valid dilution to comply with the test. The results of the in vitro tests for pyrogens were compared with the results from the Limulus amoebocyte lysate (LAL) and rabbit pyrogen tests. The Second International Standard for endotoxin was used to calibrate all of the assays and the International Standard for IL-6 was used to calibrate the IL-6 ELISA which provided the readout for the in vitro tests for pyrogens. Preparatory tests were conducted to ensure that the "criteria for validity and precision of the standard curve" were satisfied and that the drugs being tested did not interfere in the tests. The PBMNC/IL-6 test had a detection limit of 0.06 EU/ml and spike recoveries were 62-165%. The whole blood/IL-6 test also had a detection limit of 0.06 EU/ml and spike recoveries were 58-132%. The application to the detection of non-endotoxin pyrogens needs to be evaluated in more detail, but the two in vitro tests for pyrogens showed good agreement overall, both with each other and with the LAL test and the rabbit pyrogen test for the detection of endotoxins.

Endotoxin contamination in wound dressings made of natural biomaterials

Contamination by endotoxin of nine kinds of wound dressings made of natural biomaterials (calcium alginate, collagen, chitin, and poly-L-leucine) was examined with the use of water extracts. By applying the Limulus amoebocyte lysate (LAL) test, high concentrations of endotoxin were detected in extracts from three kinds of products made of calcium alginate. These extracts evoked fever in rabbits and induced the release of a proinflammatory (pyrogenic) cytokine, interleukin-6 (IL-6), from human monocytic cells (MM6-CA8). The effects disappeared when the extracts were treated with endotoxin-removing gel column chromatography or with an endotoxin antagonist, B464, confirming that the contaminating pyrogen was endotoxin. A noteworthy finding was that one of the endotoxin-containing extracts showed very weak IL-6-inducibility in human monocytic cells in contrast to its high pyrogenicity to rabbits. The discrepancy could be explained based on differences between humans and rabbits in sensitivity to the endotoxin, because the extract showed higher proinflammatory-cytokine (TNF-alpha)-inducibility in rabbit whole-blood cells (WBCs) than human WBCs. The results suggest that the LAL test is a useful method of detecting endotoxin contamination in wound dressings and the MM6-CA8 assay is a good supplement to the LAL test for evaluating pyrogenicity in humans accurately.

Endospores of B subtilis are pyrogenic and activate Mono Mac 6 cells: importance of the CD14 receptor

The monocytic cell line Mono Mac 6 is sensitive to pyrogens and interleukin-6 secretion is induced after exposure to pyrogens. The aim of this study is to examine the pyrogenic activity and the interleukin-6-inducing capacity of the Gram-positive B. subtilis bacteria, endospores and isolated cell wall components. Furthermore the involvement of CD14 in activation of interleukin-6 release is investigated. All test substances are pyrogenic in the rabbit pyrogen test. The test substance is incubated with monocytic cells (Mono Mac 6) for 24 h and the secreted interleukin-6 is determined in a sandwich immunoassay. B. subtilis bacteria and endospores induce interleukin-6 in a dose-dependent manner. Endospores are less potent than bacteria. Lipoteichoic acid (LTA) isolated from B. subtilis induces interleukin-6 in a dose-dependent manner, whereas muramyl dipeptide (MDP) is unable to induce interleukin-6. Lipopolysaccharides (LPS) dose-dependently induce interleukin-6 release, but the curve differs from that of LTA both in shape and offset. The interleukin-6 secretion induced by LPS, LTA and B. subtilis bacteria can be blocked by 73-85% by an antibody directed against CD14, whereas the antibody only blocks 25% of B. subtilis endospores-induced interleukin-6 release. The results might indicate that B. subtilis endospores use an additional pathway to CD14 to activate mononuclear cells.

A rapid 'one-plate' in vitro test for pyrogens

A rapid, 'one-plate' monocyte-activation test is described for detecting endotoxin and non-endotoxin pyrogens in parenteral medicinal products. The one-plate test offers useful gains over conventional 'two-plate' (cell culture plate+ELISA plate) tests in terms of its limit of detection, robustness, speed and cost. The 'one-plate' test is likely to be applicable to a wide range of products because it allows less time for product interference in the test. The 'one-plate' test utilises pyrogen-free anti-cytokine (interleukin (IL)-6 or tumour necrosis factor alpha (TNFalpha)) antibodies (Ab), coated and stabilised onto (pyrogen-free) 96-well plates. Monocytes/monocytic cells, endotoxin (lipopolysaccharides, LPS) standard or sample and (pyrogen-free) second (labelled) Ab are cultured together (usually for 2-4 h) on the Ab-coated plate and then the plate is washed and the ELISA completed. There is no transfer from one plate to another and no (further) incubations of (released) cytokine with, first, coating Ab and, then, developing Ab since these steps have already taken place during the initial cell culture. The rapid, 'one-plate' test is readily automated. The preferred readout is IL-6, which gives a limit of detection of 0.015 endotoxin units (EU)/ml with peripheral blood mononuclear cell (PBMNC), 0.03 EU/ml with diluted whole blood and 0.05 EU/ml with a monocytic cell line (MONO MAC 6).

A novel fluorescent protein-based biosensor for gram-negative bacteria

Site-directed mutagenesis of enhanced green fluorescent protein (EGFP) based on rational computational design was performed to create a fluorescence-based biosensor for endotoxin and gram-negative bacteria. EGFP mutants (EGFP(i)) bearing one (G10) or two (G12) strands of endotoxin binding motifs were constructed and expressed in an Escherichia coli host. The EGFP(i) proteins were purified and tested for their efficacy as a novel fluorescent biosensor. After efficient removal of lipopolysaccharide from the E. coli lysates, the binding affinities of the EGFP(i) G10 and G12 to lipid A were established. The K(D) values of 7.16 x 10(-7) M for G10 and 8.15 x 10(-8) M for G12 were achieved. With high affinity being maintained over a wide range of pH and ionic strength, the binding of lipid A/lipopolysaccharide to the EGFP(i) biosensors could be measured as a concentration-dependent fluorescence quenching of the EGFP mutants. The EGFP(i) specifically tagged gram-negative bacteria like E. coli and Pseudomonas aeruginosa, as well as other gram-negative bacteria in contaminated water sampled from the environment. This dual function of the EGFP(i) in detecting both free endotoxin and live gram-negative bacteria forms the basis of the development of a novel fluorescent biosensor.

Evaluation of the in vitro pyrogen test system based on proinflammatory cytokine release from human monocytes: comparison with a human whole blood culture test system and with the rabbit pyrogen test

The reliability of an in vitro pyrogen test system based on proinflammatory cytokine release from human monocytic cells was assessed by comparison with a test system based on a human whole blood culture as well as with the conventional rabbit pyrogen test. The human cells used as the pyrogen indicator cells were newly selected by subcloning of a human monocytic cell line, Mono-Mac-6. The selected cells, named MM6-CA8, responded to various pyrogens, including endotoxin, peptidoglycan (PG), Staphylococcus aureus Cowan 1 (SAC), and poly(I x C), with a high sensitivity and produced proinflammatory cytokines, such as interleukin 1 (IL-1), IL-6, and tumor necrosis factor alpha. Among these cytokines, IL-6 was produced most sensitively in response to traces of the pyrogens and detected in the largest quantities in the culture medium. The cytokine-producing responses of MM6-CA8 cells correlated significantly with the responses of cultured human whole blood, which represents an ex vivo culture test system reproducing pyrogen-induced cytokine production in the human body. In terms of cytokine inducibility, the pyrogens were ranked in the order endotoxin > PG > poly (I. C) > SAC in both culture systems, a ranking which almost agreed with the ranking of their pyrogenicity as assessed by the rabbit pyrogen test. These results suggest that the in vitro responsiveness of MM6-CA8 cells to various pyrogens is highly relevant for human pyrogenic reactions. Therefore, the in vitro test system is useful and reliable for detecting the presence of materials that are pyrogenic for humans.

Chemical and biological evaluation of endotoxin contamination on natural rubber latex products

Relationship between pyrogenicity and bacterial endotoxin contamination on latex products was demonstrated by chemical analysis and biological assays. In commercially available latex products' surveillance, water extracts prepared from one surgical glove and two silicone elastomer-coated Foley catheters sterilized by gamma-irradiation were obviously pyrogenic in rabbits. The induced fever was monophasic at low dose of the pyrogenic extracts and biphasic at high dose. These extracts exhibited limulus amebocyte lysate gelation activity, and induced inflammatory cytokine (interleukin-1, interleukin-6, and tumor necrosis factor-alpha) production from MM6-CA8 human monocytoid cells. These biological properties, including pyrogenicity, completely disappeared by treating the pyrogenic extracts with endotoxin-adsorbent affinity column. Limulus amebocyte lysate activity and cytokine production from MM6-CA8 cells induced by the extracts were significantly decreased by endotoxin inhibitors, an active fragment peptide of an 18-kDa cationic antimicrobial protein and a synthetic lipid A B464 analogue. Furthermore, very small amounts of 2-keto-3-deoxyoctonate and 3-hydroxy fatty acid, which are common constituents of bacterial endotoxins, were detected by gas chromatography-mass spectrometry analysis of the pyrogenic extracts. These findings clearly showed that the pyrogenicity found in these latex products originated from endotoxins contaminating the products.

Ultrasonication of pyrogenic microorganisms improves the detection of pyrogens in the Mono Mac 6 assay

The monocytic cell line Mono Mac 6 is sensitive to pyrogens. When exposed to pyrogens secretion of interleukin-6 is induced. However, some eukaryotic pyrogenic microorganisms are not detectable. The aim of this study is to introduce a pretreatment of samples to expand the detection range of the assay. The interleukin-6 inducing capacity of a broad spectrum of UV-killed and ultrasonicated microorganisms is examined in Mono Mac 6 cells. The interleukin-6 secretion is determined in a sandwich immunoassay (DELFIA). The Mono Mac 6 assay is able to detect UV-killed Bacillus subtilis, Staphylococcus aureus and Salmonella typhimurium, but neither Candida albicans nor Aspergillus niger. After ultrasonication of the microorganisms it is possible to detect C. albicans and A. niger. The interleukin-6 inducing ability of the examined microorganisms is in no case reduced after ultrasonic treatment. However, ultrasonication of S. aureus results in a 100-fold increase in the interleukin-6 response. Even after ultrasonication Streptococcus faecalis can not be detected. Ultrasonication is an easy and simple method for expanding the detection range in the Mono Mac 6 assay.

Interferon-gamma-primed monocytoid cell lines: optimizing their use for in vitro detection of bacterial pyrogens

In order to reduce animal testing for quality control of pharmaceutical agents intended for parenteral use, the Limulus amebocyte lysate (LAL) assay is now being accepted in many cases as an alternative to measuring pyrogenic activity of samples in rabbits. However, since the LAL test is specific for cell wall components from Gram-negative bacteria and is sometimes difficult to perform in samples containing large amounts of protein, this alternative still leaves a considerable diagnostic gap. Here, we have optimized a previously established test based on assessing the formation of neopterin or nitrite in interferon-gamma-treated human (THP-1) or murine (J774A.1, RAW264.7) monocytoid cell lines, respectively, in response to bacterial pyrogens. Optimal results were obtained either with THP-1 cells in serum-containing media and using a high concentration of interferon-gamma (IFN-gamma) or with RAW264.7 cells in serum-free media and independent of the IFN-gamma dose. Results were significantly correlated with those obtained by another cell-culture-based assay in which formation of tumor necrosis factor-alpha by THP-1 1G3 cells was assessed. Also in RAW264.7 murine monocytoid cells, formation of nitrite and of tumor necrosis factor-alpha in response to a variety of samples was correlated. Samples shown to be pyrogenic in rabbits in a previous study were unambiguously detected with the test presented here. As expected, the LAL test was negative with cell-free supernatants from Staphylococcus aureus66 kDa). Taken together, these results indicate that the use of monocytoid cell lines and the detection of metabolites which are triggered in the course of immunostimulation could fill the gap left by the LAL test and help to further reduce animal testing for pyrogens.

A comparative study of Mono Mac 6 cells, isolated mononuclear cells and Limulus amoebocyte lysate assay in pyrogen testing

Pyrogen induced secretion of interleukin 6 (IL-6) in Mono Mac 6 (MM6) cells was measured. The ability of the MM6 cell culture to detect pyrogens was compared to the Limulus amoebocyte lysate (LAL) test and isolated mononuclear cells (MNC). The detection limit of MM6 for lipopolysaccharide (LPS) and Staphylococcus aureus was comparable to that of MNC. Aspergillus niger and Candida albicans induced IL-6 in isolated MNC, but not in MM6. The detection limit for Salmonella typhimurium in the MM6 assay was comparable to that of the LAL assay. As expected, S. aureus and C. albicans did not show any LAL activity. A. niger and Influenza virus showed some activity in the LAL test, but could not be detected by MM6 cells. In conclusion, the MM6 assay is a good supplement to the current pyrogen assays for detection of LPS, S. aureus and S. typhimurium, but the MM6 assay could not detect A. niger, C. albicans and Influenza virus.