Activation of alpha-human tumour necrosis factor (TNF-alpha) by human monocytes (THP-1) exposed to 2-chloroethyl ethyl sulphide (H-MG)

A review of Sulfur Mustard-induced pulmonary immunopathology: An Alveolar Macrophage Approach

Despite many studies investigating the mechanism of Sulfur Mustard (SM) induced lung injury, the underlying mechanism is still unclear. Inflammatory and subsequent fibroproliferative stages of SM-toxicity are based upon several highly-related series of events controlled by the immune system. The inhalation of SM gas variably affects different cell populations within the lungs. Various studies have shown the critical role of macrophages in triggering a pulmonary inflammatory response as well as its maintenance, resolution, and repair. Importantly, macrophages can serve as either pro-inflammatory or anti-inflammatory populations depending on the present conditions at any pathological stage. Different characteristics of macrophages, including their differentiation, phenotypic, and functional properties, as well as interactions with other cell populations determine the outcomes of lung diseases and the extent of long- or short-term pulmonary damage induced by SM. In this paper, we summarize the current state of knowledge regarding the role of alveolar macrophages and their mediators in the pathogenesis of SM in pulmonary injury. Investigating the specific cells and mechanisms involved in SM-lung injury may be useful in finding new target opportunities for treatment of this injury.

From the Cover: Catalytic Antioxidant Rescue of Inhaled Sulfur Mustard Toxicity

Sulfur mustard (bis 2-chloroethyl ethyl sulfide, SM) is a powerful bi-functional vesicating chemical warfare agent. SM tissue injury is partially mediated by the overproduction of reactive oxygen species resulting in oxidative stress. We hypothesized that using a catalytic antioxidant (AEOL 10150) to alleviate oxidative stress and secondary inflammation following exposure to SM would attenuate the toxic effects of SM inhalation. Adult male rats were intubated and exposed to SM (1.4 mg/kg), a dose that produces an LD₅₀ at approximately 24 h. Rats were randomized and treated via subcutaneous injection with either sterile PBS or AEOL 10150 (5 mg/kg, sc, every 4 h) beginning 1 h post-SM exposure. Rats were euthanized between 6 and 48 h after exposure to SM and survival and markers of injury were determined. Catalytic antioxidant treatment improved survival after SM inhalation in a dose-dependent manner, up to 52% over SM PBS at 48 h post-exposure. This improvement was sustained for at least 72 h after SM exposure when treatments were stopped after 48 h. Non-invasive monitoring throughout the duration of the studies also revealed blood oxygen saturations were improved by 10% and clinical scores were reduced by 57% after SM exposure in the catalytic antioxidant treatment group. Tissue analysis showed catalytic antioxidant therapy was able to decrease airway cast formation by 69% at 48 h post-exposure. To investigate antioxidant induced changes at the peak of injury, several biomarkers of oxidative stress and inflammation were evaluated at 24 h post-exposure. AEOL 10150 attenuated SM-mediated lung lipid oxidation, nitrosative stress and many proinflammatory cytokines. The findings indicate that catalytic antioxidants may be useful medical countermeasure against inhaled SM exposure.

Lipopolysaccharide induced protection against sulfur mustard cytotoxicity in RAW264.7 cells through generation of TNF-alpha

Sulfur mustard (HD), a very potent alkylating agent and lipopolysacchride (LPS), are both well characterized inflammatory factors. We have found that concomitant exposure of murine macrophage cells (RAW264.7) to LPS and HD induced protection against HD induced cytotoxicity. Both HD and LPS induce release of inflammatory markers in RAW264.7 cells. However, there are marked differences in the repertoire of inflammatory factors released by the two toxins: While exposure to HD, induced a dose-dependant death of these cells, no significant change in survival rate was observed following LPS (1-100 ng/ml) exposure. Additionally, LPS elicited a robust nitric oxide (NO) and TNF-alpha secretion whereas HD was practically ineffective. Both toxins increased PGE(2) secretion in a concentration dependent manner. Treatment of HD-exposed RAW264.7 cells with anti-inflammatory drugs such as dexamethazone (5 muM), voltaren (diclofenac) (8 muM) or doxycycline (5 muM), decreased the release of cytokines but had no effect on cell viability. Simultaneous application of LPS (100 ng/ml) and HD (20-100 muM) resulted in an amelioration of HD cytotoxicity. Adding the NO generator S-nitrosoglutathione (GSNO) or inhibiting NO production using L-N(G)-monomethyl Arginine, had no effect on cell viability. Moreover, addition of PGE(2) (20 ng/ml) failed to induce any changes in cell viability under basal or HD-induced toxicity. In contrast, TNF-alpha (20 ng/ml) provided remarkable protection against HD-induced cell death. These findings strongly suggest that LPS exerts its protective action against HD toxicity through the generation of TNF-alpha and may provide better understanding of the mechanism of cytoprotection.

Sulfur mustard-induced pulmonary injury: therapeutic approaches to mitigating toxicity

Sulfur mustard (SM) is highly toxic to the lung inducing both acute and chronic effects including upper and lower obstructive disease, airway inflammation, and acute respiratory distress syndrome, and with time, tracheobronchial stenosis, bronchitis, and bronchiolitis obliterans. Thus it is essential to identify effective strategies to mitigate the toxicity of SM and related vesicants. Studies in animals and in cell culture models have identified key mechanistic pathways mediating their toxicity, which may be relevant targets for the development of countermeasures. For example, following SM poisoning, DNA damage, apoptosis, and autophagy are observed in the lung, along with increased expression of activated caspases and DNA repair enzymes, biochemical markers of these activities. This is associated with inflammatory cell accumulation in the respiratory tract and increased expression of tumor necrosis factor-α and other proinflammatory cytokines, as well as reactive oxygen and nitrogen species. Matrix metalloproteinases are also upregulated in the lung after SM exposure, which are thought to contribute to the detachment of epithelial cells from basement membranes and disruption of the pulmonary epithelial barrier. Findings that production of inflammatory mediators correlates directly with altered lung function suggests that they play a key role in toxicity. In this regard, specific therapeutic interventions currently under investigation include anti-inflammatory agents (e.g., steroids), antioxidants (e.g., tocopherols, melatonin, N-acetylcysteine, nitric oxide synthase inhibitors), protease inhibitors (e.g., doxycycline, aprotinin, ilomastat), surfactant replacement, and bronchodilators. Effective treatments may depend on the extent of lung injury and require a multi-faceted pharmacological approach.

The influence of N-acetyl-L-cysteine on oxidative stress and nitric oxide synthesis in stimulated macrophages treated with a mustard gas analogue

Background

Sulphur mustard gas, 2, 2'-dichlorodiethyl sulphide (HD), is a chemical warfare agent. Both mustard gas and its monofunctional analogue, 2-chloroethyl ethyl sulphide (CEES), are alkylating agents that react with and diminish cellular thiols and are highly toxic. Previously, we reported that lipopolysaccharide (LPS) significantly enhances the cytotoxicity of CEES in murine RAW 264.7 macrophages and that CEES transiently inhibits nitric oxide (NO) production via suppression of inducible NO synthase (iNOS) protein expression. NO generation is an important factor in wound healing. In this paper, we explored the hypotheses that LPS increases CEES toxicity by increasing oxidative stress and that treatment with N-acetyl-L-cysteine (NAC) would block LPS induced oxidative stress and protect against loss of NO production. NAC stimulates glutathione (GSH) synthesis and also acts directly as a free radical scavenger. The potential therapeutic use of the antibiotic, polymyxin B, was also evaluated since it binds to LPS and could thereby block the enhancement of CEES toxicity by LPS and also inhibit the secondary infections characteristic of HD/CEES wounds.

Results

We found that 10 mM NAC, when administered simultaneously or prior to treatment with 500 μM CEES, increased the viability of LPS stimulated macrophages. Surprisingly, NAC failed to protect LPS stimulated macrophages from CEES induced loss of NO production. Macrophages treated with both LPS and CEES show increased oxidative stress parameters (cellular thiol depletion and increased protein carbonyl levels). NAC effectively protected RAW 264.7 cells simultaneously treated with CEES and LPS from GSH loss and oxidative stress. Polymyxin B was found to partially block nitric oxide production and diminish CEES toxicity in LPS-treated macrophages.

Conclusion

The present study shows that oxidative stress is an important mechanism contributing to CEES toxicity in LPS stimulated macrophages and supports the notion that antioxidants could play a therapeutic role in preventing mustard gas toxicity. Although NAC reduced oxidative stress in LPS stimulated macrophages treated with CEES, it did not reverse CEES-induced loss of NO production. NAC and polymyxin B were found to help prevent CEES toxicity in LPS-treated macrophages.

Inhibition of cholinephosphotransferase activity in lung injury induced by 2-chloroethyl ethyl sulfide, a mustard analog

Exposure to mustard gas causes inflammatory lung diseases including acute respiratory distress syndrome (ARDS). A defect in the lung surfactant system has been implicated as a cause of ARDS. A major component of lung surfactant is dipalmitoyl phosphatidylcholine (DPPC) and the major pathway for its synthesis is the cytidine diphosphocholine (CDP-choline) pathway. It is not known whether the ARDS induced by mustard gas is mediated by its direct effects on some of the enzymes in the CDP-choline pathway. In the present study we investigated whether mustard gas exposure modulates the activity of cholinephosphotransferase (CPT) the terminal enzyme by CDP-choline pathway. Adult guinea pigs were intratracheally infused with single doses of 2-chloroethyl ethyl sulfide (CEES) (0.5 mg/kg b.wt. in ethanol). Control animals were injected with vehicles only. The animals were sacrificed at different time and the lungs were removed after perfusion with physiological saline. CPT activity increased steadily up to 4 h and then decreased at 6 h and stabilized at 7 days in both mitochondria and microsomes. To determine the dose-dependent effect of CEES on CPT activity we varied the doses of CEES (0.5-6.0 mg/kg b.wt.) and sacrificed the animals at 1 h and 4 h. CPT activity showed a dose-dependent increase of up to 2.0 mg/kg b.wt. of CEES in both mitochondria and microsomes then decreased at 4.0 mg/kg b.wt. For further studies we used a fixed single dose of CEES (2.0 mg/kg b.wt.) and fixed exposure time (7 days). Lung injury was determined by measuring the leakage of iodinated-bovine serum albumin into lung tissue and expressed as the permeability index. CEES exposure (2.0 mg/kg b.wt. for 7 days) caused a significant decrease of both CPT gene expression (approximately 1.7-fold) and activity (approximately 1.5-fold) in the lung. This decrease in CPT activity was not associated with any mutation of the CPT gene. Previously we reported that CEES infusion increased the production of ceramides which are known to modulate PC synthesis. To determine whether ceramides affect microsomal CPT activity the lung microsomal fraction was incubated with different concentrations of C(2)-ceramide prior to CPT assay. CPT activity decreased significantly with increasing dose and time. The present study indicates that CEES causes lung injury and significantly decreases CPT gene expression and activity. This decrease in CPT activity was not associated with any mutation of the CPT gene is probably mediated by accumulation of ceramides. CEES induced ceramide accumulation may thus play an important role in the development of ARDS by modulating CPT enzyme.

Involvement of tumor necrosis factor-alpha in sulfur mustard-induced skin lesion; effect of topical iodine

Sulfur mustard (SM), also termed mustard gas, is a potent vesicant that elicits an inflammatory response upon exposure of the skin. Evaluation of mouse ear 3 h after SM exposure revealed acute inflammatory-cell aggregates in the vascular beds accompanied by strongly TNF-alpha-positive neutrophils. Eight hours after SM exposure, this phenomenon became intensified and associated with infiltration into the adjacent dermis. In ear skin topically treated with iodine, however, no inflammatory cells were observed 3 h after SM exposure; 8 h postexposure, blood vessels contained very few TNF-alpha-positive inflammatory cells. Since TNF-alpha induction was shown to be associated with reactive oxygen species production, we studied the effect of iodine on activated peritoneal mouse neutrophils. Iodine elicited a concentration-dependent reduction in the oxidative burst of activated neutrophils. Iodine also scavenged hydroxyl radicals generated by glucose oxidase in a concentration-dependent manner. The involvement of TNF-alpha in SM-induced skin toxicity was confirmed by reduction of 49 and 30% in ear edema following administration of 1 and 2 mug anti-TNF-alpha antibodies, respectively. These findings were corroborated by quantitative analysis of the histological findings showing 46% reduction in acute inflammation and no signs of subacute inflammation in the treated group, in contrast to the control group treated with SM only. Other epidermal (microblister formation, ulceration, and necrosis) and dermal (neutrophilia, hemorrhage, and necrosis) parameters also showed marked reductions in the antibodies-treated group in comparison to controls. The combination of iodine and antiTNF-alpha antibodies might constitute a new approach for treatment of SM-exposed individuals.

Biochemical changes in mouse lung after subcutaneous injection of the sulfur mustard 2-chloroethyl 4-chlorobutyl sulfide

Sulfur mustard (HD) is a vesicant-type chemical warfare agent (CWA) introduced in World War I which continues to be produced, stockpiled, and occasionally deployed by some countries, and could be used potentially by terrorists. Exposure to HD can cause erythema, blisters, corneal opacity, and airway damage. We have reported previously that subcutaneous (SC) injection of immunodeficient athymic nude mice with the half mustard butyl 2-chloroethyl sulfide (BCS) causes systemic biochemical changes in several organs distal to the exposure site. In the present study, we examined the response of non-immunodeficient Swiss Webster mice to the mustard, 2-chloroethyl 4-chlorobutyl sulfide (CECBS). In a pilot study, we found that a single SC injection of 20-25 microl/mouse causes death within 24h. Consequently, we used 5 microl/mouse (approx. 0.017 mg/kg body weight) of neat CECBS or an equal volume of saline as control. We examined the lungs after 1, 24, and 48 h for biochemical changes including total and oxidized glutathione, protein, DNA, and lipid peroxidation contents in tissue homogenate, and superoxide dismutase, catalase, glucose-6-phosphate dehydrogenase, and glutathione S-transferases activities in the cytosol. After 1h and/or 24h, we found statistically significant changes that were resolved by 48 h. These changes mimicked those of HD and BCS and were generally consistent with free radical-mediated oxidative stress. The implications of these observations are two-fold. First, dermal exposure to low-dose mustard gas could elicit systemic changes impacting distal organs such as the lungs. It also suggests that antioxidants could potentially modulate the response and reduce the damage. Second, although the use of known CWAs such as HD is prohibited, analogs that are not recognized as agents are as toxic and could be dangerous if acquired and used by potential terrorists.

Prophylactic protection by N-acetylcysteine against the pulmonary injury induced by 2-chloroethyl ethyl sulfide, a mustard analogue

Mustard gas exposure causes adult respiratory distress syndrome associated with lung injury. The purpose of this study was to investigate whether an antioxidant, such as N-acetylcysteine (NAC), has any protective effect. Guinea pigs were given single exposure (0.5-6 mg/kg body weight) of 2-chloroethyl ethyl sulfide (CEES) as a mustard analogue intratracheally and maintained for various lengths of time (1 h to 21 days). Within 1 h of CEES infusion at 4 mg/kg, high levels of tumor necrosis factor alpha (TNF-alpha), ceramides, and nuclear factor kappaB accumulated in lung and alveolar macrophages. Both acid and neutral sphingomyelinases were activated within 4 h. These signal transduction events were associated with alteration in the oxygen defense system. Within 1 h of exposure to CEES (6 mg/kg body weight), there was 10-fold increase in the (125)I-BSA leakage into lung tissue, indicating severe lung injury. Although low level of CEES exposure (0.5 mg/kg body weight) produced symptoms of chemical burn in lung as early as 1 h after exposure, the severity of edema, congestion, hemorrhage, and inflammation increased progressively with time (1 h to 21 days). Feeding of single dose of NAC (0.5 g) by gavage just before the CEES infusion was ineffective to counteract these effects. However, consumption of the antioxidant in drinking water for 3 or 30 days prior to CEES exposure significantly inhibited the induction of TNF-alpha, activation of neutral and acid sphingomyelinases, production of ceramides, activation of caspases, leakage of (125)I-bovine serum albumin ((125)I-BSA) into lung tissue, and histological alterations in lung. Pretreatment with NAC for 3 and 30 days protected against 69-76% of the acute lung injury. Therefore, NAC may be an antidote for CEES-induced lung injury.

Signal transduction events in lung injury induced by 2-chloroethyl ethyl sulfide, a mustard analog

Sulfur mustard has been used as a vesicant chemical warfare agent. To understand the mechanism by which mustard gas exposure causes respiratory damage, we have used 2-chloroethyl ethyl sulfide (CEES) as a mustard analog. Our initial studies have shown that guinea pigs exposed to CEES intratracheally accumulate high levels of TNF-alpha. Accumulation of TNF-alpha leads to activation of both acid and neutral sphingomyelinases, resulting in high accumulation of ceramides, a second messenger involved in cell apoptosis. In addition, NF-kappa B was activated for a short period (1-2 h after exposure) as determined by mobility shift assay. Supershift assays indicated that both p50 and p65 of NF-kappa B were activated due to CEES exposure. However, NF-kappa B rapidly disappeared after 2 h. It is possible that the initial activation of NF-kappa B was an adaptive response to protect the cells from damage since NF-kappa B is known to inhibit TNF-alpha/ceramide-induced cell apoptosis. Since NF-kappa B disappeared after 2 h, the cells continued being damaged owing to accumulation of ceramides and activation of several caspases, leading to apoptosis.

Putative role of proteolysis and inflammatory response in the toxicity of nerve and blister chemical warfare agents: implications for multi-threat medical countermeasures

Despite the contrasts in chemistry and toxicity, for blister and nerve chemical warfare agents there may be some analogous proteolytic and inflammatory mediators and pathological pathways that can be pharmacological targets for a single-drug multi-threat medical countermeasure. The dermal-epidermal separation caused by proteases and bullous diseases compared with that observed following exposure to the blister agent sulfur mustard (2,2'-dichlorodiethyl sulfide) has fostered the hypothesis that sulfur mustard vesication involves proteolysis and inflammation. In conjunction with the paramount toxicological event of cholinergic crisis that causes acute toxicity and precipitates neuronal degeneration, both anaphylactoid reactions and pathological proteolytic activity have been reported in nerve-agent-intoxicated animals. Two classes of drugs already have demonstrated multi-threat activity for both nerve and blister agents. Serine protease inhibitors can prolong the survival of animals intoxicated with the nerve agent soman and can also protect against vesication caused by the blister agent sulfur mustard. Poly (ADP-ribose) polymerase (PARP) inhibitors can reduce both soman-induced neuronal degeneration and sulfur-mustard-induced epidermal necrosis. Protease and PARP inhibitors, like many of the other countermeasures for blister and nerve agents, have potent primary or secondary anti-inflammatory pharmacology. Accordingly, we hypothesize that drugs with anti-inflammatory actions against either nerve or blister agent might also display multi-threat efficacy for the inflammatory pathogenesis of both classes of chemical warfare agent.

Lipopolysaccharide enhances the cytotoxicity of 2-chloroethyl ethyl sulfide

BACKGROUND

The bacterial endotoxin, lipopolysaccharide (LPS), is a well-characterized inflammatory factor found in the cell wall of Gram-negative bacteria. In this investigation, we studied the cytotoxic interaction between 2-chloroethyl ethyl sulfide (CEES or ClCH2CH2SCH2CH3) and LPS using murine RAW264.7 macrophages. CEES is a sulfur vesicating agent and is an analog of 2,2'-dichlorodiethyl sulfide (sulfur mustard). LPS is a ubiquitous natural agent found in the environment. The ability of LPS and other inflammatory agents (such as TNF-alpha and IL-1beta) to modulate the toxicity of CEES is likely to be an important factor in the design of effective treatments.

RESULTS

RAW 264.7 macrophages stimulated with LPS were found to be more susceptible to the cytotoxic effect of CEES than unstimulated macrophages. Very low levels of LPS (20 ng/ml) dramatically enhanced the toxicity of CEES at concentrations greater than 400 microM. The cytotoxic interaction between LPS and CEES reached a maximum 12 hours after exposure. In addition, we found that tumor necrosis factor-alpha (TNF-alpha) and interleukin-1-beta (IL-1-beta) as well as phorbol myristate acetate (PMA) also enhanced the cytotoxic effects of CEES but to a lesser extent than LPS.

CONCLUSION

Our in vitro results suggest the possibility that LPS and inflammatory cytokines could enhance the toxicity of sulfur mustard. Since LPS is a ubiquitous agent in the natural environment, its presence is likely to be an important variable influencing the cytotoxicity of sulfur mustard toxicity. We have initiated further experiments to determine the molecular mechanism whereby the inflammatory process influences sulfur mustard cytotoxicity.

Protection from half-mustard-gas-induced acute lung injury in the rat

The chemical warfare agent analog, 2-chloroethyl ethyl sulfide, known as 'half-mustard gas' (HMG), is less toxic and less of an environmental hazard than the full molecule and has been shown to produce an acute lung injury in rats when instilled via intrapulmonary injection. This injury is characterized by massive, localized hemorrhage and edema into the alveolar compartment and can be quantitated by measuring extravasation of (125)I-bovine serum albumin into the extravascular compartment. Employing this rat model of HMG-induced lung injury, we observed significant attenuation of the pulmonary injury when experimental animals were complement or neutrophil depleted prior to HMG challenge. Significant protection also was provided by the use of antioxidants such as catalase, dimethyl sulfoxide, dimethyl thiourea, resveratrol and N-acetyl-L-cysteine (NAC). The last compound showed protection from lung injury as high as 70% and was still effective even when given up to 90 min after exposure of the lungs to HMG. These data suggest that acute lung injury caused by exposure to HMG may be related partially to complement mediated pathways and the generation by neutrophils of toxic oxygen species The data indicate that NAC is an effective antidote against HMG-induced acute lung injury in the rat.

The role of interleukin-6 (IL-6) in human sulfur mustard (HD) toxicology

The authors applied in vitro models of controlled damage to human epidermal keratinocytes (HEKs), human skin fibroblasts (HSFs), and human breast skin tissue (HBST) to examine the mechanism responsible for sulfur mustard (HD)-induced interleukin-6 (IL-6) alterations. Treatment with 100 microM HD for 24 hours resulted in a significant increased amount of IL-6 being secreted by HEKs (HD-exposed to control ratio [E/C] = 4.15 +/- 0.07) and by HSFs (E/C = 7.66 +/- 0.04). Furthermore, the HD-induced secretion of IL-6 in HEKs was neutralized with monoclonal human IL-6 antibodies. The secretion of IL-6 in HBST supernatant exposed to HD produced conflicting results. Although an increase of IL-6 was observed in control superfusion media from HBST, IL-6 levels were observed to decrease as the concentration of HD increased. Time course of IL-6 mRNA levels were performed using a competitive polymerase chain reaction (PCR) and human IL-6 mRNA assay detection kit in control and HD (100 microM)-treated HEKs cells. IL-6 mRNA transcripts in HD-exposed HEKs were first observed within 2 hours, dropped at 5 to 6 hours, and increased by approximately 2.2-fold and 8.5-fold at 24 to 48 hours after HD exposure, respectively, as detected by the Xplore mRNA Quantification System. Surface-enhanced laser desorption ionization (SELDI) mass spectrometry was also applied to study the secretion pattern of IL-6 on lysate preparations of HBST. A peak in the area of 23,194 to 23,226 Da was detected using antibody coupled to the chip. This peak was assigned to correspond to the mass of the IL-6 glycoprotein. Recombinant human IL-6 (rhIL-6) exposed to HD lacked the second disulfide bridge and was partially unfolded, as determined by nuclear magnetic resonance-nuclear Overhauser enhancement and exchange spectroscopy (NMR-NOESY). The disappearance of the resonance peak at 3.54 ppm and the appearance of a new chemical shift at 1.85 ppm suggested that a change in structure had occurred in the presence of HD. From the data, the possibility cannot be excluded that IL-6 might be involved in the early event of structural changes of the signal transducer glycoprotein that indirectly initiates the cascade of events such as skin irritation and blister formation observed in the pathophysiology of HD injury.

Exposure of human epidermal keratinocyte cell cultures to sulfur mustard promotes binding of complement C1q: implications for toxicity and medical countermeasures

Sulfur mustard (HD)-increased proteolytic activity, HD-enhanced expression of Fc receptor (FcR) on human epidermal keratinocytes (HEK) and associated inflammatory responses may contribute to HD pathology. Like the FcR, the first component of the classical complement (C') cascade, C1q, binds to the Fc region of antibody to mediate inflammatory responses. Complement C1q binds specifically to the C1q receptor (C1qR) on the blebs of apoptotic human keratinocytes and is proposed as a cell surface marker for apoptosis. Assays by fluorescent antibodies demonstrated significantly enhanced binding of C1q to HEK cell cultures exposed to HD. The cell populations of HEK that showed enhanced C1q binding also demonstrated an intermediate uptake of propidium iodide that was greater than in viable unexposed cells but less than in dead cells. The HD-enhanced C1q binding was concentration-dependent, negative by flow cytometry or weakly positive by digital scanning microscopy at 100 microM and positive by both methods at 300 microM. Binding of C1q was also time-dependent, weakly positive at 8 h, and positive at 16 and 24 h after HD exposure. The HD-increased C1qR that binds C1q to the surface of HEK might be a contributing mechanism or a marker for the inflammation and vesication associated with HD exposure.