Factors which affect superoxide anion release from rat alveolar macrophages

In order to investigate some of the characteristics of superoxide anion release from alveolar macrophages, the effects of substances known to influence superoxide release from polymorphonuclear leukocytes (PMN) were studied in rat alveolar macrophages. There is a relatively small, but constant, amount of superoxide released from alveolar macrophages at rest. The amount released increases 5- to 6-fold and becomes maximal in about 20-30 min following exposure to unopsonized zymosan particles. The rate of superoxide release is maximal only 2 min after exposure of the cells to particles, i.e., long before particle uptake is complete. In addition to particles, release of superoxide anion can be stimulated by phorbol-12-myristate-13-acetate (PMA). Lectins and chemotactic factors, which stimulate release in PMN, have little or no effect in alveolar macrophages. Superoxide release during exposure to zymosan appears to be dependent upon extracellular Ca++. Also, the release mechanism can be affected by the addition of cyclic AMP or various protein modifiers to the medium. Since many of these findings differ from those reported by others for PMN, the control of superoxide anion release from alveolar macrophages and PMN is probably different.     

Superoxide anion release induced by platelet-activating factor is increased in human alveolar macrophages from smokers.

This study was designed to investigate the effects of the platelet-activating factor (PAF) on the superoxide anion production (O2.) of human alveolar macrophages (AM) from nonsmoking (n = 18) and smoking (n = 30) subjects. Freshly isolated cells were stimulated with (PAF) or with a phorbol ester (phorbol 12-myristate 13 acetate (PMA)). Stimulation with PAF led to a dose-dependent increase of O2. production by AM in both groups. The median effective dose (EC50) for PAF action on O2. production of smoker AM was 0.5 x 10(-8) M, compared to nonsmoker AM with an EC50 of 1.0 x 10(-7) M. This effect of PAF was blockable by the PAF-antagonist WEB 2086 in a dose-dependent manner. Comparison of the relative increase of O2. production after PAF-stimulation showed that smoker cells were significantly more sensitive to PAF than nonsmoker cells (p less than 0.01). In contrast to the findings with PAF, the relative increase of O2. production after PMA-stimulation showed no differences between smoker and nonsmoker AM. Our data suggest that AM from smoking subjects are more sensitive to PAF than AM from nonsmokers.     

Acute effect of smoking on superoxide production by pulmonary alveolar macrophages

We determined the acute effect of smoking on superoxide (O ₂ ⁻ ) production by pulmonary alveolar macrophages (AM) in 32 smokers who had bronchoalveolar lavage both before and after smoking. In 18 subjects, AM were obtained either 10, 30, or 60 minutes after the subjects had smoked 2 cigarettes, while in 14, AM were recovered either at 2, 10, or 60 minutes after they had smoked 4 cigarettes. Prior to smoking, O ₂ ⁻ production by AM was significantly greater in smokers than in 8 control nonsmokers for unstimulated AM, as well as for AM stimulated by zymosan and phorbol myristate acetate. Superoxide production by unstimulated AM increased significantly 1 h after subjects had smoked 2 cigarettes, to 140.8 ± SD 14.7% of levels prior to smoking, but there was no increase in 4 control smokers tested before and 1 h after sham smoking. Superoxide production by unstimulated AM decreased significantly 2 minutes after smoking 4 cigarettes but O ₂ ⁻ production by stimulated AM was not affected. Smoking had no effect on O ₂ ⁻ production by AM under the other conditions tested. We conclude that, in addition to the chronic effect of smoking that increases O ₂ ⁻ production by AM, there may be a stimulating effect of acute smoking, depending on the amount smoked and the time after smoking. The increased O ₂ ⁻ production by AM following smoking may be a factor contributing to inactivation of alpha₁-protease inhibitor. Presented in part at the American Thoracic Society Meetings, Miami, May 1984.     

Inhibition of concanavalin A-induced phosphatidylinositol turnover and lysosomal enzyme release by cyclic AMP-elevating agents in rat peritoneal macrophages

When rat peritoneal macrophages were stimulated with concanavalin A (Con A), phosphatidylinositol (PI) turnover was rapidly induced and concomitantly N-acetylglucosaminidase was released. These two reactions were markedly inhibited by prostaglandin E1, which elevated the cellular cyclic AMp levels. This effect was mimicked by dibutyryl cyclic AMP. These results suggest that the elevation of the cellular cyclic AMP levels might play a role in the inhibition of the early stages of Con A-induced activation of macrophages through the inhibition of PI turnover.     

Influence of carbon particles on superoxide and hydrogen peroxide radical release during the killing of Mycobacterium bovis by alveolar macrophages

Setting: Diagnostic bronchoscopy performed on untreated African patients with tuberculosis revealed alveolar macrophages filled with carbon particles. It was postulated that this was the result of excessive inhalation of smoke from domestic fires and the consequent phagocytosis by alveolar macrophages.Objective: To determine whether carbon particles influence the release of superoxide and hydrogen peroxide radicals by the alveolar macrophage during killing of Mycobacterium bovis.Design: Alveolar macrophages were recovered by bronchoalveolar lavage from adult rabbits and cultured. Experimental macrophages were exposed to M. bovis and carbon particles, controls only to M. bovis. Superoxide release was measured by the superoxide dependent cytochrome C reduction method and hydrogen peroxide release by luminol dependent chemiluminescence. Significance of differences was calculated by Student's t-test for unpaired data.Results: For superoxide and hydrogen peroxide release, results show a significant difference between the experiments and the controls. Hydrogen peroxide radicals are, however, released at a low constant average median value in the controls.Conclusion: Hydrogen peroxide is not greatly involved in the killing of M. bovis by alveolar macrophages since low concentrations are released in the controls. Ingestion of large amounts of carbon particles decreases the release of superoxide and hydrogen peroxide radicals.     

Interleukin-6 release by rat liver macrophages

Tissue macrophages of the liver (Kupffer cells) release interleukin-6 (IL-6) in vitro. Since Kupffer cells reside in close proximity to hepatocytes, which are major target cells of IL-6, the regulation of IL-6 release by hepatic macrophages has been investigated in this study. Using the hybridoma growth test to detect IL-6, we found that Kupffer cells already maximally release IL-6 at endotoxin concentrations as low as 1.0 ng/ml. The stimulated secretion of IL-6 was increased 4-8-fold by endotoxin when compared to the control macrophages incubated in serum-containing medium alone. The preincubation of macrophages with interferon-gamma enhanced the capacity of Kupffer cells to respond to endotoxin. The secretion of IL-6 could also be induced by interleukin (IL)-1 beta and tumor necrosis factor (TNF-alpha). The most potent inducers, however, were the paramyxoviruses Newcastle Disease Virus and Sendai Virus. The release of IL-6 by macrophages upon stimulation with endotoxin was almost completely inhibited by 1 microM dexamethasone. Whereas 100 nM of prostaglandin E2 (PGE2) inhibited the release of TNF-alpha in rat Kupffer cells, it did not affect the secretion of IL-6.     

Macrolide antibiotics inhibit nitric oxide generation by rat pulmonary alveolar macrophages.

There is evidence that macrolide antibiotics are effective in the treatment of chronic airway inflammatory diseases, probably through actions other than their antibacterial properties. In order to determine whether macrolides affect the nitric oxide-generating system in the respiratory tract, rat pulmonary alveolar macrophages (PAMs) were studied in vitro. The release of NO was assessed by direct measurement with a specific amperometric sensor for this molecule, and the expression of type II NO synthase (NOS) messenger ribonucleic acid (mRNA) was determined by Northern blotting. Incubation of PAMs with lipopolysaccharide from Escherichia coli and recombinant human interferon-gamma caused release of NO, which was accompanied by induction of type II NOS mRNA. The release of NO was reduced by coincubation of cells with the macrolides erythromycin, clarithromycin and josamycin in a concentration-dependent manner, the maximal inhibition being 73+/-10, 81+/-6 and 84+/-9%, respectively, but was not altered by amoxycillin or cefaclor. These macrolides likewise inhibited the induction of type II NOS mRNA, whereas no inhibitory effects were observed with amoxycillin or cefaclor. These results suggest that macrolide antibiotics specifically inhibit type II NO synthase gene expression and consequently reduce NO production by rat pulmonary alveolar macrophages, which might result in attenuation of airway inflammation.     

Production of reactive oxygen species by rat alveolar macrophages. Dissociation between the intracellular and extracellular release of hydrogen peroxide]

In order to clarify the features of reactive oxygen species produced by rat alveolar macrophages (AMs), the concentrations of intracellular and extracellular hydrogen peroxide were measured under various experimental conditions. Intracellular hydrogen peroxide was measured by DCFH method using a flow cytometer, while the extracellularly released fraction was measured by scopoletin method using a spectrophotometer. The concentration of intracellular hydrogen peroxide after stimulation with opsonized zymosan (10 micrograms/ml) was significantly higher than that after stimulation with phorbol myristate acetate (PMA; 100 ng/ml). On the other hand, hydrogen peroxide released extracellularly after stimulation with PMA was significantly greater that that after stimulation with opsonized zymosan. These results indicate that the soluble membrane stimulant and the phagocytic particles have different mechanisms in activating the production of hydrogen peroxide in AMs. That is, hydrogen peroxide induced by PMA was mainly released extracellularly, while that induced by zymosan was mainly released into the intracellular environment. At rest, the concentration of intracellular hydrogen peroxide in rat AMs was high. Potassium cyanate, a known mitochondrial inhibitor, suppressed the intracellular hydrogen peroxide in AMs not only at rest but also after stimulations, indicating that most of the reactive oxygen species released into the intracellular environment in AM are produced by mitochondria. From these results, in order to gain a closer insight into the function of AMs, it is very important to distinguish the oxidative metabolites produced intracellularly which are related to bactericidal function from those of the extracellularly released fraction which give rise to lung damage.     

Subclinical alveolar inflammation in rheumatoid arthritis: superoxide anion, neutrophil chemotactic activity and fibronectin generation by alveolar macrophages

Interstitial lung disease (ILD) can be detected by pulmonary function testing (PFT) in 30-40% of rheumatoid arthritis (RA) patients. We assessed by bronchoalveolar lavage (BAL) the patterns of alveolitis in 21 RA patients: group 1 comprised 12 patients without evidence of ILD, and group 29 patients with clinical ILD defined by abnormal pulmonary function tests and/or chest X-ray. Cellular characteristics of BAL were studied in both groups. In addition, alveolar macrophages (AM) from patients in group 1 were isolated, and three parameters of cellular activation were studied: superoxide anion, fibronectin and neutrophil chemotactic activity generation. Total cell counts were not increased in group 1 but significantly increased in group 2 compared to controls. In group 1, 5/12 patients had elevated lymphocyte percentage (greater than 18%) suggesting subclinical lymphocyte alveolitis. In contrast, neutrophil alveolitis (greater than 4%) was found in 7/9 patients in group 2, mean percentage 12.9 +/- 4.2, compared with 1.2 +/- 6.4% in controls and 1.9 +/- 0.5% in group 1. These changes were not correlated with disease duration nor rheumatoid factor titres. Marked elevation of lymphocyte percentage was observed in patients with abnormal serum beta-2-microglobulin. Alveolar macrophages from group 1 patients released increased amounts of superoxide anion (7260 +/- 2700 vs controls 850 +/- 120 URL/5.10(5) cells), neutrophil chemotactic activity (21 +/- 4.8 vs controls 8.1 +/- 0.7 cells/HPF), and fibronectin (6.1 +/- 1.6 vs controls 1.3 +/- 0.2 ng.10(6) cells/hour). Whether or not lymphocyte alveolitis and/or AM dysfunction are pathogenic mechanisms of subsequent interstitial lung disease in patients who are still free of symptoms remains to be determined.     

Iprindole-induced phospholipidosis in rat alveolar macrophages: alterations in oxygen consumption and release of oxidants

Rats chronically treated with the cationic amphipilic drug iprindole developed a phospholipid storage disorder in their pulmonary alveolar macrophages (AMs). AMs from these iprindole-treated rats (IP-AMs) were compared to AMs from control rats (C-AMs) regarding oxygen consumption and the release of two reactive oxygen species, superoxide anion and hydrogen peroxide. Responses of C-AMs and IP-AMs were compared at rest and when stimulated by unopsonized or opsonized zymosan. Opsonization was not necessary in order to induce respiratory burst-associated phenomena in either cell type; in fact in all cases, for given cell type responses to unopsonized zymosan were virtually identical to those of opsonized zymosan. When at rest, IP-AMs consumed oxygen at a rate nearly identical to that of C-AMs. When stimulated with zymosan particles, IP-AMs consumed more oxygen than controls. However, when superoxide anion and hydrogen peroxide, two products of the respiratory burst were measured, IP-AMs released less of these species than C-AMs when at rest and when particle stimulated. Despite the lower total release of these species by the IP-AMs, the zymosan-induced release (stimulated minus resting levels) was greater for these cells than C-AMs. Therefore, the IP-AMs were found to be more responsive to the zymosan particle than C-AMs. The results indicate marked changes in the release of reactive oxygen species from the AMs following induction of phospholipidosis.     

Tumor killing by human alveolar macrophages and blood monocytes. Decreased cytotoxicity of human alveolar macrophages

Tumor killing by human alveolar macrophages (AM) might be an important mechanism of pulmonary defense against neoplastic disease. We compared AM and blood monocytes (Mo) for the ability to kill 2 neoplastic targets, A549 human lung adenocarcinoma cells and P815 mastocytoma cells. Blood monocytes were able to kill both targets, whereas AM killed neither. Tumor killing by Mo was spontaneous and was not increased by incubation with lipopolysaccharide. Because the P815 target is highly sensitive to lysis by hydrogen peroxide (H2O2), it afforded the opportunity to compare AM and Mo for the ability to kill tumors by the production of toxic oxygen compounds. Comparable amounts of superoxide anion were produced by AM and Mo after stimulation with phorbol myristate acetate. However, luminol-enhanced chemiluminescence of AM was far less than that of Mo, suggesting that AM could not utilize the myeloperoxidase-H2O2-halide ion system for tumor killing. The addition of exogenous peroxidase to cultures of AM and P815 cells enabled AM to kill this tumor cell. Our results suggest that as Mo mature into AM, their ability to kill tumor cells declines and that AM may be unable to kill H2O2-sensitive tumors because of a loss of myeloperoxidase during maturation.     

Morphometric comparisons of rat alveolar macrophages, pulmonary interstitial macrophages, and blood monocytes.

Pulmonary interstitial macrophages (IM) account for a substantial fraction of the total pulmonary macrophage (PM) population in the mammalian lung, with the remaining balance of extravascular mononuclear phagocytes being mainly alveolar macrophages (AM). Unlike the AM that can be harvested readily by bronchoalveolar lavage, the lung's IM subpopulation of PM has been characterized less well, primarily because of its relative inaccessibility. Recently we developed a method to isolate viable IM from rat lungs using an Fc gamma receptor affinity technique in conjunction with multiparameter flow cytometry. Using this approach, we undertook the present investigation to characterize quantitatively the structural features of the IM and to compare the morphologic attributes of this subpopulation of PM to those of flow cytometrically sorted AM and blood monocytes (BM). Measured or calculated parameters for each population included mean cellular equivalent circular diameter, cell area and volume, and nuclear, mitochondrial, cytoplasmic, and lysosomal volume densities in each cell type. Lysosomal volume densities were subcategorized further into primary lysosomes, small secondary lysosomes, large secondary lysosomes, lipid droplets, and vacuoles. Additionally, the shape, form, and surface irregularity of the cells and various subcellular components were determined. Comparisons of the size and other structural features of the AM, IM, and BM have indicated that (1) the morphologic phenotypes of these three populations of mononuclear phagocytes distinctly differ from one another, (2) the IM and BM are morphologically and morphometrically more akin to one another than they are to AM, and (3) the IM are more similar to the AM than are the BM. These findings suggest that the IM may represent a transitional stage of maturation between BM and AM. Our findings, however, do not rule out the possibility that at least some of the lung's IM are a discrete, BM-independent population of macrophages.     

己酮可可碱对肺结节病患者肺泡巨噬细胞释放细胞因子的作用

目的　研究己酮可可碱 (POF)对肺结节病患者肺泡巨噬细胞 (AM)产生细胞因子的作用 ,并与地塞米松 (DEX)的作用相比较。方法　收集 1 4例活动期肺结节病患者的AM ,以 1 0 %RPMI为培养液 (含有 1 0 %热灭活胎牛血清、2mmol/LL 谷氨酰胺、2 0 0kU/L青霉素及 2 0 0mg/L链霉素 ) ;或1 0 %RPMI加内毒素 (LPS ,1 0 0 μg/L) ;或分别加入浓度为 0 0 1mmol/L、0 1mmol/L和1mmol/L的POF ;或加入 0 1mmol/LDEX进行AM培养 2 4h。用酶联免疫吸附 (ELISA)法测定培养上清液中细胞因子含量。结果　POF对结节病患者AM自发释放的肿瘤坏死因子α(TNF α)有剂量依赖性抑制作用 (P <0 0 0 1 ) ,而对其他自发释放的细胞因子无影响。 0 1mmol/LDEX抑制自发释放的TNF α、可溶性肿瘤坏死因子受体 (sTNFR 2 )、白细胞介素 (IL) 1 β和IL 1 0 (P <0 0 0 1或 <0 0 5 或 <0 0 1 )。除sTNFR 1外 ,POF亦抑制这些由LPS刺激的AM释放的细胞因子 (P <0 0 5或 <0 0 0 1 )。与POF相似 ,0 1mmol/LDEX同样抑制这些LPS刺激的细胞因子释放 (P <0 0 5或 <0 0 0 1 ) ,但对sTNFR 1和IL 1 β无影响。 结论　与DEX相比 ,POF有更宽的治疗窗。用在结节病治疗上可以减少皮质激素用量或可将其替代。然而POF治疗结节病及其他肺部疾病的临床价     

Prostaglandin synthesis and release by subpopulations of rat interstitial macrophages

Recent data indicate that interstitial macrophages are not functionally homogeneous, but are heterogeneous with several subpopulations that differ both morphologically and functionally. Furthermore, interstitial macrophages are believed to be precursor to alveolar macrophages, which have recently been shown to be heterogeneous in their ability to synthesize and release prostaglandins. Considering the apparent importance of prostaglandin synthesis and release in inflammatory and immune responses, the current study was undertaken to determine if interstitial macrophage subpopulations differ in their ability to synthesize and release prostaglandin (PG) E, PGI2, and thromboxane (Tx) A2 after stimulation by calcium ionophore A23187, zymosan, or aggregated IgG. Interstitial macrophages were harvested and separated into 18 density-defined fractions. Density-defined interstitial macrophages (DD-IM) showed marked heterogeneity in prostaglandin synthesis and release. Maximal PGE synthesis and release was seen as a single broad peak after calcium ionophore A23187 and zymosan stimulation. In contrast, no peak in PGE synthesis was seen after aggregated IgG stimulation. PGI2 synthesis also was seen as a single broad peak generated by the lower density interstitial macrophage subpopulations after all stimuli. Similarly, TxA2 synthesis and release was maximal from a broad range of various DD-IM after calcium ionophore A23187, zymosan, and aggregated IgG stimulation. Furthermore, the synthesis and release of TxA2 correlated with the presence of zymosan and IgG receptors on DD-IM. The results demonstrate that DD-IM are heterogeneous in ability to synthesize and release prostaglandins, which are dependent on the stimuli.     

Hydrogen peroxide release from alveolar macrophages and alveolar type II cells during adaptation to hyperoxia in vivo.

The effect of hyperoxia (1-14 days, 85% O2) on rat alveolar macrophage and alveolar type II cell oxidant and antioxidant characteristics was investigated. Unstimulated control macrophages (2 h ex vivo) released hydrogen peroxide at a rate of 3.5 +/- 1.3 nmol/min mg protein-1, which was a cyanide-sensitive process. H2O2 release from alveolar macrophages decreased slightly but not significantly after 1 day in hyperoxia and increased significantly after 3 days (180%, p less than .05) and 14 days (380%, p less than .01). When H2O2 release was expressed as nmol from total macrophages per animal, the increase after 14 days in hyperoxia was 760%. H2O2 generation by hyperoxic macrophages was cyanide resistant, indicating the involvement of active NADPH oxidase. In both control and hyperoxic macrophages H2O2 release could be significantly stimulated with phorbol myristate acetate (PMA). Comparisons of H2O2 release by freshly isolated alveolar macrophages and alveolar type II cells must be cautiously interpreted because some cell functions may change during the isolation procedure. Freshly isolated (6 h ex vivo) control alveolar type II cells were found to generate H2O2 at a rate of 0.26 +/- 0.05 nmol/min mg protein-1. In type II cells H2O2 release, calculated as nmol/mg protein, decreased during the first 7 days of hyperoxia to 10% (p less than .01) of the control value and then returned back up to the control level after 14 days. A similar decrease was observed if H2O2 release was calculated as nmol/cell number. H2O2 release from control and hyperoxic type II cells was cyanide sensitive. The decrease in H2O2 release in type II cells was associated with cell membrane injury (as assessed by electron microscopy), while biochemical markers of cellular injury (trypan blue exclusion and cellular high-energy phosphates ATP, ADP) were unchanged. The ability of type II cells to scavenge extracellular H2O2 did not change in acute hyperoxia, but it increased significantly during the second week in hyperoxia. These results indicate that macrophages but not type II cells are stimulated to produce H2O2 during prolonged exposure to hyperoxia.     

Effect of aging on nitric oxide production by rat alveolar macrophages

Nitric oxide (NO) plays an important role in alveolar macrophages (AM)-mediated defense against infection. The elderly become highly susceptible to respiratory tract infection. Inhibition of NO production significantly suppresses defense against infections. Therefore, it is necessary to elucidate the effect of senescence on NO production of AM. The alveolar microenvironment and lymphocytes affect NO production by AM. We examined whether changes in the alveolar microenvironment, lymphocytes, or AM brought about by aging affect NO production by AM. Bronchoalveolar lavage fluid was used as a substitute for the alveolar microenvironment. The results showed that NO production by AM activated by lymph node cells in bronchoalveolar lavage fluid from old rats in response to concanavalin A decreased compared with that of young rats. AM from aged rats produced less NO than AM from young rats. Bronchoalveolar lavage fluid and lymph node cells from aged rats had no effect on the amount of NO produced by AM. Therefore, age-associated decrease in the functional capacity of AM plays a central role in the decrease of NO production.     

In vivo initiation of unstimulated in vitro interleukin-1 release by alveolar macrophages

Alveolar macrophages (AM) can be stimulated in vitro with material such as lipopolysaccharide, and this activation releases cytokines, collectively called interleukin-1, that can stimulate local cells such as fibroblasts, systemic cells such as lymphocytes, and/or distant parenchymal cells such as hepatocytes. During murine infection with the nematode Nippostrongylus brasiliensis, AM are activated as the parasite larvae migrate through the lung. We examined AM for unstimulated release of lymphocyte-activating factor (LAF) and hepatocyte-stimulating factor (HSF) as evidence of in vivo activation. Two days after infection, marked unstimulated release of LAF was demonstrated along with a smaller increase in unstimulated release of HSF activity. Release of both activities could be further augmented by in vitro stimulation with lipopolysaccharide. Eight days after infection unstimulated HSF activity was even higher than on Day 2, whereas unstimulated LAF release returned to normal. These findings suggest that a natural infective process causes activation of the resident AM population, resulting in release of potent immune and inflammatory-modulating cytokines in situ and that AM play a crucial role in the initiation of host defense and repair responses to infection.     

Direct measurement of hydrogen peroxide release from rat alveolar macrophages: artifactual effect of horseradish peroxidase

Investigators disagree on the amount of hydrogen peroxide (H2O2) released by resting and stimulated alveolar macrophages. The method commonly used to measure H2O2 release involves horseradish peroxidase (HRP)-catalyzed oxidation of scopoletin by H2O2. We describe an artifact in this method that may explain the seemingly inconsistent data reported by other investigators. Release of H2O2 and luminol-catalyzed chemiluminescence are stimulated in rat alveolar macrophages by type II HRP at concentrations normally used in the HRP-scopoletin method. The amount of H2O2 released depends upon the length of time the cells are preincubated at 37.5 degrees C and the time at which type II HRP is added. After stimulation with type II HRP, the cells do not release additional H2O2 upon exposure to zymosan particles. Myeloperoxidase, an alternative catalyst to type II HRP, does not stimulate H2O2 release and, therefore, can be used to measure H2O2 release from rat alveolar macrophages. Using myeloperoxidase, resting H2O2 release is negligible; after zymosan stimulation, 6.14 (+/- 0.87) X 10(-6) nmoles/cell X 10 min is released. In addition, more pure HRP preparations (types VI, VII, VIII, and IX) do not stimulate alveolar macrophages to release H2O2 and can be used to monitor zymosan-induced H2O2 release. As our data indicate that type II HRP stimulates H2O2 release from rat and guinea pig alveolar macrophages, it is not the catalyst of choice for this assay. In conclusion, our data explain the conflicting results found in the literature and indicate that rat alveolar macrophages release minimal amounts of H2O2 at rest and can be stimulated by zymosan.