Experimental study of the effect of intraperitoneal heparin on tumour implantation following laparoscopy

BACKGROUND

Conclusions drawn from clinical reports of port site metastases following laparoscopic resection of intra-abdominal malignancy are now supported by a burgeoning experimental literature which suggests that laparoscopy promotes tumour metastasis to wounds. This study investigated the effect of intraperitoneal blood and heparin on the incidence of tumour cell implantation and port site metastasis.

METHODS

Twenty-four Dark Agouti rats underwent laparoscopy with carbon dioxide insufflation and the instillation of a tumour cell suspension and/or blood into the peritoneal cavity. Rats were allocated randomly to one of the following study groups (six rats per group): (1) controls; (2) intraperitoneal blood (2 ml blood introduced from a syngeneic donor rat); (3) intraperitoneal heparin; (4) intraperitoneal blood and heparin. Rats were killed 7 days after the procedure, and the peritoneal cavity and port sites were examined for the presence of tumour.

RESULTS

Tumour implantation and port site metastases were reduced by the intraperitoneal administration of heparin, but increased by the presence of intraperitoneal blood.

CONCLUSION

The results of this study suggest that tumour implantation following laparoscopy is promoted by the presence of intraperitoneal blood and that this effect may be reduced by the use of intraperitoneal heparin.

Cellular immune responses against proinsulin: no evidence for enhanced reactivity in individuals with IDDM

Investigations of humans and nonobese diabetic mice suggest that proinsulin and/or a fragment of the region spanning C-peptide and the B-chain of insulin (i.e., proinsulin peptide) may serve as key autoantigens in IDDM. Therefore, we analyzed cellular immune reactivities against these molecules in people with or at varying risks for the disease to clarify their role in the pathogenesis of IDDM. In vitro peripheral blood mononuclear cell (PBMC) responses against these antigens, a control antigen (tetanus toxoid), and phytohemaglutinin were determined in 60 individuals with newly diagnosed IDDM (< or = 1 day from diagnosis) in 34 islet cell cytoplasmic autoantibody- and/or insulin autoantibody-negative first-degree relatives of the IDDM subjects, and in 28 autoantibody-negative control subjects. Unlike previous reports suggesting diabetes-associated elevations in cellular immunity to other beta-cell antigens (e.g., GAD, IA-2, etc.), we observed equivalent levels of phytohemaglutinin stimulation and cellular proliferation in all groups against these antigens (all P values were not significant). The mean stimulation index +/- SD and frequency of reactivity to proinsulin for healthy control subjects and IDDM patients, respectively, were as follows: 1 microg/ml (1.5 +/- 1.0, 1 out of 17 [6%]; 1.9 +/- 1.4, 4 out of 33 [12%]); 10 microg/ml (1.7 +/- 1.3, 1 out of 17 [6%]; 1.2 +/- 0.6, 0 out of 28 [0%]); and 50 microg/ml (1.2 +/- 0.6, 1 out of 16 [6%]; 1.1 +/- 0.6, 1 out of 27 [4%]). The response in healthy control subjects, autoantibody-negative relatives, and IDDM patients, respectively, against the proinsulin peptide fragment were as follows: 1 microg/ml (0.9 +/- 0.4, 1 out of 12 [8%]; 1.3 +/- 1.1, 4 out of 34 [11%]; 1.1 +/- 0.3, 2 out of 28 [7%]); 10 microg/ml (0.9 +/- 0.6, 1 out of 12 [8%]; 1.2 +/- 0.6, 3 out of 34 [9%] 1.4 +/- 1.7, 2 out of 28 [7%]); and 50 microg/ml (1.0 +/- 0.7, 1 out of 12 [8%]; 1.2 +/- 0.5, 2 out of 34 [6%]; 1.3 +/- 0.5, 2 out of 28 [7%]). Taken together with previous studies reporting relatively infrequent occurrences of autoantibodies to proinsulin, the role of immunity to this molecule in the pathogenesis of IDDM in humans remains unclear.

Influence of cytotoxic agents on intraperitoneal tumor implantation after laparoscopy

PURPOSE

Recent experimental studies suggest that laparoscopic surgery for abdominal malignancy may be associated with increased tumor implantation. This study investigated the influence of cytotoxic agents (administered intraperitoneally or intramuscularly) on implantation of a tumor cell suspension after laparoscopic surgery in an experimental model.

METHODS

Thirty-three Dark Agouti rats underwent laparoscopy with CO2 insufflation and instillation of a tumor cell suspension into the abdominal cavity. Rats were randomly allocated to one of the following study groups (9 rats in the control group, 6 rats in all other groups): 1) control (no intraperitoneal instillation); 2) intraperitoneal normal saline (0.9 percent); 3) intraperitoneal povidone-iodine (Betadine to normal saline 1:10 dilution); 4) intraperitoneal methotrexate (2 doses of 0.125 mg/kg body weight in normal saline administered 24 hours apart); 5) intramuscular injection of 2 doses of 0.125 mg/kg body weight administered 24 hours apart (no intraperitoneal agent). Rats were killed 7 days after the procedure, and the peritoneal cavity and port sites were examined for the presence of tumor.

RESULTS

A significant reduction in tumor implantation and port-site metastases was observed in all treatment groups (povidone-iodine and intramuscular and intraperitoneal methotrexate).

CONCLUSIONS

This study suggests that tumor implantation after laparoscopic surgery and port-site metastases might be prevented by the intraperitoneal or systemic administration of cytotoxic agents. Further studies are needed to determine whether these findings can be applied to clinical practice.

Sustained secretion of human alpha-1-antitrypsin from murine muscle transduced with adeno-associated virus vectors

Recombinant adeno-associated virus (AAV) vectors have been used to transduce murine skeletal muscle as a platform for secretion of therapeutic proteins. The utility of this approach for treating alpha-1-antitrypsin (AAT) deficiency was tested in murine myocytes in vitro and in vivo. AAV vectors expressing the human AAT gene from either the cytomegalovirus (CMV) promoter (AAV-C-AT) or the human elongation factor 1-alpha promoter (AAV-E-AT) were examined. In vitro in C2C12 murine myoblasts, the expression levels in transient transfections were similar between the two vectors. One month after transduction, however, the human elongation factor 1 promoter mediated 10-fold higher stable human AAT expression than the CMV promoter. In vivo transduction was performed by injecting doses of up to 1.4 x 10(13) particles into skeletal muscles of several mouse strains (C57BL/6, BALB/c, and SCID). In vivo, the CMV vector mediated higher levels of expression, with sustained serum levels over 800 micrograms/ml in SCID and over 400 micrograms/ml in C57BL/6 mice. These serum concentrations are 100,000-fold higher than those previously observed with AAV vectors in muscle and are at levels which would be therapeutic if achieved in humans. High level expression was delayed for several weeks but was sustained for over 15 wk. Immune responses were dependent upon the mouse strain and the vector dosage. These data suggest that recombinant AAV vector transduction of skeletal muscle could provide a means for replacing AAT or other essential serum proteins but that immune responses may be elicited under certain conditions.

Tumor implantation following laparoscopy using different insufflation gases

BACKGROUND

Laparoscopic manipulation of malignancies is associated with an increased incidence of metastasis to port sites in experimental models. This study investigated the effect of different insufflation gases on the implantation of a tumor cell suspension following laparoscopic surgery in an established small animal model.

METHODS

Forty Dark Agouti rats underwent laparoscopy and the introduction into the peritoneal cavity of a tumor cell suspension. The insufflating gas used for each procedure was one of the following gases (10 rats in each group): carbon dioxide (CO2), nitrous oxide (N2O), helium, and air. The rats were killed 7 days after surgery, and the peritoneal cavity and port sites were examined for the presence of tumor.

RESULTS

Although no significant differences were seen between air, CO2, and N2O insufflation groups, tumor involvement of peritoneal surfaces was less likely following helium insufflation.

CONCLUSION

The results of this study suggest that tumor metastasis to port sites following laparoscopic surgery may be influenced by the choice of insufflation gas. In this study, helium was associated with reduced tumor growth.

Aging and the immune response to tetanus toxoid: diminished frequency and level of cellular immune reactivity to antigenic stimulation

The period of efficacious immune reactivity afforded by tetanus immunization and the need for continuing some forms of tetanus vaccination programs have been the subjects of recent debates. Our studies demonstrate that the level of antitetanus immunity based on immunological memory (i.e., cellular immune responsiveness) varies dramatically as a function of age, with older individuals constituting a population which is increasingly susceptible to tetanus infection.

Illicit alcohol (moonshine) consumption in West Alabama revisited

BACKGROUND

Lacy and Wintemitz in 1984 and Pegues in 1991 showed the presence of moonshine-related lead poisoning in Alabama.

METHODS

This study was a 10-year follow-up to the Lacy and Wintemitz study and used a similar inpatient retrospective chart review methodology. We looked at cases occurring between 1989 and 1992, which were positive for either a history of moonshine consumption or lead intoxication and cases suspicious for the diagnoses, based on the Lacy and Wintemitz epidemiologic parameters.

RESULTS

A declining, yet continuing, presence of moonshine-related lead intoxication still exists in west Alabama.

CONCLUSIONS

The findings suggest the current at-risk patients may continue to be middle-aged to elderly men from rural settings. Furthermore, appropriate screening tests were not always ordered, which suggests a possible lack of awareness of the disorder by care givers.

Efficacy of cytotoxic agents for the prevention of laparoscopic port-site metastases

BACKGROUND

Recent experimental studies support initial clinical impressions that laparoscopic surgery for malignant neoplasms may be associated with an increased incidence of metastases to port sites. This study investigated in an experimental model the influence of cytotoxic agents (administered intraperitoneally or intramuscularly) on the development of port-site metastases following laparoscopic surgery.

METHODS

Seven days after the implantation of an adenocarcinoma in the left abdominal flank, 72 Dark Agouti rats underwent laparoscopy with carbon dioxide insufflation, instillation of an intraperitoneal agent, and intraperitoneal tumor laceration within the following study groups (12 rats in each group): (1) control (no intraperitoneal instillation); (2) intraperitoneal instillation of isotonic sodium chloride solution (0.9%); (3) intraperitoneal instillation of povodine-iodine (1:10 dilution of povidine-iodine and isotonic sodium chloride solution); (4) intraperitoneal instillation of methotrexate (0.125 mg of methotrexate in 3 mL of isotonic sodium chloride solution); and (5) intraperitoneal instillation of aqueous chlorhexidine acetate. Twelve additional rats underwent laparoscopic tumor laceration following intramuscular injection of 0.125 mg of methotrexate (no intraperitoneal agent). Rats were killed 7 days after the procedure, and the wounds were examined histologically by a blinded histopathologist for the presence of tumor metastases.

RESULTS

No tumor was found in any port site following the intraperitoneal administration of povidine-iodine (P=.04). In contrast, port-site metastases developed in the control group (5 [41.7%] of 12), the isotonic sodium chloride solution group (4 [33.3%] of 12), the chlorhexdine group (4 [33.3%] of 12), the intraperitoneal methotrexate group (2 [16.7%] of 12), and the parenteral methotrexate group (5 [41.7%] of 12).

CONCLUSIONS

The results of this study suggest that the development of metastases to port sites following laparoscopic surgery may be prevented by the intraperitoneal instillation of diluted povodine-iodine. Other agents failed to influence the incidence of port-site metastases. Further studies are needed to determine if these findings can be applied to humans.

Wound metastasis after laparoscopy with different insufflation gases

BACKGROUND

There is growing evidence that laparoscopy for malignancy is associated with an increased incidence of metastasis to port sites. This study investigated the effect of different insufflation gases on port-site metastasis after laparoscopy in an established animal model.

METHODS

Forty-eight Dark Agouti rats with an established adenocarcinoma in the left flank underwent laparoscopic intraperitoneal tumor laceration. The gas used for insufflation was one of the following (12 rats in each group): (1) CO2, (2) N2O, (3) helium, or (4) air. Rats were killed 7 days after the procedure, and the port sites were examined for the presence of tumor metastasis.

RESULTS

Tumor involvement of port sites was significantly less likely after helium insufflation than in the other groups (p < 0.0001). There was no significant difference between the air, CO2, and N2O groups.

CONCLUSIONS

This study suggests that the development of metastases in port sites after laparoscopy may be influenced in part by the choice of insufflation gas used to create the pneumoperitoneum. In particular, helium was associated with a reduced rate of metastases.

Evaluation of four DNA typing techniques in epidemiological investigations of bovine tuberculosis

DNA fingerprinting techniques were used to type 273 isolates of Mycobacterium bovis from Australia, Canada, the Republic of Ireland, and Iran. The results of restriction fragment length polymorphism (RFLP) analysis with DNA probes from IS6110, the direct repeat (DR), and the polymorphic GC-rich sequence (PGRS) were compared with those of a new PCR-based method called spacer oligonucleotide typing (spoligotyping) developed for the rapid typing of Mycobacterium tuberculosis (J. Kamerbeek et al., J. Clin. Microbiol. 35:907-914, 1997). Eighty-five percent of the isolates harbored a single copy of IS6110, and 81.5% of these carried IS6110 on the characteristic 1.9-kb restriction fragment. RFLP analysis with IS6110 identified 23 different types, RFLP analysis with the DR probe identified 35 types, RFLP analysis with the PGRS probe identified 77 types, and the spoligotyping method identified 35 types. By combining all results, 99 different strains could be identified. Isolate clusters were frequently associated within herds or were found between herds when epidemiological evidence confirmed animal movements. RFLP analysis with IS6110 was sufficiently sensitive for the typing of isolates with more than three copies of IS6110, but RFLP analysis with the PGRS probe was the most sensitive typing technique for strains with only a single copy of IS6110. Spoligotyping may have advantages for the rapid typing of M. bovis, but it needs to be made more sensitive.

The effect of laparoscopy on the movement of tumor cells and metastasis to surgical wounds

BACKGROUND

A variety of mechanisms have been proposed to explain tumor growth in port sites following laparoscopic cancer surgery. We devised two experimental models to determine whether carbon dioxide (CO2) insufflation during laparoscopic surgery influences the movement of tumor cells and leads to tumor implantation and growth in surgical wounds.

METHODS

Model 1: Viable adenocarcinoma cells were introduced into the upper abdomen of six syngeneic immune-competent rats during laparoscopy with CO2 insufflation; the same procedure was followed for a further six rats during gasless laparoscopy. A length of plastic tubing introduced through the anterolateral aspect of the rats' left lower abdominal wall was used to vent the insufflation gas through the abdomen of a recipient rat for 30 min. After 21 days, the peritoneal cavity and surgical wounds of the recipient rat were examined for implanted tumor. Model 2: A suspension of radiolabeled adenocarcinoma cells was introduced into the upper abdomen of five rats during laparoscopy with CO2 insufflation and an additional five rats during gasless laparoscopy. A length of plastic tubing introduced through the anterolateral aspect of the left lower abdominal flank was used to vent the insufflation gas through phosphate-buffered saline solution. After 30 min, the solution was counted for radioactivity.

RESULTS

Tumor growth occurred at the site of both the insufflation and venting ports in the second rat in five of the six rats from the group undergoing insufflation, but it was found in none of the gasless laparoscopy group (p = 0.015). In the second model, significant transfer of tumor cells to the vented gas occurred only in the rats undergoing laparoscopy with insufflation (median, 2.71% versus 0% of the introduced labeled cells; p = 0.008).

CONCLUSIONS

Carbon dioxide insufflation results in tumor dissemination during laparoscopy, leading to port site metastasis. Gasless laparoscopy may prevent this problem.

Effects of dimethyl sulfoxide on apolipoprotein A-I in the human hepatoma cell line, HepG2

Exposure of HepG2 cells to 1% (v/v) dimethyl sulfoxide (DMSO), an effective free radical scavenger, for 24 h resulted in a 2-fold increase in the levels of apolipoprotein (apo) A-I mRNA and secreted protein, with no significant change in apoA-II, apoB, and apoE mRNA and protein levels. The induction of apoA-I was accompanied by a 50% increase in secreted HDL. Nuclear run-off assays indicated that the transcription rate of the apoA-I gene was also increased 2-fold in DMSO-treated cells. Consistent with nuclear run-off assays, transient transfection experiments, using a series of pGL2-derived luciferase reporter constructs containing the human apoA-I proximal promoter, demonstrated that DMSO treatment increased apoA-I promoter activity 2-fold. We have identified a potential 'antioxidant response element' (ARE) in the apoA-I promoter that may be responsible for the increase in apoA-I transcriptional activity by DMSO. Gel mobility shift assays with an apoA-I-ARE revealed increased levels of a specific protein-DNA complex that formed with nuclear extracts from DMSO-treated cells. The formation of this complex is sequence specific as determined by DNA competition studies. When a copy of the ARE was inserted upstream of the SV40 promoter in a luciferase reporter plasmid, a significant 2-fold induction in luciferase activity was observed in HepG2 cells in the presence of DMSO. In contrast, a plasmid containing a mutated apoA-I-ARE did not confer responsiveness to DMSO treatment. Furthermore, pGL2 (apoA-I-250 mutant ARE), in which point mutations eliminated the ARE in the apoA-I promoter, showed no increase in luciferase activity in response to DMSO. These results implicate protein-DNA interactions at the antioxidant response element region in the transcriptional induction of human apoA-I gene expression by DMSO.

Adverse impact of pneumoperitoneum on intraperitoneal implantation and growth of tumour cell suspension in an experimental model

BACKGROUND

An investigation of the effect of laparoscopy and CO2 pneumoperitoneum on the pattern of tumour implantation and growth in the peritoneal cavity was carried out.

METHODS

A suspension of viable adenocarcinoma cells was introduced into the left upper quadrant of the peritoneal cavity of 36 syngeneic immune-competent rats at laparotomy, laparoscopy with CO2 insufflation, and gasless laparoscopy (12 rats in each group). Six days later the peritoneal cavity and surgical wounds were examined for macroscopic evidence of implanted tumour. The abdominal cavity was divided into sectors and macroscopic tumour implantation was determined for each sector and wound. This was confirmed by histological examination.

RESULTS

While tumour implantation occurred in the vicinity of the tumour suspension introduction site in the laparotomy and gasless laparoscopy groups, implantation occurred throughout the peritoneal cavity, including areas remote to the introduction site, in the laparoscopy with CO2 insufflation group. Tumour growth was more likely in the port wounds of rats undergoing laparoscopy with insufflation than without.

CONCLUSIONS

In this model, CO2 insufflation during laparoscopy resulted in widespread tumour dissemination and implantation, when compared to laparotomy and gasless laparoscopy, supporting the postulate that wound metastasis and tumour spread may be more likely following laparoscopic cancer surgery in humans when CO2 insufflation is used.

Gasless laparoscopy may reduce the risk of port-site metastases following laparascopic tumor surgery

OBJECTIVE

To compare the incidence of port-site metastases in an experimental tumor model following tumor manipulation during laparoscopy aided by conventional insufflation with laparoscopy using a gasless technique.

SETTING

An experimental model applied in a research laboratory.

PARTICIPANTS AND INTERVENTIONS

Malignant tumors were implanted in the abdominal wall of 24 rats. Twelve rats underwent tumor laceration at laparoscopy with carbon dioxide insufflation, and 12 rats underwent the same procedure during gasless laparoscopy achieved by abdominal wall suspension. Rats were killed 1 week later and were examined for evidence of tumor metastases. The surgical wounds were examined microscopically by a histopathologist who was unaware of the operative technique used and the site of origin of the specimens.

MAIN OUTCOME MEASURE

Histologically confirmed tumor metastasis to laparoscopic port wounds.

RESULTS

Growth of the primary tumor was equal in both groups. Wound metastases were less likely in the gasless laparoscopy group (3 of 12 vs 10 of 12; P = .01, Fisher exact test).

CONCLUSION

The use of laparoscopy without gas insufflation may reduce the risk of wound metastasis following laparoscopic surgery for cancer.

Cross-linking of human placenta pi class glutathione S-transferase dimer by chlorambucil

Interaction of chlorambucil and the glutathione-depleted human placenta pi class glutathione S-transferase (pi GST) results in the formation of a complex between the drug and the protein at physiological pH. This complex is not formed in the presence of glutathione or S-hexylglutathione. Molecular mass measurement of the reaction product using matrix-assisted laser desorption mass spectrometry indicates that one molecule of chlorambucil cross-links two subunits of the homodimeric protein. A combination of enzymic proteolysis, high performance liquid chromatography, and mass spectrometry reveals that chlorambucil alkylation occurs at cysteine 47 of one subunit and cysteine 101 of the second subunit. This result supports the idea that conformational changes occur in glutathione-depleted pi GST, which allow the bifunctional tether of chlorambucil to cross-link the two subunits of the protein.

Wound metastases following laparoscopic and open surgery for abdominal cancer in a rat model

The recent application of laparoscopic resection techniques to malignant disease has raised safety concerns due to metastasis to surgical access wounds. The significance and incidence of this problem are controversial. In the present study a rat model, in which an implanted tumour was lacerated, was used to investigate whether application of laparoscopic techniques for malignant abdominal disease leads to an increased risk of tumour dissemination and implantation within the peritoneal cavity, and abdominal wall wounds. Malignant cells were implanted into the abdominal wall of 42 rats, resulting 7 days later in the growth of a tumour measuring 20-25 mm in diameter. There were three control groups: no surgery (n = 6); blunt manipulation of the tumour laparoscopically (n = 6); and blunt manipulation of the tumour at laparotomy (n = 6). Twenty-four rats underwent surgical laceration of the tumour capsule at either laparoscopy (n = 12) or laparotomy (n = 12). All rats were killed 1 week later, and examined for macroscopic evidence of tumour metastasis. The abdominal surgical wounds were excised for independent microscopic examination by a histopathologist. Growth of the primary tumour was greater in rats that had an operation than in unoperated controls, and was greater after laparotomy. However, wound metastases were five times more likely after laparoscopic tumour laceration than after the same procedure through an open incision (ten of 12 rats versus two of 12, P = 0.0033). Wound metastases following laparoscopic tumour manipulation are an important and real problem, with significant implications for the application of laparoscopic techniques to excise malignant disease in humans.

Myelinoclastic diffuse sclerosis presenting as a mass lesion in a child with Turner's syndrome

A rare case of myelinoclastic diffuse sclerosis (MDS), occasionally referred to as Schilder's disease, is reported in a child with Turner's syndrome. The child originally presented with a 3-week history of nausea, vomiting and frontal headaches. Magnetic resonance imaging showed a large, contrast-enhancing, right frontal lobe mass which was ultimately resected uneventfully. Complete laboratory investigations and pathological evaluation of the resected specimen verified the case to be MDS. The clinical presentation, laboratory evaluation, imaging characteristics and diagnosis are discussed in this review of the disease. The importance of including demyelinating diseases in the differential diagnosis for newly discovered mass lesions in the pediatric population is underscored by this case.

Lung injury following exposure of rats to relatively high mass concentrations of nitrogen dioxide

Human inhalation exposures to relatively high mass concentrations of the oxidant gas nitrogen dioxide (NO2) can result in a variety of pulmonary disorders, including life-threatening pulmonary edema, pneumonia, and bronchiolitis obliterans. Inasmuch as most experimental studies to date have examined NO2-induced lung injury following exposures to near ambient or supra-ambient concentrations of NO2, e.g., < or = 50 ppm, little detailed information about the pulmonary injurious responses following the acute inhalation of higher NO2 concentrations that are more commensurate with some actual human exposure conditions is currently available. Described in this report are the results from a series of investigations in which various aspects of the inhalation toxicity of high concentrations of NO2 have been examined in laboratory rats. In the first component of our study, we characterized the kinetic course of development of lung injury following acute exposures to high concentrations of NO2 delivered over varying durations, and we assessed the relative importance of NO2 exposure concentration versus exposure time in producing lung injury. For a given exposure duration, the resulting severity of lung injury was found to generally scale proportionately with inhaled mass concentration, whereas for a given concentration of inhaled NO2, the magnitude of resulting injury was not directly proportional to exposure duration. Moreover, evidence was obtained that indicated exposure concentration is more important than exposure time when high concentrations of NO2 are inhaled. In a second component of our investigation, we assessed the pulmonary injurious response that occurs when NO2 is inhaled during very brief, 'high burst' exposures to very high concentrations of NO2. Such exposures resulted in significant lung injury, with the magnitude of such injury being directly proportional to exposure concentration. Comparisons of results obtained from this and the first component studies additionally revealed that brief exposures to the very high concentrations of NO2 are more hazardous than longer duration exposures to lower concentrations. In a third study series, we examined pre-exposure, exposure, and post-exposure modifiers of NO2-induced lung injury, including dietary taurine, minute ventilation, and post-exposure exercise. Results from these studies indicated: (i) dietary taurine does not protect the rat lung against high concentration NO2 exposure, (ii) the severity of acute lung injury in response to NO2 inhalation is increased by an increase in minute ventilation during exposure, and (iii) the performance of exercise after NO2 exposure can significantly enhance the injurious response to NO2.(ABSTRACT TRUNCATED AT 400 WORDS)