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Environment
Original article
The biological effects of individual-level PM2.5 exposure on systemic immunity and inflammatory response in traffic policemen
  1. Jinzhuo Zhao1,
  2. Zhiyi Gao2,
  3. Zhenyong Tian1,
  4. Yuquan Xie3,
  5. Feng Xin1,
  6. Rongfang Jiang1,
  7. Haidong Kan1,
  8. Weimin Song1
  1. 1Department of Environment Health, the Key Laboratory of Public Health Safety, School of Public Health, Fudan University, Shanghai, China
  2. 2Department of Communicable Disease Control and Prevention, Xuhui Center for Disease Control and Prevention, Shanghai, China
  3. 3Department of Cardiology, Xinhua Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, China
  1. Correspondence to Professor Weimin Song, Department of Environment Health, School of Public Health, the Key Laboratory of Public Health Safety, Fudan University, Ministry of Education. Shanghai 200032, China; wmsong1{at}gmail.com

Abstract

Background Ambient fine-particle particulate matter (PM2.5) exposure is associated with the decline in pulmonary function, prevalence of coronary heart disease and incidence of myocardial infarction. The study is to observe the effects of ambient PM2.5 on the cardiovascular system and to explore the potential inflammatory and immune mechanisms.

Methods The subjects included 110 traffic policemen in Shanghai, China, who were aged 25–55 years. Two-times continuous 24 h individual-level PM2.5 measurements were performed in winter and summer, respectively. The inflammatory marker (high-sensitivity C-reactive protein, hs-CRP), immune parameters (IgA, IgG, IgM and IgE) and lymphocyte profiles (CD4 T cells, CD8 T cells, CD4/CD8 T cells) were measured in blood. The associations between individual-level PM2.5 and inflammatory marker and immune parameters were analysed by multiple linear regression.

Results The average concentration of 24 h personal PM2.5 for participants was 116.98 μg/m3 and 86.48 μg/m3 in winter and summer, respectively. In the main analysis, PM2.5 exposure is associated with the increases in hs-CRP of 1.1%, IgG of 6.7%, IgM of 11.2% and IgE of 3.3% in participants, and decreases in IgA of 4.7% and CD8 of 0.7%, whereas we found no statistical association in CD4 T cells and CD4/CD8 T cells. In the adjusted model, the results showed that the increase of PM2.5 was associated with the changes of inflammatory markers and immune markers both in winter and summer.

Conclusions Traffic policeman have been a high-risk group suffering inflammatory response or immune injury because of the high exposure to PM2.5. These findings provided new insight into the mechanisms linking ambient PM2.5 and inflammatory and immune response.

https://doi.org/10.1136/oemed-2012-100864

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    What this paper adds

    • The results indicated that traffic policemen's exposure to high levels of PM2.5 was associated with systemic inflammatory response and immune injury.

    • Inflammatory and immune response might be the mechanisms of cardiovascular injury induced by fine particles.

    • Hs-CRP, immune parameters and lymphocyte profiles are important markers in exploring the PM2.5-induced cardiovascular injury.

    Introduction

    Traffic is one of the major sources of environmental pollution in metropolitan areas. Traffic-generated particulate matter (PM) is the major source of ambient PM. Exposure to ambient PM, especially PM2.5, increases cases of deaths1 and hospitalisation for cardiopulmonary diseases.2 ,3 Its adverse effects have been associated with both short- and long-term exposure.4 ,5 However, the mechanisms of the effects of PM2.5 on cardiovascular diseases remain unclear, and epidemiologic evidence regarding cardiovascular risk at the individual level due to PM2.5 is more limited, especially with regard to dose-response relationship and the effects of individual-level PM2.5 exposure. Potential mechanisms for PM-associated changes in cardiopulmonary diseases have been suggested to include increase in oxidative stress,6 inflammation,7 autonomic modulation impairment8 ,9 and blood coagulation.10 ,11 In our previous experimental study, PM2.5 caused significant changes of indicators associated with cardiovascular injury, such as inflammation, endothelial dysfunction, coagulation disorder and immune injury.12 ,13 Systemic inflammation and immune injury are closely associated with cardiovascular disease. Recent research indicated that the developing immune system is a remarkably sensitive toxicological target for environmental chemicals.14 There is growing evidence that exposure to immunotoxic compounds may not only cause immunosuppression, but also result in increased expression of aberrant immune responses. PM can act directly on many effector cells, such as lymphocytes, monocytes and macrophages which are closely associated with immune and inflammatory response.15 Similarly, ambient PM pollution may influence allergic,16 immunologic17 and systemic inflammatory responses.18 ,19 These evidences support that inflammatory response and immune injury are potentially associated with increased risk of incident coronary heart disease, sudden cardiac death and all-cause mortality.

    High levels of high-sensitivity C-reactive protein (hs-CRP) are independent predictors of cardiovascular disease20 ,21 and may also act as mediators in the pathogenesis of atherosclerosis due to air pollution.22 It has been shown that increased levels of CRP resulting from exposure to PM are involved in the infiltration of monocytes into the arterial wall,23 which promotes atherogenesis by amplifying inflammatory and procoagulant responses.24 In addition, a European study was conducted to evaluate the relationship between PM and a panel of immune biomarkers (total T cells, CD4 cells, CD8 cells, IgG, IgM, IgA and IgE) in children, suggesting that long-term exposure to airborne particulates leads to inflammation of the airways and activation of the cellular and humoral immune system.25 Consequently, these experimental and epidemiological studies suggested that the hs-PCR as marker for inflammatory response, and CD4 cells, CD8 cells, IgG, IgM, IgA and IgE as markers for immune response have important significance in exploring the association between ambient PM2.5 and inflammatory and immune response.

    Recently, most epidemiological studies assessed the PM2.5 exposure using the data of monitoring sites other than individual-level PM2.5.26–28 Only few studies monitored individual-level PM2.5 to explore the effects of PM2.5 on cardiovascular disease,29 which reported the association between PM2.5 exposures and immediate impairment of cardiac autonomic modulation by estimating 24 h individual-level real-time PM2.5 exposures.29 Other studies measured the individual levels of environmental tobacco smoke (ETS) using personal monitors, suggesting that subjects with different induction of CYP1A1 expression in CYP1A1*2A and CYP1A1*2A/*2B carriers may have increased susceptibility to the genotoxic effects of ETS.30

    Traffic policemen, taxi drivers, postmen and traffic wardens were considered the most highly exposed to traffic pollution in cities.31–34 Previous studies conducted in Italy comparing 68 traffic policemen and 62 control subjects (all male) at rest and during a symptom-limited incremental exercise test, suggest that long-term occupational exposure to urban pollutants reduces resistance to physical effort and increases the risk of cardiovascular and respiratory effects.33 In the present study, we examined the individual-level PM2.5 for traffic policemen to assess the association between ambient PM2.5 and systemic inflammatory marker and immune response, and to focus on biological markers of cardiovascular disease for earlier diagnosis and treatment.

    Methods

    Study population and design

    The project was conducted from 2009 to 2010 and included 110 male traffic policemen 25–55 years of age from Shanghai, China. The participants were non-smokers and had no cardiopulmonary disease, as well as currently not under any medications. The participants mainly worked at crossroads to guide the traffic or deal with traffic accidents. Their normal working time was about 8 h during a working day. The study was carried out over one summer period (May 2009–August 2009) and one winter period (November 2009–February 2010). It was approved by the Human Studies Review Committee of the Foundation of School of Public Health, Fudan University. We explained the purpose of the project to all participants and they signed an informed consent form in accordance with the relevant provisions of the Helsinki Declaration. All participants declared that they had not smoked tobacco for at least 6 months prior to their participation. All participants completed a personal history questionnaire including sociodemographic characteristics, lifestyle factors and medical history. We classified education according to the International Standard Classification of Education as total years of formal education. Four categories were defined with the highest category of ≥18 years of education (equivalent to a university degree), and the lowest category of ≤12 years (equivalent to a basic school degree and no vocational training). Regular alcohol intake was defined as any alcohol consumption at least 4–6 days per week. The hours of exposure to vehicle exhaust was defined as weekly working hours.

    Personal exposure monitoring and sample collection

    A portable Air Sampler (Gilian, GilAir-3, USA) was used in combination with a PM2.5 size-selective inlet driven by a 1.5 l/min pump to obtain the personal 24 h mean PM2.5 exposure estimates. A sampling plastic tube was connected with an inlet port and placed at a height which was at the same height of breathing, so that it would represent the individual's actual exposure. The duration was from 8:00 of one day, to 8:00 of the next day. The next morning after the participants finished the 24 h personal PM2.5 monitor, the Air Sampler was returned and the filters were removed from the cassettes and the samples were analysed. All subjects were monitored and sampled twice, once during a summer period and again during the following winter period. The blood samples were collected for hs-CRP and immune markers detection. At the end of the study, the participants answered a recall questionnaire. Five participants who failed to come for the summer collection period and four participants' samples or questionnaire were incomplete, thus leaving 101 samples.

    Marker of inflammation

    In terms of marker of inflammation, we measured high-sensitivity (hs)-CRP using a two-site chemiluminescent enzyme immunometric assay (IMMULITE hsCRP; Diagnostic Stago Corp, California, USA). All analyses were performed in the Zhongshan Hospital, Fudan University.

    Immune markers detection

    CD4 T cells, CD8 T cells, IgA, IgM, IgG and IgE in blood were measured by ELISA (Hengda Baisheng Biological Technology Co, Ltd, China). The assay was performed exactly according to the manufacturer's instructions. The CD4/CD8 T cells were calculated using the values of CD4 T cells and CD8 T cells.

    Statistical analysis

    The entire study population consists of 101 participants. We performed analyses on the participants for whom measurements of biomarkers and complete information on covariates were available (n=101).

    For statistical analysis, the differences of individual-level PM2.5 and biomarker levels between winter and summer were analysed using a paired t test. To assess the short-term association between individual-level PM2.5 and inflammatory and immune markers, we performed multiple linear regression analyses with hs-CRP, IgA, IgM, IgG, IgE, CD4 T cells, CD8 T cells and CD4 T/CD8 T cells as the dependent variables, respectively. We entered the individual-level PM2.5 as independent variables, after adjustment with all confounding factors, such as body mass index (BMI), categorised educational time period, weekly working hours, categorised alcohol intake and season and so on; the association between PM2.5 and inflammatory and immune response was investigated in the main analysis. Then the adjusted model was established to analyse the effects of PM2.5 on inflammatory and immune response in winter and summer.

    Results

    Distribution of personal PM2.5 exposure for 101 participants

    We merged the two periods of personal PM2.5 (n=202) to analyse its distribution. The average concentration of PM2.5 was 101.73 μg/m3 (range, 10.90–217.95 μg/m3). Meanwhile, the summer and winter concentrations and distributions of personal PM2.5 for 101 participants were analysed. The personal PM2.5 concentrations were 116.98 μg/m3 (range, 32.69–217.95 μg/m3) and 86.48 μg/m3 (range, 10.90–185.26 μg/m3) in winter and summer, respectively (table 1). The distribution of individual-level PM2.5 concentration for 101 participants is shown in figure 1. The individual-level PM2.5 concentration was divided into seven groups. The lower bound of the PM2.5 concentration was 35 μg/m3, which was set according to the American Air Quality standards (24 h averaging time, PM2.5, 35 μg/m3). Figure 1 showed that most participants were exposed to 35–175 μg/m3 of PM2.5. Meanwhile, it was found that participants were exposed to higher concentration of PM2.5 in winter when compared with summer.

    View this table:
    Table 1

    Personal PM2.5 exposure in traffic policemen in winter and summer

    Figure 1
    Figure 1

    Distribution of personal particulate matter (PM)2.5 exposure for 101 participants in winter and summer. The distribution was divided into seven categories according to a progressive increase as 35 μg/m3 of PM2.5 every category.

    Descriptive statistics of the study population

    Table 2 describes the statistics of the study population. The participants included in the analysis (n=101) excluding those (n=9) whose personal characteristics or samples were incomplete. We merged the two-period data to describe the study population. The differences of inflammatory markers, lymphocyte profiles and immune parameters corresponding to different PM2.5 levels were observed. The median Hs-CRP was 7.5 μg/ml when PM2.5 was in excess of 175 μg/m3. Meanwhile, median IgM, IgA and IgE increased with the increase of PM2.5, whereas CD4 T cells and CD8 T cells decreased with the increase of PM2.5. Moreover, figure 2 shows that the means of hs-CRP, IgM and IgG for participants were higher in participants in winter than those in summer, whereas CD4 T cells, CD8 T cells and CD4 T/CD8 T cells were lower in winter than those in summer. Meanwhile, we found that there were no distinct differences of IgA and IgE between winter and summer. Thus, it appears that the effects of PM2.5 on inflammatory and immune response might be different between winter and summer.

    View this table:
    Table 2

    Descriptive statistics of the study population (n=202)

    Figure 2
    Figure 2

    The levels of biomarkers related inflammation and immune in participants in winter and summer. The differences of hs-C-reactive protein (A), CD4 T cells, CD8 T cells, IgA, IgG, IgM, IgE (B) and CD4/CD8 T cells (C) between winter and summer were analysed using a paired t test. Data are expressed as mean±SD. **p <0.01, *p <0.05 vs summer.

    Association between personal PM2.5 exposure and immune and inflammatory response

    In the main analysis model, the effects of PM2.5 on inflammatory and immune response were evaluated after controlling for the season, BMI, categorised educational time period, regular alcohol intake and weekly working hours (table 3). The results showed that the increase of PM2.5 was associated with the increases of hs-CRP, IgM, IgG and IgE and the decrease of CD8 and IgA. The increase in PM2.5 was associated with increase in hs-CRP of 1.1% (95% CI 0.6% to 1.5%), IgM of 11.2% (95% CI 10.9% to 11.6%), IgG of 6.7% (95% CI 6.4% to 7.1%) and IgE of 3.3% (95% CI 3.0% to 3.6%), respectively. However, the increase in PM2.5 was associated with a decrease in IgA of 4.7% (95% CI −5.6% to −4.2%) and CD8 T cells of −0.7% (95% CI −1.1% to −0.3%). Meanwhile, we established the adjusted model according to winter and summer. After adjusting for confounding factors, such as BMI, categorised educational time period, regular alcohol intake and weekly working hours, we observed an association of personal PM2.5 with the inflammatory mediators hs-CRP and immune markers IgA, IgM, IgG, IgE, CD4 T cells, CD8 T cells and CD4 T/CD8 T cells. The results showed that the increase of PM2.5 was associated with the changes of inflammatory marker (hs-CRP) and immune markers (IgA, IgM, IgG, IgE and CD8 T cells) both in winter and summer. By contrast with the findings in the above markers, we also observed no significant association between personal PM2.5 and CD4 T/CD8 T cells both in winter and summer. Additionally, the increase of personal PM2.5 exposure induced a decrease of CD4 T cells (although not a statistically significant decrease) in participants. However, we observed a significant association between personal PM2.5 and CD8 T cells. Meanwhile, effect estimates were higher for hs-CRP, CD8 T cells, CD4/CD8 T cells, IgE and IgA in winter than those in summer, but not for IgG and IgM.

    View this table:
    Table 3

    Association of personal PM2.5 exposure with immunoglobulins, T cells and markers of inflammation (% change (95% CI))

    Discussion

    Our study observed the association linking individual-level PM2.5 exposure and cardiovascular disease-related inflammatory markers, immune parameters and lymphocyte profiles in traffic policemen. The results indicated that exposure to high levels of PM2.5 is significantly associated with systemic inflammatory markers and immune response both in winter and summer. The key finding of our study was that the increase of PM2.5 is associated with the increase of hs-CRP, IgM, IgG and IgE and decrease of IgA and CD8 T cells, which was in line with the hypothesis that exposure to high levels of PM2.5 is potentially associated with cardiovascular injury.

    Recently, most studies have investigated and found that acute effects of PM might trigger an acute cardiovascular event.35–38 However, the biological mechanisms of the effects of PM on cardiovascular disease are still unclear. Because of their small size, PM2.5 is inhaled deeply into the lungs, with a portion depositing in the alveoli and entering the pulmonary circulation and presumably the systemic circulation, which indicated that particles could enter into blood through lung and affected cardiovascular system.39 In Shanghai, PM2.5 air pollution is far in excess of the American air quality standards of 35 μg/m3 (24 h averaging time) and WHO air quality guideline 25 μg/m3 (24 h averaging time). Our findings showed that there were only a few traffic policemen whose individual-level PM2.5 was lower than 35 μg/m3, and that most traffic policemen were exposed to high concentrations of PM2.5 especially in winter. The results indicated that the traffic-related occupational population has a very high risk of exposure to high concentrations of PM2.5.

    One of the strengths of this study was using individual-level PM2.5 concentration to assess the traffic policemen's actual PM2.5 exposure when comparing with previous studies in which the PM concentrations were mathematically estimated either using a simple area average of the ambient concentrations40 or the spatial correlation based on ambient estimations at the participants’ primary homes,28 and these data may not be representative of the actual exposure that the study participants experienced. By contrast, Brauer et al41 studied 16 non-smoking chronic obstructive pulmonary disease patients equipped with a PM2.5 monitor for seven 24 h periods.

    In this study, after monitoring the 24 h individual-level PM2.5, the biological effects of PM2.5 on systemic inflammation and immune injury were measured in participants, which was based on the previous study that exposure to PM (EHC-93, 10 mg/kg) caused maximal pulmonary inflammation at 24 h postinstallation.42 Because environmental inhalation exposures, such as smoking or regular exposure to biomass smoke have been shown to induce a chronic low-grade inflammatory state,43 ,44 our participants had been limited to non-smokers. Multiple linear regression models were used to evaluate the association between individual-level PM2.5 and inflammatory marker, immune parameters and lymphocyte profiles by adjusting for BMI, categorised educational time period, regular alcohol intake and weekly working hours. The results indicated that traffic-related PM2.5 exposure was associated with the increase of hs-CRP in traffic policemen. The result was consistent with a previous study that long-term residential exposure to high levels of PM2.5 was associated with systemic inflammatory markers.26 Meanwhile, because of the difference of ambient PM2.5 concentration in winter and summer, the mean individual-level PM2.5 concentration in participants is higher in winter than summer. Along with our previous experimental study in which PM2.5 exacerbated cardiac injury and increased the systemic hs-CRP in rats in a dose-dependent manner,13 these findings supported the hypothesis that systemic inflammation was a pathway through which PM2.5 can lead to an acute increase in cardiac risk.

    This study determined the changes of cellular and humoral immune system in traffic policemen exposed to high concentrations of PM2.5. We found that the systemic CD4 T cells, CD8 T cells and CD4/CD8 T cells were lower in winter than in summer, whereas the levels of IgG and IgM were higher in winter than in summer. In the multiple linear regression models, an increase of individual-levels PM2.5 was significantly associated with the increase of IgG, IgM and IgE and decrease of IgA, CD8 T cells and CD4 T cells. although there has been no statistical decrease of CD4. Similarly, ambient concentrations of PM2.5 during the last 2 weeks of gestation were associated with decreases in the percentages of CD3, CD4 and CD8 T-lymphocytes in newborns.45 The difference from our results were that the association was stronger for the percentage of CD4 cells than for the percentage of CD8 subsets. Additionally, living in a highly polluted urban area was related to a lower percentage of CD4 T-lymphocytes and a lower CD4 to CD8 ratio46 in the cord blood among newborns from the Czech Republic. Along with these evidences, our study suggested that traffic policemen's exposure to PM2.5 was associated with the decrease of T-lymphocytes. One possible conclusion of our findings was that exposure to ambient PM2.5 is associated with the suppression of the cellular immune system. At the same time, the results indicated that traffic policemen exhibited significant increase of immunoglobulin (IgG, IgM and IgE), suggesting the activation of the humoral immune system. Other evidence showed that the offspring of residual oil fly ash (ROFA)-exposed mothers showed increased allergen-specific IgE and IgG levels.47 Overall, the findings supported the potential role of PM2.5 on the up-regulation of immunoglobulin. IgE can augment humoral and cellular immune responses to allergens. There are some evidences that particles or diesel exhaust particles could increase IgE levels.48 ,49 More importantly, because PM2.5 can enhance production of the T helper cell type 2 (Th2)-related cytokines IL-4 and IL-1350 which can lead to the production of IgE, our results indicated that ambient PM2.5 was potentially associated with allergic reaction. Moreover, the results demonstrated that the level of IgG increased with the increase of PM2.5. Other research conducted by the Central European Study of Air Quality and Respiratory Health found consistent association of PM2.5 and IgG in children.25 In our results, a distinctly different result was that PM2.5 induced a significant decrease of IgA in the adjusted linear model. Study in children consistently suggested a significant decrease of IgA concentration in salivary secretory of passive smokers.51

    In conclusion, we have shown a significant association between ambient PM2.5 exposure and systemic inflammatory markers and immune response in traffic policemen, and traffic policemen exhibited a high risk of developing cardiovascular diseases. Although the biologic relevance of this finding is not entirely clear, the observation of note is that the immune system may be altered by exposure to PM2.5. Further research is needed to explore the correlative immuoregulatory mechanisms linking PM2.5 and immune cells. The study strengthened our confidence in the applicability of the chosen hs-CRP, T cells and immunoglobulin for the investigation of short-term PM exposure. Considering the role of these markers as potential mediators in the pathogenesis of atherosclerotic disease, these results provide a link between short-term and long-term PM2.5 exposure, and the hypothesised development and progression of cardiovascular disease.

    Acknowledgments

    The authors thank the participants and all who were involved in the surveys.

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    Footnotes

    • Contributors GHW, LYZ and PKL: data collection and supervision; YJ and XLQ: data entry and management for statistical analysis; X Zhang: drafting of the manuscript; ZHZ: critical revision of the manuscript.

    • Funding This work was supported by grants from the National Natural Science Foundation of China (No. 81001229, 81172617), Natural Science Foundation of Shanghai, China (No. 09ZR1402400) and the National High Technology Research and Development Program of China (No. 2007AA06Z409).

    • Competing interests None.

    • Patient consent Obtained.

    • Ethics approval Human Studies Review Committee of the Foundation of school of public health, Fudan University.

    • Provenance and peer review Not commissioned; externally peer reviewed.