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Departments of
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Internal Medicine,
Medical Research, and
Clinical Pathology, Chang Gung Memorial Hospital, Kaohsiung, Taiwan
| Abstract |
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, IL-6, and IL-10, and nitrite/nitrate levels were not significantly elevated. In contrast, TGF-
and PGE2 levels were significantly elevated in SARS patients. Five of the 15 SARS patients had detectable coronaviruses in blood, but patients with detectable and undetectable viremia had no different profiles of immune mediators. Flow cytometric analysis of MAPKs activation by phospho-p38 and phospho-p44/42 (extracellular signal-regulated kinase) expression showed that augmented p38 activation (p = 0.044) of CD14 monocytes associated with suppressed p38 activation (p = 0.033) of CD8 lymphocytes was found in SARS patients. These results suggest that regulation of TGF-
and PGE2 production and MAPKs activation in different leukocytes may be considered while developing therapeutics for the SARS treatment. | Introduction |
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A histology of lung necropsy from SARS patients showed that abundant foamy macrophages and multinucleated syncytial cells were demonstrated (3, 6). Thus, cytokine storm has been proposed to be involved in the rapid course of ARDS in SARS patients (2, 3, 6). In contrast, the facts that there is a higher mortality in SARS patients older than 65, and that certain SARS patients tended to have coinfection (1, 2, 3) suggest that immunosuppression might also play a role in the pathogenesis. In an attempt to determine whether proinflammatory cytokines or skewed Th (Th1/Th2) cytokines were involved in the pathogenesis of SARS, we collected plasma from SARS patients and controls for measuring proinflammatory cytokines TNF-
, IL-6, and IL-8, as well as Th reaction mediators IL-2, IL-12, IL-10, TGF-
, NO, or PGE2 production. Previous studies with certain viruses including murine coronavirus have shown that inhibition or activation of mitogen-activated protein kinase (MAPK) was involved in induction or suppression of cytokines after virus infection (7, 8). We therefore harvested blood leukocytes in 1% formaldehyde for flow cytometric analysis of intracellular MAPK activation, as demonstrated by phospho-p38 and phospho-extracellular signal-regulated kinase (ERK) expression after plasma collection. The blood cytokines and immunomediators in SARS patients were also related to the intracellular expression of MAPK activation in this study.
| Materials and Methods |
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On April 26, 2003, an index case who initially presented with flank pain and fever from Taipei was admitted to our hospital at Kaohsiung, southern Taiwan. This patient was not suspected of SARS until April 30. From May 2 to 17, 2003, a cluster of SARS patients including inpatient cases, family caregivers, and health care workers developed probable SARS. We recruited those who were previously healthy adults for this study in a paired case-control design. Once we had recruited 13 SARS patients, we included 13 age-matched normal adults for blood collection of immune studies. Confirmation of SARS infections was determined by positive RT-PCR detection of coronavirus in acute stage or detectable coronavirus-specific Ab by ELISA in convalescent stage.
Preparation of plasma and leukocytes under a safety procedure
Studies proceeded with a safety procedure. The safety procedure for this study was approved by the Institute Review Board of this hospital. Because the clinical progression of SARS was usually uniform and categorized into two stages, 1) febrile pneumonitis in the first week and 2) shifting pneumonitis, even progressing to ARDS, between the second and third weeks (2, 3, 4) and therefore collected whole blood (4 ml) within 7 days and between the second and third weeks of admission. The blood samples were separated into plasma and blood cells by centrifugation at 1500 x g for 15 min. The plasma was harvested for cytokine determination after heat inactivation at 56°C for 15 min, and the blood cells were separated into RBC and white blood cells by dextran (T500, 4.5%) sedimentation (9). The white blood cells were subjected to inactivation of all known potential infectious agents and fixation of leukocytes by 1% formaldehyde. All of the procedures involving the plasma and leukocyte preparation were conducted in a P2 laboratory.
Measurement of blood cytokines and PGE2
Plasma PGE2 and cytokines TNF-
, IL-2, IL-6, IL-8, IL-10, IL-12, and TGF-
concentrations were measured by ELISA kits purchased from R&D Systems (Minneapolis, MN). Plasma aliquots at 0.1 ml were used for each individual ELISA, as described earlier (10). To compare the cytokine production in SARS patients with other infectious diseases, we included 15 plasma samples of our patients with dengue hemorrhagic fever, which were collected in the last year of dengue-2 outbreak in southern Taiwan. We also included 21 plasma samples from bacterial pneumonia with and without ARDS. Seven of the 21 pneumonia patients had ARDS, as defined by bilateral alveolar consolidation greater than two quadrants, oxygen index (PaO2/FiO2)
150, and peak end expiratory pressure
10 cm H2O (11).
Real-time RT-PCR detection of coronaviruses in blood
We subjected viral RNA extracted from plasma of the controls and patients with SARS to a fluorogenic quantitative RT-PCR detection of total virions in blood, as previously described (12). In brief, 140 µl of plasma was individually added with 560 µl of QIAmp viral RNA extraction solution (Qiagen, Valencia, CA) to cause inactivation and lysis of all potential infectious agents. The viral RNA was further purified by the QIAmp spin column and suspended to 40 µl, per the manufacturers recommendation. Each 10 µl RNA sample was subjected to a fluorescent quantitative RT-PCR by the TaqMan technology using ABI 7700 quantitative PCR machine (Applied Biosystems, Foster City, CA) for 45 cycles (12). The forward primer, the reverse primer, and the nested fluorescent probe sequence for detecting coronavirus were, respectively: 5'-CCT CTC TTG TTC TTG CTC GCA-3', 5'-TAT AGT GAG CCG CCA CAC ATG-3', and 5'-FAMTCG TGC GTG GAT TGG CTT TGA TGT-3' 6-carboxy-N,N,N',N'-tetramethylrhodamin (purchased from Applied Biosystems).
Measurement of blood nitrite/nitrate (NOx) levels
We measured plasma NOx levels to reflect NO production, as previously described (13). For measurement, NOx in the samples was converted into NO by a strong reducing agent, 0.4% VCl3 (Boehring Mannheim, Germany), in the presence of 2 N HCl. The NO analyzer (NO-Analyzer 280; Seivers, Denver, CO) allows the interaction of NO with ozone to elicit chemiluminescence (NO + O3
NO2· + O2; NO2·
NO2 + hv). A small amount of plasma (50 µl) was subjected to measurement by the NO analyzer after alcohol precipitation of protein in the samples at 1:2 (v/v) ratio. The NOx levels in each sample were determined by an interpolation of a standard curve made from a series of well-known concentrations of sodium nitrate (13).
Flow cytometric analysis of intracellular activated MAPKs in different leukocytes
Activated MAPKs in leukocytes were demonstrated by flow cytometric analysis of intracellular phospho-p38 and phospho-p44/42 (ERK) expression, as previously described (14). This method has been shown to be more rapid and sensitive than classical methods in human T cells (15). For experiments, 1% formaldehyde-fixed leukocytes were subjected to cell permeabilization by methanol at 1/4 (v/v) for 30 min after washing twice in PBS. The permeated leukocytes in 0.1-ml aliquots (1 x 106 cells/ml) were subjected to dual staining of cell surface molecules by PE-conjugated mouse anti-human CD4, CD8, or CD14 Abs (BD PharMingen, Franklin Lakes, CA), and intracellular signal molecules by rabbit anti-human phospho-p38 or phospho-p44/42 (ERK) Abs (Cell Signaling Technology, Beverly, MA) for 30 min. This was followed by recognition with FITC-conjugated goat anti-rabbit Ig Abs for another 30-min staining. After washing twice with PBS, the reactions were suspended in 0.3 ml of PBS for flow cytometric analysis.
Statistics
Data of cytokine measurement are presented with mean ± SE and statistically analyzed by Students t test. Expression of MAPK activation was presented with mean intensities of intracellular phospho-p38 and phospho-ERK levels. The mean fluorescent intensities of intracellular phospho-p38 and phospho-ERK levels between patient and control groups were analyzed by Students t test.
| Results |
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Fifteen SARS patients aged 2345 and 15 normal controls aged 2941 were studied. The 15 SARS patients, who were previously healthy, all had typical SARS symptoms/signs, showing fever (>38°C) and varying extent of pneumonia on chest radiography. Patients initially often presented leukopenia (mean 4,360 cells/cumm), thrombocytopenia (mean 145,470/µl), and profound lymphopenia (mean 610 cells/cumm). Monocytes were not significantly different between SARS patients and controls (Table I). Normal or elevated lactate dehydrogenase and creatine phosphokinase were noted. These patients were treated under a protocol with initial institution of ribavirin 400 mg/m2/day in the first 7 days after a loading dose of 2 g. These patients were allowed to receive steroid (methylprednisolone, 1 mg/kg/day) after 7 days of admission while there was an exacerbation of pneumonitis. The initial blood samples for immune studies from all these patients were collected between 3 and 7 days of admission, whereas 9 of the 15 patients started receiving methylprednisolone (1 mg/kg/day) with and without pulse therapy (500 mg every 12 h for 2 days) while exacerbated pneumonitis or ARDS occurred.
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It was found that plasma IL-8 levels were significantly higher in SARS patients than in normal controls in the first week of illness (mean ± SD: 108.5 ± 30.0 vs 73.3 ± 4.4 pg/ml; p = 0.016). The elevated IL-8 levels returned to normal between second and third weeks (Fig. 1A). As shown in Fig. 1C, plasma IL-2 levels in patients with SARS were not significantly higher in the early stage (16.4 ± 3.5 vs 23.1 ± 5.6). However, the IL-2 levels were significantly higher in the second to third week of the illness (16.4 ± 3.5 vs 32.3 ± 5.3; p = 0.039). The elevated IL-8 levels in SARS patients were lower than those in the patients of bacterial pneumonia with ARDS, and those in the patients with dengue hemorrhagic fever (Fig. 2A). Similarly, plasma TNF-
levels in SARS patients were also lower than those with non-SARS ARDS and those with dengue hemorrhagic fever (DHF) (Fig. 2B). In contrast, plasma TGF-
levels in SARS patients were significantly higher than those with non-SARS ARDS (Fig. 2C). The plasma PGE2 level in SARS patients was also higher than that in non-SARS ARDS patients, although it did not reach a significant difference (Fig. 2D). The plasma TNF-
(p = 0.305), IL-6 (p = 0.117), IL-10 (p = 0.609), IL-12 (p = 0.403), and NOx (p = 0.459) levels were not significantly different between patients and controls in the first week (Fig. 1 and Table II). TGF-
(p = 0.041) and PGE2 (p = 0.046) levels were significantly elevated in early stage of patients with SARS than those in age-matched normal controls (Table II). The PGE2 levels were still significantly elevated, but the IL-12 levels in SARS patients were significantly depressed, in the late stage (second to third week), while plasma TNF-
and IL-10 levels remained at no significant change (Table II). The SARS patients with (n = 9) and without (n = 6) methylprednisolone treatment had no significant differences in IL-8 (p = 0.581), TGF-
(p = 0.802), and PGE2 (p = 0.921) levels in the late stage of the illness. One patient died of a rapid course of spontaneous pneumothorax and another patient developed pulmonary fibrosis; both had increased TGF-
and PGE2 levels, but not IL-2, IL-10, IL-12, IL-8, or TNF-
levels. The other 13 patients in this study completely recovered without apparent sequelae.
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Two plasma samples from each patient with SARS and one plasma sample from normal controls were subjected to a real-time RT-PCR detection of coronavirus in blood. Five of the 15 SARS patients had detectable coronavirus RNA in blood, while none of the 15 controls had detectable coronavirus RNA (Fig. 3A). The coronavirus titers in blood were lower, at a range between 42 and 193 virions/ml, similar to the titer at 190 virions/ml reported by others (16). Patients with and without detectable viremia did not differ in plasma IL-8, TGF-
, or PGE2 levels (Fig. 3, BD). The patient who died of spontaneous pneumothorax had no detectable coronavirus in blood on days 3 and 9. Another patient with pulmonary fibrosis also had no detectable virus on days 3 and 11. This suggests that the viremia in SARS infections may not be correlated to clinical severity.
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Using formaldehyde-fixed peripheral blood leukocytes, we first measured the phosphorylated p38 MAPK levels in total leukocytes from patients with SARS and age-matched normal controls in early stage. As shown in a pilot study (Fig. 4A), it was found that SARS patients had an increase in intracellular phospho-p38 level. Results calculated from 15 paired experiments showed that the intracellular phospho-p38 levels in total leukocytes were significantly higher in patients than in controls (Fig. 4B). Further studies showed that CD14-positive monocytes were the leukocytes in SARS patients showing an increase in phospho-p38, but not phospho-p44/42 ERK expression (Fig. 5A). CD4-positive T cells from SARS patients appeared to have a suppressed intracellular phospho-ERK level, but it did not reach a significant difference (Fig. 5B). CD8-positive T cells from SARS patients did, however, have a significantly lower intracellular phospho-p38 level in early stage (Fig. 5C). The phospho-p38 expression in CD8 cells remained significantly suppressed in 23 wk after admission, while those in CD14 and CD4 cells no longer had significant increase or decrease of phospho-p38 expression.
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| Discussion |
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, IL-6, and IL-8 levels. The blood cytokines in SARS patients are much lower than those in other infections with systemic illness such as bacterial pneumonia with ARDS or patients with dengue hemorrhagic fever. The IL-8 levels observed in our SARS patients were
6-fold lower than those reported in septic patients described by Headley et al. (21). This suggests that proinflammatory cytokine storm is unlikely involved in the pathogenesis of SARS infections. In contrast, an early elevation of immunosuppressive mediators PGE2 and TGF-
associated with later elevation of IL-2 levels may partly explain why SARS patients tended to have a longer clinical course and coinfections (2, 22). This inference is, however, hampered by the limitation of blood cytokine level measurements in determining local or organ-specific immune response pattern. Patients with SARS usually have a prolonged virus shedding in throat, sputum, and feces (2, 16). The virus load in sputum is much higher than those in other specimens. In a real-time RT-PCR analysis of virus load in three patients, Drosten et al. (16) showed that only 1 of the 3 patients had detectable viruses in blood with 106 times lower than those in sputum. Correlation of coronaviruses in blood to clinical outcomes has not been clarified. In Ebola infections, a detectable viremia with impaired humoral reaction is correlated to fatal outcomes (17, 18). In the present study, we found that 5 of the 15 patients had detectable blood coronavirus RNA. Patients with and without detectable viremia had no different profiles of blood immune mediators, suggesting that viremia in SARS infections may not be the trigger to raise altered immune reaction in blood. Viral replication or altered immune reaction in target tissue may be responsible for the elevation of immunosuppressive mediators in the circulation of SARS patients.
Patients with SARS usually have a rapid progression of pneumonitis (2, 3, 4). Approximately one-third of the SARS patients developed ARDS, one-tenth of the patients succumbed to death, and one-tenth of patients revealed pulmonary fibrosis (2, 3, 4). Histological examinations of lung necropsy from SARS patients have demonstrated infiltration of inflammatory cells associated with foamy macrophages, multinuclear syncytial cells, and occasional hemophagocytic features (3, 6). This has raised the possibility of immunopathological damage of lung tissues. Results from this study showed that an augmented p38, but not p44/42 ERK, MAPK activation in CD14 cells was associated with elevated IL-8 levels in SARS patients. It is limited to directly infer the p38 activation of CD14 monocytes responsible for elevated blood IL-8 levels without simultaneously measuring intracellular IL-8 and phospho-p38 levels in CD14 monocytes. Results from this study, however, suggest that altered leukocyte p38 activation may contribute to abnormal blood cytokine profile in SARS patients. This is similar to a study with murine coronaviruses, showing that murine coronaviruses could activate p38 and c-jun kinases, but not p44/42 ERK, that are responsible for IL-6 induction (7). Yao et al. (8) reported that hepatitis C core protein could inhibit ERK activation in T cells, resulting in lower IL-2 induction. In our study, we did not find a significant inhibition of ERK activation in SARS infections, but found a slower increase of IL-2 levels in SARS infections. The slower increase of IL-2 production may not be related to ERK activation, but possibly related to altered p38 activation in different leukocytes from SARS patients. Thus, further studies are needed to explore whether increase of p38 activation in monocytes, but decrease of p38 activation in CD8 lymphocytes from SARS patients is really related to increase of immunosuppressive mediators or virus replication in the lung tissues.
Currently, many efforts are now ongoing to develop a vaccine and anti-SARS medication. Another, faster strategy for the SARS treatment is to expose the immune response to the SARS infection and target the altered immunity. The treatment of SARS patients with steroid remains controversial. The fact that SARS patients had elevated immunosuppressive TGF-
and PGE2 mediators, but not proinflammatory cytokines TNF-
, IL-6, IL-8, and IL-10 in the early stage (first week), associated with later elevated IL-2 levels in SARS patients, suggests that administration of steroid in the early stage may not be suitable, but can be considered in the late stage (second to third week). Based on our study showing discordant p38 MAPK activation in different leukocyte populations and elevated circulating TGF-
and PGE2 levels, it is postulated that regulation of TGF-
and PGE2 production and p38 MAPK activation may be considered while developing therapeutics for the SARS treatment.
| Acknowledgments |
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| Footnotes |
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2 C.-H.L. and R.-F.C. contributed equally to this work. ![]()
3 Address correspondence and reprint requests to Dr. Kuender D. Yang, Department of Medical Research (12F12L), Children Hospital Building, Chang Gung Memorial Hospital at Kaohsiung, 123 Ta-Pei Road, Niau-Sung, Kaohsiung 833, Taiwan. E-mail address: yangkd{at}adm.cgmh.org.tw ![]()
4 Abbreviations used in this paper: SARS, severe acute respiratory syndrome; ARDS, adult respiratory distress syndrome; DHF, dengue hemorrhagic fever; ERK, extracellular signal-regulated kinase; MAPK, mitogen-activated protein kinase; NOx, nitrite/nitrate. ![]()
Received for publication September 16, 2003. Accepted for publication March 29, 2004.
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in sera of children with dengue. J. Clin. Invest. 88:1473.
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