REVIEW article

Front. Pharmacol., 14 February 2022

Sec. Inflammation Pharmacology

Volume 13 - 2022 | https://doi.org/10.3389/fphar.2022.802228

Increased Circulating Cytokines Have a Role in COVID-19 Severity and Death With a More Pronounced Effect in Males: A Systematic Review and Meta-Analysis

  • 1. State Key Laboratory of Quality Research in Chinese Medicine, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Macao, China

  • 2. Dr. Neher’s Biophysics Laboratory for Innovative Drug Discovery, Macau University of Science and Technology, Macao, China

  • 3. Department of Urology, The Fifth Affiliated Hospital of Sun Yat-Sen University, Zhuhai, China

  • 4. Institute of Traditional Chinese Medicine Research, Tianjin University of Traditional Chinese Medicine, Zhuhai, China

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Abstract

Background: Coronavirus disease 2019 (COVID-2019), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a worldwide epidemic and claimed millions of lives. Accumulating evidence suggests that cytokines storms are closely associated to COVID-19 severity and death. Here, we aimed to explore the key factors related to COVID-19 severity and death, especially in terms of the male patients and those in western countries.

Methods: To clarify whether inflammatory cytokines have role in COVID-19 severity and death, we systematically searched PubMed, Embase, Cochrane library and Web of Science to identify related studies with the keywords “COVID-19″ and “cytokines”. The data were measured as the mean with 95% confidence interval (CI) by Review Manager 5.3 software. The risk of bias was assessed for each study using appropriate checklists.

Results: We preliminarily screened 13,468 studies from the databases. A total of 77 articles with 13,468 patients were ultimately included in our study. The serum levels of cytokines such as interleukin-6 (IL-6), IL-10, interleukin-2 receptor (IL-2R), tumor necrosis factor (TNF)-α, IL-1β, IL-4, IL-8 and IL-17 were higher in the severity or death group. Notably, we also found that the circulating levels of IL-6, IL-10, IL-2R and TNF-α were significantly different between males and females. The serum levels of IL-6, IL-10, IL-2R and TNF-α were much higher in males than in females, which implies that the increased mortality and severity in males was partly due to the higher level of these cytokines. Moreover, we found that in the severe and non-survivor groups, European patients had elevated levels of IL-6 compared with Asian patients.

Conclusion: These large-scale data demonstrated that the circulating levels of IL-6, IL-10, IL-2R, IL-1β, IL-4, IL-8 and IL-17 are potential risk factors for severity and high mortality in COVID-19. Simultaneously, the upregulation of these cytokines may be driving factors for the sex and region predisposition.

Introduction

Coronavirus disease 2019 (COVID-2019), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has raised major public health crises since 2019. Though many patients with COVID-19 present no symptoms or only mild symptoms (including fever, cough, and fatigue), some suffer severe symptoms and may progress to pneumonia, acute respiratory distress syndrome (ARDS), multi organ dysfunction and even death. The severity of COVID-19 is known to be closely correlated to cytokines storms, when the immune system is unable to counteract the virus, cytokine storms in patients may lead to macrophage hyperactivity and further systemic abnormal reactions (Lang et al., 2020; Liang et al., 2020; Makaronidis et al., 2020). However, the characteristics of the cytokine storms in COVID-19 patients have not been fully illustrated.

In death cases, patients with COVID-19 shows a higher risk of mortality in males sex (Griffith et al., 2020). According to the largest sex-disaggregated data from 47 countries, men with COVID-19 have higher morbidity than women with COVID-19 (63.8% men; 36.2% women). In addition, the overall mortality of COVID-19 is more than 2.3 times higher in men than in women (Control and Response, 2020). The discrepancy in COVID-19 outcomes between male and female patients may be attributed to several biological and social factors, especially cytokine storms (Griffith et al., 2020). Moreover, as the Covid-19-related literatures grows increasingly, the racial and ethnic disparities showed that the death and severity rate of Asians are lower than the other population (Tirupathi et al., 2020a; Mackey et al., 2021a).

To this end, we conducted a systematic review and meta-analysis to identify the key factors associated to COVID-19 severity and death, especially in terms of the sex and race bias detected in severe COVID-19 patients.

Methods

Search Strategy

We screened databases (Web of Science, Embase, the Cochrane Library, and PubMed) from December 2019 to June 2021. We also registered on the INPLASY (International Platform of Registered Systematic Review and Meta analysis Protocols platform). The number for our study is INPLASY2021120050. To search for more articles, we also screened related reference lists from relevant studies. The search terms included (“2019 novel coronavirus disease”) OR (“COVID19”) OR (“COVID-19 pandemic”) OR (“SARS-CoV-2 infection”) OR (“COVID-19 virus disease”) OR (“2019 novel coronavirus infection”) OR (“2019-nCoV infection”) OR (“coronavirus disease 2019”) OR (“coronavirus disease-19”) OR (”2019-nCoV disease”) OR (“COVID-19 virus infection”) OR (“cytokines”).

Inclusion and Exclusion Criteria

All the included studies met the following criteria: 1) the types of studies considered for inclusion were prospective or retrospective cohort studies comparing mild groups and severe groups; 2) the circulating levels of cytokines were analyzed before treatment. The exclusion criteria were reviews, studies of interventions other than cytokines, in vitro studies and in vivo animal experiments. To further reduce the accidental error of our study, each analysis of cytokines should contain more than two studies. Only English studies were screened in our study. After screening and collecting the literature, two authors removed duplicate publications by Endnote and independently evaluated each study based on their title and abstract. The symptom criteria are listed as follows.

For the mild group, patients had respiratory symptoms (fever, cough, fatigue, anorexia, headache), without evidence of viral pneumonia or hypoxia.

For the severe group, patients had one or more of the following conditions: respiratory distress, respiratory rate ≥30 times/minute, oxygen saturation (SpO2) ≤93% at rest, arterial partial pressure of oxygen (PaO2)/Fraction of inspiration O2 (FiO2) in arterial blood ≤300 mmHg, >50% lung imaging progress in the short term within 24–48 h, respiratory failure and mechanical ventilation required, shock, combined with other organ failure, and transfer to the intensive care unit (8).

Data Extraction and Quality Assessment

Two authors (Hu & Pan) collected data from the included studies, including the first author, study country, inclusion time, age, sex, sample sizes, mild group/severe group, survivors/non-survivors, study design, and outcomes. Another two authors assessed the quality of the studies using the Newcastle-Ottawa Scale (NOS) and scored points for each included study independently.

Statistical Analysis

Review Manager 5.3 was used to perform all statistical analyses. The mean and standard deviation (SD) were used as measurements across articles. We calculated the sample mean and SD by the sample size and interquartile range (IQR) (Wan et al., 2014; Luo et al., 2018). The circulating levels of cytokines between different groups were collected from the selected articles and analyzed using a random-effects model when I2>50%. The standard Cochran’s Q test and I2 statistics were also used to identify heterogeneity from the included articles. Significant heterogeneity was determined when I2 value > 50% and p-value <0.05.

Results

Large Scale Data From Clinical Reports

A total of 13,468 studies were screened out by the database search. After removing 826 duplicates, we excluded 8452 articles by reading the titles and abstracts of the studies. Then, we read the remaining literature and excluded studies that were not matched to the inclusion and exclusion criteria. There were 77 articles with 13,986 patients ultimately included in this study (Han et al., 2020; Yang et al., 2020; Rutkowska et al., 2021) (Figure 1). The baseline features of all included studies are presented in Table 1.

FIGURE 1

FIGURE 1

Literature search and screening process.

TABLE 1

AuthorStudy regionInclusion timeMean age (years)genderSample sizesMild group/Severe groups or survival/non-survival groupsStudy designOutcomesJournal types
Ai-Ping Yang Yang et al. (2020)ChinaN/A46.460% male9369/24retrospective cohortIL-6, IL-10, TNF-α, IL-1β, IL-4, IL-8, IL-17Normal
Bo Xu Xu et al. (2020a)China26 Dec 2019 to 1 Mar20206255% male187159/28retrospective observational studyIL-6, IL-10, TNF-α, IL-1βNormal
Changcheng Zheng Zheng et al. (2020a)China15 Feb 20206043.6 male5534/21retrospective observational studyIL-6Normal
Changsong wang Wang et al. (2020a)ChinaN/A62.950% male4533/12retrospective cohortIL-6, IL-10, IL-4Normal
Chaomin Wu Wu et al. (2020a)China25 Dec 2019, to 26 Jan 20205143.7% male201117/84retrospective cohortIL-6Normal
Chuan Qin Qin et al. (2020a)ChinaJan 10 to 12 Feb 20205852% male452166/286retrospective observational studyIL-6, IL-2R, IL-10, TNF-α, IL-8Normal
Egon Burian Burian et al. (2020)GermanMar and April 202061.5435% male6537/28retrospective cohortIL-6Normal
Fangfang Liu Liu et al. (2020a)ChinaJan 20 to 23 Feb 20204855.38% male6542/23retrospective cohortIL-6Normal
Fei Zhou Zhou et al. (2020a)China29 Dec 2019 to 31 Jan 20205662% male191137/54retrospective cohortIL-6Normal
Fengqin Zhang Zhang et al. (2020a)ChinaFeb to March 2020N/AN/A3427/7retrospective observational studyIL-6, IL-10, TNF-α, IL-8Normal
Guang Chen Chen et al. (2020a)ChinaJan 2–7, 20205681% male2110/11retrospective observational studyIL-6, IL-2R, IL-10, TNF-α, IL-8Normal
Haijun Wang (Wang et al., et al.)ChinaJan 2 to 5 Feb 20204943.6% male8333/50retrospective cohortIL-6Normal
Han Huang Han et al. (2020)ChinaJan 2020 and February 2020N/A50% male10242/60retrospective cohortIL-6, IL-10, TNF-α, IL-4Normal
Hong Huang Huang et al. (2020)ChinaFeb and March 20203646% male3127/4retrospective cohortIL-6, IL-10, TNF-α, IL-2RNormal
Hua Fan Fan et al. (2020)China30 Dec 2019 to 16 Feb 202058.3667% male7347/26retrospective observational studyIL-6Normal
Huizheng Zhang Zhang et al. (2020b)ChinaN/AN/A51.2% male4329/14retrospective observational studyIL-6, IL-10, TNF-α, IL-17Preprint
Jia Ma Ma et al. (2020)China1 Jan 2020 to 30 Mar 20206254.5% male3717/20retrospective observational studyIL-6Normal
Lang Wang Wang et al. (2020b)ChinaJan 1 to 6 Feb 20207149% male339274/65retrospective observational studyIL-6Normal
Lei Liu Liu et al. (2020b)ChinaN/A4562.7% male5144/7retrospective case seriesIL-6Preprint
Lucas Quartuccio Quartuccio et al. (2020)ItalyN/A66.579% male2418/6retrospective cohortIL-6Normal
Maria effenberger Effenberger et al. (2020)Austria26th February to 21st April 202060.6962.5% male9681/15retrospective case seriesIL-6Normal
María J. Pérez-Sáez Pérez-Sáez et al. (2020)Spain18th March 202059.367.5% male8054/26retrospective case seriesIL-6Normal
Mario Fernández‐Ruiz Fernández-Ruiz et al. (2020)Spain16th March to 27th March 202046.865.9% male8839/49retrospective cohortIL-6Normal
Marta Crespo Crespo et al. (2020)SpainMar to April 20207175% male168/8Prospective cohort studyIL-6Normal
Miao Luo Luo et al. (2020)ChinaJan and March 20206151.2% male1018817/201retrospective cohortIL-2R, IL-6, IL-10, TNF-α, IL-8Normal
Michael Dreher Dreher et al. (2020)GermanFeb and March 20206566% male5026/24retrospective case seriesIL-6Normal
Ming Ni Ni et al. (2020)China1 to 21 February 20206050% male27male 14/female 13retrospective case seriesIL-6, IL-10, TNF-αNormal
Paola Toniati Toniati et al. (2020)ItalyMar 9th and 20 Mar 20206288% male10077/23retrospective case seriesIL-6Normal
Pingzheng Mo Mo et al. (2020)ChinaJan 1st to 5 Feb 20205455.5 male15570/85retrospective observational studyIL-6Normal
Qin Lu Qin et al. (2020b)China26 January 2020 and 5 February 202055.257.9 male233135/98retrospective cohortIL-6, IL-2R, IL-10, TNF-αNormal
Qiurong Ruan Ruan et al. (2020)ChinaN/AN/AN/A15082/68retrospective observational studyIL-6Normal
Ruirui Wang Wang et al. (2020c)ChinaJan 20 to 9 Feb 202038.757% male125100/25retrospective descriptive studyIL-6Normal
Shaohua Li Li et al. (2020a)China20 Jan 2020, to 20 Mar 202048.558% male6943/26retrospective cohortIL-6, TNF-α, IL-1β, IL-8Normal
Susu He He et al. (2020)ChinaJan 17 to 12 Feb 202044.553% male9360/33retrospective cohortIL-6. IL-10Normal
Suxin Wan Wan et al. (2020)China26 January to 4 February 202043.153.6% male123102/21retrospective observational studyIL-6, IL-10, TNF-α, IL-4, IL-17Normal
Takahisa Mikami Mikami et al. (2020)United StatesMar and April 20205954.5% male28202014/806retrospective cohortIL-6, TNF-α, IL-8Normal
Tao Chen Chen et al. (2020b)China13 January to 12 February 20206262% male274161/113retrospective descriptive studyIL-6 IL-2R, IL-10 TNF-α, IL-8Normal
TAO Liu Liu et al. (2020c)ChinaDecember 2019 to July 202053.942.2% male7711/66retrospective cohortIL-6, IL-10Normal
Tielong Chen Chen et al. (2020c)China1 Jan 2020, to 10 Feb 20205453.2% male5536/19retrospective case seriesIL-6Normal
Tobias Herold Herold et al. (2020)GermanFeb 29 to 27 Mar 20206170% male8957/32retrospective case seriesIL-6Normal
Wenjun Tu Tu et al. (2020)China3 Jan to 24 February 20207076% male174149/25retrospective case seriesIL-6Normal
Xiaohong Yuan Yuan et al. (2020)ChinaFeb 15 to 30 Mar 20206747.9% male11761/56retrospective cohortIL6, IL-10, IL-4Normal
Xia Xu Xu et al. (2020b)China3 Feb 2020, to 20 Mar 20205740.91% male8847/41retrospective descriptive studyIL-6 IL-2R, TNF-α, IL-8Normal
Xiong Bei (Xiong et al., 2020)China21 Mar 20206661.4% male5719/38retrospective case seriesIL-6Normal
Yang Liu Liu et al. (2020d)China22 Jan 2020, to 15 Feb 20204564.4% male7646/30retrospective case seriesIL-6, IL-2R, IL-10, IL-1β, IL-8Normal
Yang Xu Xu et al. (2020c)ChinaN/A5750.7% male6944/25retrospective cohortIL-6Preprint
Yang Xu 2 Xu (2020)ChinaN/AN/AN/A108/2retrospective observational studyIL-6Preprint
Yang Zhao Zhao et al. (2020)ChinaJan 13 and 4 Mar 20205847.3% male539414/125retrospective observational studyIL-6Normal
Yangjing Xie Xie et al. (2020)ChinaFeb and March 20206643.5% male6238/24retrospective cohortIL-6Normal
Yanli Wang Wang et al. (2020d)China25 Jan 2020 and 8 Mar 20205265% male4335/8retrospective observational studyIL-6, IL-10, IL-4Normal
Yaqing Zhou Zhou et al. (2020b)China28 Jan 2020 to 2 Mar 20206665.9% male218/13retrospective case seriesIL-6Normal
Yi Li Li et al. (2020b)China28 January 2020, to 12 March 2020656.8% male12548/77retrospective case seriesIL-6, IL-10, TNF-α, IL-4Normal
Ying Chi Chi et al. (2020)ChinaN/A45.2156% male6658/8retrospective case seriesIL-6, IL-2R, IL-10, TNF-α, IL-1β, IL-4, IL-8, IL-17Normal
Yingjie Wu Wu et al. (2020b)China29 December 2019 to 20 February 20206163.3% male7132/39retrospective case seriesIL-6, IL-10, TNF-α, IL-4Normal
Ying Sun Sun et al. (2020)ChinaN/A4758.7% male6319/44retrospective case seriesIL-6Normal
Yi Zheng Zheng et al. (2020b)ChinaJan. 22 and Mar. 5, 20206667.6% male3419/15retrospective cohortIL-6, IL-10Normal
Yong Gao Gao et al. (2020)China23 Jan 2020 to 2 Feb 20204460.6% male4328/15retrospective case seriesIL-6Normal
Zhe Zhu Zhu et al. (2020)ChinaJan 23 to Feb20, 202050.936.43% male127111/16retrospective cohortIL-6, IL-10, TNF-α, IL-4Normal
Zhihua Lv Lv et al. (2020)China4 Feb 2020 to Feb28, 20206249.4% male354115/239retrospective cohortIL-6, IL-10, TNF-α, IL-4Normal
Zhilin Zeng Zeng et al. (2020)China28 Jan 2020, to 12 Feb 20206251.1% male31793/224retrospective cohortIL-6, IL-2R, IL-10, TNF-αNormal
Zhongliang Wang Wang et al. (2020e)ChinaDec 2019 to February 20204246% male6955/14retrospective cohortIL-6, IL-10, TNF-α, IL-4Normal
Sophie Hue Hue et al. (2020)FranceMar 20206091% male3825/13retrospective cohortIL-6, IL-10Normal
Elzbieta Kalicinska Kalicińska et al. (2021)PolandDec 20206252% male8251/31, 54/28Prospective cohortIL-6, TNF-αNormal
Dianming Li Li et al. (2020c)ChinaMar 20205662.5% male6541/24retrospective cohortIL-6Normal
Francisco Javier Gil-Etayo Gil-Etayo et al. (2021)SpainSep 20205567% male3428/6Prospective cohortIL-6, IL-10Normal
Feng Gao Gao et al. (2021)ChinaFeb 20204942.5% male121102/19retrospective cohortIL-6, IL-10Normal
Wei Zhu Zhu et al. (2021)ChinaMar 20206545% male1106675/431retrospective cohortIL-6, IL2R, TNF-α, IL-8Normal
Zirui Meng (Meng et al. (2021)ChinaApr 20204853% male9871/27retrospective cohortIL-6, IL-10, TNF-α, IL-8Normal
Chenze Li Li et al. (2020d)ChinaApr 20206349.6% male989770/219, 141/78retrospective cohortIL-6, IL-2R, IL-10, TNF-α, IL-8Normal
Brahim Belaid Belaid et al. (2021)AlgeriaApr 20205970.18% male5731/26retrospective cohortIL-6, TNF-αNormal
Rocio Laguna-Goya Laguna-Goya et al. (2020)SpainApr 20205263.3% male501465/36Prospective cohortIL-6Normal
Jose J. Guirao Guirao et al. (2020)SpainApr 20206552% male5042/8, 36/14retrospective cohortIL-6Normal
Jose Marıa Galvan-Roman Galván-Román et al. (2021)SpainMar 20206366% male146102/44retrospective cohortIL-6Normal
Li-Da Chen (hen et al. (2020d)ChinaMar 20205250% male9469/25retrospective cohortIL-6, IL-2R, TNF-α, IL-8Normal
Lucía Guillén Guillén et al. (2020)SpainApr 20206273% male6449/15retrospective cohortIL-6Normal
Enrico Maria Trecarichi Trecarichi et al. (2020)ItalyMay 20208057.1% male4834/14retrospective cohortIL-6Normal
Elzbieta Rutkowska Rutkowska et al. (2021)PolandJan 20215656% male3823/15retrospective cohortIL-6Normal

Basic characteristics of 77 studies included in Meta-analysis.

Studies were published between December 2019 and June 2021. Among the 77 studies, 57 studies were performed in China, eight in Spain, three in Germany, three in Italy, two in Poland, and one each in Austria, the USA, France and Algeria. Seventy-three studies were published in normal journals, and four were published in preprint journals.14 cytokines were reported in these 77 studies, including IL-1β, IL-2, IL-2R, IL-4, IL-5, IL-6, IL-8, IL10, IL-15, IL-17, TNF-α, IFN-γ, MCP-1, and CXCL-10. Review Manager 5.3 was used to calculate and compare the sample mean and SD by the sample size and interquartile range. After removing the cytokines that having no statistical difference in either severe or death group, the cytokines that only contain two articles were also removed. Totally eight cytokines were included in our meta-analysis, containing IL-1β, IL-2R, IL-4, IL-6, IL-8, IL-10, IL-17, and TNF- α. Furthermore, we also screened the cytokines associated with gender or regions of COVID-19 patients. IL-2R, IL-6, IL-10 and TNF-α, which were correlated with gender or regions of COVID-19 patients, were finally presented in this study. All the included studies detected the serum levels of IL-6, while 13 studies focused on IL-2R, 31 studies analyzed IL-10 and 29 studies were related to the serum levels of TNF-α. Five studies analyzed IL-1β, 12 studies analyzed IL-4, 11 studies analyzed IL-8 and IL-17 was studies by four studies. Moreover, five studies analyzed the correlation between genders and cytokines. Fifty-seven and twenty-four studies analyzed the serum levels of cytokines in severity and mortality groups. All 77 studies had NOS quality scores greater than 6, indicating that all these studies have high levels of quality, as shown in Table 2.

TABLE 2

First authorStudy designSelectionComparabilityAssessment of outcomeTotal quality scores
Ai-Ping YangCohort*******7
Bo XuCohort********8
Changcheng ZhengCohort*******7
Changsong wangCohort********8
Chaomin WuCohort*******7
Chuan QinCohort*********9
Egon BurianCohort*******7
Fangfang LiuCohort*******7
Fei ZhouCohort*******7
Fengqin ZhangCohort********8
Guang ChenCohort*******7
Haijun WangCohort*******7
Han HuangCohort********8
Hong HuangCohort*********9
Hua FangCohort*******7
Huizheng ZhangCohort********8
Jia MaCohort*******7
Lang WangCohort*********9
Lei LiuCohort*********9
Lucas QuartuccioCohort*******7
Maria effenbergerCohort********8
María J. Pérez-SáezCohort*******7
Mario Fernández‐RuizCohort*********9
Marta CrespoCohort*******7
Miao LuoCohort********8
Michael DreherCohort********8
Ming NiCohort********8
Paola ToniatiCohort*******7
Pingzheng MoCohort*******7
Qin LuCohort*********9
Qiurong RuanCohort*******7
Ruirui WangCohort*******7
Shaohua LiCohort*******7
Sophie HueCohort********8
susu HeCohort*******7
Suxin WanCohort********8
Takahisa MikamiCohort********8
Tao ChenCohort********8
TAO LiuCohort********8
Tielong ChenCohort*******7
Tobias HeroldCohort*********9
Wenjun TuCohort********8
Xia XuCohort********8
Xiaohong YuanCohort********8
Xiong BeiCohort********8
Yang LiuCohort*******7
Yang XuCohort*******7
Yang Xu 2Cohort*********9
Yang ZhaoCohort********8
Yangjing XieCohort********8
Yanli WangCohort********8
Yaqing ZhouCohort********8
Yi LiCohort********8
Yi ZhengCohort*******7
Ying ChiCohort********8
Ying SunCohort********8
Yingjie WuCohort*********9
Yong GaoCohort********8
Zhe ZhuCohort******6
Zhihua LvCohort*********9
Zhilin ZengCohort********8
Zhongliang WangCohort********8
Elzbieta KalicinskaCohort*********9
Dianming LiCohort********8
Francisco Javier Gil-EtayoCohort********8
Feng GaoCohort********8
Wei ZhuCohort*******7
Zirui MengCohort********8
Chenze LiCohort*********9
Brahim BelaidCohort********8
Rocio Laguna-GoyaCohort*********9
Jose J. GuiraoCohort********8
Jose Marıa Galvan-RomanCohort*********9
Li-Da ChenCohort*******7
Lucía GuillénCohort*******7
Enrico Maria TrecarichiCohort********8
Elzbieta RutkowskaCohort********8

Methodological quality of the 77 studies based on the NOS for studies.

Proinflammatory Cytokines as the Driving Factor for Severity and High Mortality in COVID-19 Patients

To determine whether the circulating levels of inflammatory cytokines are risk factors for severity and mortality of COVID-19 patients, we classified the patients into mild and severe groups. There were 57 studies and 7,807 patients included in this meta-analysis. Compared to patients in the mild group, circulating levels of IL-6 was found to be significantly increased in patients in the severe group (19.76 [16.59, 22.93], p < 0.00001, Supplementary Figure S1). The serum level of IL-6 in the non-surviving group was also significantly elevated compared with that in the surviving group (52.33 [44.16, 60.50], p < 0.00001, Supplementary Figure S2). In addition to IL-6, the serum levels of IL-2R, IL-10, IL-1β, IL-4, IL-8, IL-17 and TNF-α were also elevated in both severe and non-surviving COVID-19 patients (Supplementary Figures S3–S6). Suggesting that the upregulation of these cytokines were correlated with the prognosis of COVID-19 patients.

Alterations of the Distinctive Cytokines Are Related to Sex Bias in COVID-19 Patients

In this meta-analysis, four cytokines were found to be correlated with severity of male COVID-19 patients. Five studies reporting circulating interleukin-6 (IL-6) levels in male (n = 488) and female (n = 509) COVID-19 patients were included. In addition, interleukin-2 receptor (IL-2R), interleukin-10 (IL-10) and tumor necrosis factor α (TNF-α) were also different between male and female patients. Compared to female patients, the expression levels of circulating IL-6 (11.76 [7.56, 15.96], p < 0.000001), IL-2R (85.75 [3.91, 167.59], p = 0.04), IL-10 (1.54 [0.99, 2.08], p < 0.00001) and TNF-α (1.39 [0.81, 1.97], p < 0.00001) were found to be significantly elevated in male patients (Figure 2). Additionally, we conducted a sensitivity analysis to confirm the robustness of the model, and a significant sex gap was detected in circulating levels of IL-6, IL-2R, IL-10 and TNF-α.

FIGURE 2

FIGURE 2

Forest plot for the male and female groups. The serum levels of IL-6 levels in the groups of male and female (A). The serum levels of IL-2R levels in the groups of male and female (B). The serum levels of IL-10 levels in the groups of male and female (C). The serum levels of TNF-α levels in the groups of male and female (D).

The Levels of IL-6 Related to Severity and High Mortality in COVID-19 Patients From Different Continents

We further analyzed the correlation between cytokines and continents. We classified the articles into Asia, Europe, Africa and North America groups, and there were 840 European patients, 6,910 Asian patients and 57 African patients in the selected studies. To better interpret the differences between countries, we compared the ages, sex distributions and the severe rate of the included patients in the two territories. Results showed that ages and the proportions of severe or dead patients were comparable, while the male patients in the severe COVID-19 patients in Europe was significantly higher than that in Asia (Supplementary Tables 1, 2). The results of our meta-analysis showed that Asian, European, and African patients with severe COVID-19 had elevated circulating IL-6 levels and the circulating IL-6 levels of European and African was higher than the Asian patients (Figure 3). Notably, we found that there were 997 Asian, 223 European, 19 African and 1007 North American in the analysis of mortality. Among them, all the death patients with COVID-19 had higher IL-6 levels than the survive patients. Moreover, Asian death patients still the have the lowest circulating IL-6 levels than the other continents’ patients (Figure 4). Unlike IL-6, the serum level of IL-10 had the potential to predict the risk of mortality in Asian patients, but it showed no correlation with mortality in European patients (Supplementary Figure S7).

FIGURE 3

FIGURE 3

The serum levels of IL-6 in the different continent of mild and severe.

FIGURE 4

FIGURE 4

The serum levels of IL-6 in the different continents of the alive and death.

Discussion

The SARS-CoV-2 S protein engages with the host ACE2 receptor and is subsequently cleaved at S1/S2 and S2′ sites by TMPRSS2 protease, which leads to activation of the S2 domain and drives fusion of the viral and host membranes. The secretion of interferon is the first step to start the antiviral program. Alveolar cells are an important part of the epithelial endothelial barrier. After respiratory epithelial cells were first infected by virus, virus infection activates pattern recognition receptors in these cells, triggering the production and release of type I and type III interferons (IFNs) and other proinflammatory mediators (such as cytokines, chemokines and antimicrobial peptides), so as to start the host’s innate and acquired immune response, which further activated the secondary cytokines (such as IL-10, IFN-γ, MCP-1, IL-4, and IL-17) and lead to cytokines storm (Vabret et al., 2020). In the mild patients, immune cells have the ability of eliminating viruses completely and inhibit the them from invading alveoli, which lead to low cytokines in serum (Figure 5). In this study, we identified that the serum levels of IL-6, IL-2R, IL-10, TNF-α, IL-1β, IL-4, IL-8 and IL-17 were significantly elevated in the severe or death cases and probably play crucial roles in the progression of COVID-19. Male sex was identified as a hazard for more severe disease and higher mortality in COVID-19 (Takahashi et al., 2020; Zeng et al., 2020). The recognition of how sex influences COVID-19 outcomes have important significance for clinical management and remission tactics. In this large-scale worldwide meta-analysis, the related cytokines affecting the development of severe disease in male patients were identified and the serum of IL-6, as well as IL-10, IL-2R and TNF-α, in males was obviously higher than that in females.

FIGURE 5

FIGURE 5

Increased circulating cytokines affect the development of COVID-19. The SARS-CoV-2 S protein engages with the host ACE2 receptor and is subsequently cleaved at S1/S2 and S2’ sites by TMPRSS2 protease. In the severe patients, COVID-19 invades the alveoli and activates innate immune responses to primary cytokines, such as type I and III IFNs, IL-6 and TNF-α, which further evokes the secondary cytokines and leads to cytokines storm. In the mild patients, immune cells have the ability of eliminating viruses and inhibiting them from invading alveoli, which leads to down-regulate cytokines in serum. 1The cytokines have significant differences between mild and severe groups. 2The cytokines between alive and death groups have significant differences. 3This cytokines have significant differences between male and female groups. 4This cytokines have significant differences between different regions.

IL-6, the core factor of “cytokine storm”, plays a pivotal role in the severity and high mortality of COVID-19. It enhances the production of TNF-α and IL-8 by stimulating the differentiation of T follicular helper cells, inhibits antiviral helper T cell 1 (Th1) cell commitment and improves the differentiation of helper T cell 2 (Th2) cells by regulating the circulating of IL-4 and interferon γ (IFN-γ) (Ahmadpoor and Rostaing, 2020; Wu and Yang, 2020). Moreover, elevated levels of IL-6 lead to acute lung injury and suppress the functions of T lymphocytes, macrophages and dendritic cells, which impair the immune system (Zhang et al., 2004). Tocilizumab, an IL-6 antagonist, revealed good capacity in inhibiting inflammation and cytokine storms in COVID-19 and various clinical studies have verified the beneficial effect of IL-6 and its receptor antagonists in treating severe and critical COVID-19 patients (Xu et al., 2020d; Potere et al., 2021). Besides IL-6, TNF-α inhibitor can also reduce lung exudation and inflammatory reactions, it has been used in the treatment of patients with covid-19 patients (Tirupathi et al., 2020b; Mackey et al., 2021b). However, blocking IL-6 and TNF-α inhibitor may not be used to all patients due to its potential adverse events and expensive price (Wang et al., 2020f; Keewan et al., 2021). The identification of which COVID-19 patients are suitable for treatment with IL-6 antagonists and TNF-α inhibitor are meaningful in the clinic. In our study, the cytokines IL-6, IL-10, and TNF-α were significantly upregulated in severe COVID-19 patients, especially in male patients, indicating that IL-6 antagonists and TNF-α inhibitors are more appropriate used in male patients to reduce both severity and mortality rate of COVID-19.

An increasing number of studies have pointed out that there are ethnicity-related differences in cytokines in systemic lupus erythematosus, chronic rhinosinusitis and other autoimmunity diseases (Niewold et al., 2012; Wang et al., 2016; Slight-Webb et al., 2020). We also focused on ethnicity-related differences in cytokines in COVID-19 patients and the results showed that there were lower circulating levels of IL-6 in Asian patients than in European and African patients, suggesting that IL-6 antagonists are recommended to use earlier in western countries.

This study had some limitations. Firstly, the articles that described the differential serum levels of cytokines in males and females were all from China. More clinical experiments should focus on the sex bias of cytokines in COVID-19. Secondly, our meta-analysis mainly investigated studies written in English, which might lead to language bias.

Conclusion

These large-scale data revealed that the serum levels of IL-6, IL-10, IL-2R, TNF-α, IL-1β, IL-4, IL-8, and IL-17 are potential risk factors for severity and high mortality in COVID-19. The IL-6 antagonist and TNF-α inhibitor are likely to be a proper therapeutic strategy to reduce mortality in males with COVID-19 and in Western countries.

Statements

Author contributions

HH wrote the manuscript, HP conceived and designed the study, HH and HP reviewed and revised the manuscript. HH and KH searched the database and extracted the data, HH and RL carried out the Meta-analysis and made figures, HP and HZ revised and sorted out the data, LL designed and performed the final review of the manuscript, all authors contributed to the article and approved the submitted version.

Funding

This work was financially supported by the National Key Research and Development Project of China (2020YFA0708003).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fphar.2022.802228/full#supplementary-material

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Summary

Keywords

COVID-19, cytokines, sex bias, mortality, meta-analysis

Citation

Hu H, Pan H, Li R, He K, Zhang H and Liu L (2022) Increased Circulating Cytokines Have a Role in COVID-19 Severity and Death With a More Pronounced Effect in Males: A Systematic Review and Meta-Analysis. Front. Pharmacol. 13:802228. doi: 10.3389/fphar.2022.802228

Received

26 October 2021

Accepted

13 January 2022

Published

14 February 2022

Volume

13 - 2022

Edited by

Andrzej Lange, Hirszfeld Institute of Immunology and Experimental Therapy (PAN), Poland

Reviewed by

Khalid Muhammad, United Arab Emirates University, United Arab Emirates

Ana Cristina Simões E. Silva, Federal University of Minas Gerais, Brazil

Soraya Mezouar, Aix-Marseille university, France

Updates

Copyright

*Correspondence: Liang Liu,

†These authors have contributed equally to this work

This article was submitted to Inflammation Pharmacology, a section of the journal Frontiers in Pharmacology

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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