The Predictive Value of Interleukin-6 and Neutrophil-Lymphocyte Ratio in Patients with Severe and Extremely Severe Oral and Maxillofacial Space Infections

Objective To investigate the correlation between clinical manifestation and neutrophil-lymphocyte ratio, C-reactive protein (CRP), and interleukin-6 (IL-6) in the patients with severe and extremely severe oral and maxillofacial space infection (OMSI). Methods In this retrospective study, we included 18 patients with severe and extremely severe OMSI from November 2012 to October 2018. Pearson or Spearman correlation coefficients were calculated to measure the association between the number of complications and locations and the number and percentage of lymphocyte, leukocyte, neutrophil, eosinophil, basophil, monocyte, CRP, and IL-6. A multivariable regression model was used to predict the number of complications and locations from these measures. Results IL-6 was positively correlated with neutrophil-lymphocyte ratio (rs = 0.773, P = 0.005), percentage of neutrophil (rs = 0.927, P = 0.001), and the number of neutrophil (rs = 0.627, P = 0.039). It was negatively correlated with percentage of monocyte (rs = −0.773, P = 0.005). CRP was positively correlated with neutrophil-lymphocyte ratio (rs = 0.556, P = 0.020) and percentage of neutrophil (rs = 0.515, P = 0.035). It was negatively correlated with the number of lymphocyte (rs = −0.517, P = 0.017), percentage of lymphocyte (rs = −0.578, P = 0.015), number of eosinophil (rs = −0.560, P = 0.020), percentage of eosinophil (rs = −0.504, P = 0.039), number of basophil (rs = −0.504, P = 0.039), and percentage of basophil (rs = −0.548, P = 0.023). The number of the involved organs was positively correlated with neutrophil-lymphocyte ratio (rs = 0.511, P = 0.030). The number of complications was positively correlated with the percentage of neutrophils (r = 0.738, P = 0.001), the neutrophil-lymphocyte ratio (r = 0.576, P = 0.012), IL-6 (rs = 0.907, P = 0.001), and CRP (rs = 0.599, P = 0.011). Multivariable regression analysis showed that the neutrophil-lymphocyte ratio (β = 0.080) was a significant predictor of the number of the involved organs and the neutrophil-lymphocyte ratio (β = 0.099). In addition, IL-6 (β = 0.002) was a significant predictor of the number of complications. Conclusions The neutrophil-lymphocyte ratio and IL-6 contributed to the assessment of general condition in severe and profound OMSI patients. These parameters can be used as predictors to evaluate the severity of OMSI.


Introduction
Oral and maxillofacial space infection (OMSI) usually occurs in the space between the oral, facial, and deep cervical parts, which is potentially associated with the infection in the loose connective tissues or the adipose tissues. According to the involved sites, scale, and the presence of airway obstruction, OMSI is classified into mild, moderate, severe, and extremely severe types. Generally, patients with severe OMSI present involvement in the parapharyngeal space, posterior pharyngeal space, and anterior tracheal space, while those with extremely severe OMSI presented mediastinal and intracranial infection. Severe OMSI is one of the types of deep cervical infection, which commonly complicates with acute respiratory obstruction, mediastinal inflammation, Lemierre's syndrome, suppurative thrombophlebitis of the internal jugular vein, cervical necrotizing fasciitis, and pneumonia [1]. Particularly, in the presence of patients with extremely severe OMSI, many would present poor prognosis due to descending necrotizing mediastinitis, which resulted in a mortality of up to 40% [2].
A large number of OMSI patients show host responses and humoral immunity, such as activation of complements, acute-phase proteins, cytokines, monocytes, macrophages, and anti-inflammatory mediators. Neutrophil plays an important role in the process of infectious disease [3]. Neutrophil and lymphocyte play an essential role in process of infection among the leukocyte subpopulation. In the process of infection, increasing neutrophil is a typical response of leukocyte [4]. Neutrophil-to-lymphocyte ratio (NLR) may more sensitive to indicate the extension of OMSI than other WBC subpopulations [5]. As an acute-phase protein, CRP is a rapidly elevated protein in the presence of infection, inflammation, and trauma [6]. As a proinflammatory cytokine, IL-6 was available in peripheral blood at the early stage of the infection, which then led to the generation of CRP in the liver. At the early stage, IL-6 level was higher than CRP level, which can be helpful to the early diagnosis [7]. To date, few studies focused on the prediction of the severe and extremely severe infections based on CRP, IL-6, or NRL. In this study, we aimed to investigate the correlation between these factors and the OMSI complications.

Patients.
In this retrospective study, we included 18 patients with severe and extremely severe OMSI from November 2012 to October 2018. Those with oral and maxillofacial space infection were included in this study. The exclusion criteria were as follows: patients with a history of antibiotic treatment of >10 days prior to admission, immunological diseases, abnormal liver and kidney functions, cancer patients, patients with alcohol or drug addiction, pregnant women, those with a BMI of >30, and those received hormones during treatment. Each patient signed the informed consent. The study protocols were approved by the Ethical Committee of the First Affiliated Hospital of Xinjiang Medical University.

Laboratory Examination.
The routine full and differential blood cell counts, CRP, and IL-6 of patients were tested within 2 h after admission. The blood samples were collected using tubes containing 5 ml anticoagulated venous blood (EDTA). The tube was centrifugated at 3,000 rpm for 10 min. The tested serological parameters included lymphocyte, leukocyte, neutrophil, eosinophil, basophil, monocyte (Beckman DxH 600 automated blood analyzer, USA), IL-6 (Liuyi WD-2102A, China), and C-reactive protein (Beckman AU5800, USA).

Statistical
Analysis. Data analysis was conducted using the SPSS 20.0 software. The Shapiro-Wilk method was utilized to verify the normality of the data. Data that were normally distributed were presented as the mean ± standard deviation. Data that were not normally distributed were presented as the median (P25, P75). Pearson correlation analysis was given to the dual variables that were normally distributed, and the Spearman correlation analysis was given to these that were not normally distributed. For missing values, listwise deletion was applied, and stepwise method was used for the multiple linear regression analysis. P < 0:05 was considered to be statistically significant.

Results
3.1. Patients' Characteristics. In total, 18 patients (male, 12; female, 6) diagnosed with severe and extremely severe OMSI were included in this study. They were in an age range of 16-75 years ðM, ½P25, P75 = 54, ½52, 59Þ. Based on the disease severity, there were 12 patients with severe OMSI and 6 patients with extremely severe OMSI. For the source of OMSI, 11 cases were of odontogenic infection and 7 cases of adenogenic infection ( Table 1).

Correlation between the IL-6 and CRP with Blood Values.
As shown in Table 3 (Table 3). Figure 1, the number of the involved organs showed a positive correlation with neutrophil-lymphocyte ratio (r = 0:511, P = 0:030). There were no differences with statistical significance for other WBC subpopulations, IL-6 and CRP (Table 4).  (Table 5).

Correlation between the Percentage of Neutrophils
3.6. Multiple Linear Regression Analysis of the Number of the Involved Organs. In this section, using the percentage of neutrophils and neutrophil-lymphocyte ratio as independent variables and the number of the involved organs as dependent variables in multiple linear regression analysis, stepwise regression was carried out in one step. Adjusted coefficient of determination (R adj 2 ) of the models was 0.225. Therefore, it was the optimal equation (F = 5:949, P = 0:027). The fitted regression equation was statistically significant. Importantly, neutrophil-lymphocyte ratio was found to be a statistically       (Table 6). However, the mean of studentized residual was -2.256 to 2.520 and Cook's distance was 0.001 to 1.467 with 18 objectives.

Multiple Linear Regression Analysis of the Number of
Complications. In this section, using the percentage of neutrophils, neutrophil-lymphocyte ratio, IL-6, and CRP as independent variables as well as the number of complications as dependent variables in multiple linear regression analysis, stepwise regression was carried out in 4 steps. Adjusted coefficient of determination (R adj 2 ) of the two models was 0.904.
Therefore, it was the optimal equation (F = 47:912, P = 0:001 ). The fitted regression equation was statistically significant. Importantly, the neutrophil-lymphocyte ratio and IL-6 were significant predictors for the number of complications (Table 7). However, the mean of studentized residual was -1.261 to 1.561 and Cook's distance was 0.006 to 10.132 with 11 objectives.

Discussion
OMSI is a common disease in oral and maxillofacial regions. These patients may show complications or even lifethreatening conditions, in the absence of appropriate treatment. To date, extensive studies have been conducted to screen the potential markers in order to distinguish highrisk and low-risk space infections. Neutrophil-lymphocyte ratio (NLR) was positively correlated with the number of infection sites in patients with severe OMSI. Patients with more infection sites usually showed higher neutrophil-lymphocyte ratio. Neutrophils have been considered one of the main factors involving in the innate immune response, as they present antibacterial and cytotoxic effects, as well as multiple immunomodulatory functions such as proinflammatory and anti-inflammatory effects [4,8]. These indicated that percentage of neutrophils contributed to the estimation of the infection sites of the OMSI patients.
NLR, as an infectious parameter which is easy and quick to get, is an indicator for imbalance of systemic cell-mediated immunity [9]. It reported that NLR assisted in predicting the prognosis of infectious disease [10][11][12]. However, NLR was considered to be an indicator for some infectious tumor and cardiovascular diseases [13][14][15].
In our study, the number of the involved organs showed a positive correlation with neutrophil-lymphocyte ratio. The multiple linear regression analysis showed that a higher NLR was a significant predictor of more involved organs. As the sample size for patients with severe and extremely severe OMSI was small, there might be possibilities of data missing and outliers. Above all, the results should be interpreted rationally, and more cases should be integrated in the subsequent study. In future, more studies are required to investigate the effectiveness of the NLR.
Neutrophils and lymphocytes play essential roles in immune responses [16,17]. In the presence of physical or   [17,18]. Because neutrophil-to-lymphocyte ratio is calculated as neutrophil count divided by lymphocyte count, it can reflect the changes in both types of cells. Therefore, it is considered a more sensitive marker for the evaluation of extent of stress or systemic inflammation than the other cell type alone such as neutrophils and lymphocytes [16]. Our data indicated a positive correlation between the neutrophil-lymphocyte ratio, IL-6, and complications in patients with severe and extremely severe OMSI. In multivariable regression analysis, both neutrophil-lymphocyte ratio and IL-6 entered the equation, and coefficient of determination adjusted coefficients was 0.904. The neutrophillymphocyte ratio and IL-6 were the main independent predictors for the number of complications. Previous studies suggested that complications in OMSI patients were associated with blood glucose, WBC count, systemic disease, neck swelling, and disease duration [8,19,20]. The serious complications were related to the pathogenesis of diabetes, multiple space infection, number of WBCs upon admission (≥1:5 × 10 9 /l), age (≥65 years), history of medication, dyspnea, and body temperature (>39°C) [21][22][23]. Percentage of neutrophils was an independent predictor for serious complications. In addition, there was an association between percentage of neutrophils of >85% and the severity of maxillofacial space infection [16]. Patients with a high percentage of neutrophil-lymphocyte ratio and IL-6 at admission should be alert about the severity of complications in order to control the condition effectively and avoid the occurrence of serious complications. However, in this study, the cook's distance was greater than 0.5 and absolute value of the studentized residuals was greater than 2 from multiple linear regression analysis. On this basis, there might be outliers in these formulas. Neutrophil-lymphocyte ratio and IL-6 should be still tested in further studies, together with illustrating the influence to the complications.
There are some limitations in this study. As the number of cases diagnosed with severe and extremely severe OMSI combined with life-threatening complications is limited, it is difficult to extend to all patients with maxillofacial space infections. The follow-up should expand the scope of application and the sample content. Meanwhile, the blood test indices were not adequate for each patient. In future, more studies involving a large sample size are needed.
In summary, the neutrophil-lymphocyte ratio and IL-6 contributed to assessment of general condition in severe and extremely severe OMSI patients. These parameters could be utilized as predictors to evaluate the severity of OMSI in clinical settings.

Data Availability
All the data are available upon appropriate request.

Conflicts of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.