Lymphoma is a malignant tumour originating in the lymph nodes and/or extranodal lymphoid tissues. The main symptoms include painless lymphadenopathy, hepatosplenomegaly, accompanying whole-body and multiorgan reactions such as fever, wasting, drenching night sweats and itching (1). Myelosuppression often occurs in lymphoma patients who are treated with chemotherapy. During the myelosuppression stage, especially in the case of granulocytosis, patients have lower immunity and are prone to infection (2–4). Infection not only increases medical costs but also causes chemotherapy dose reductions, dose delays, or even treatment discontinuation that may result in prolonged hospitalization and reduced overall survival. Timely and effective anti-infective treatment is very important, and timely identification of infectious pathogens is critical for anti-infective efficacy. At present, the exact method for identifying pathogens is the cultivation of pathogenic bacteria (including blood culture, sputum culture and urine culture). However, it takes a certain length of time for the results of the cultivation of pathogenic bacteria, one or two days at least and as long as three or more days. Although elevated PCT and CRP usually indicate infection, G-/G+ infection cannot be distinguished. Therefore, it is necessary to find a new and faster method to identify G-/G+ infection.

Helper T (T helper, Th) cells have an important regulatory effect on the body’s immune system (5). Th can be divided into the TH1 subgroup and the TH2 subgroup under the stimulation of different antigens (6–8). Th1 cells mainly secrete IL-2 and IFN-γ (9, 10), which are involved in regulating cellular immunity, assisting the differentiation of cytotoxic T cells and participating in delayed hypersensitivity reactions. Th2 cells mainly secrete IL-4, IL-5, IL-6 and IL-10 (9–13), and their main function is to stimulate the proliferation of B cells and produce antibodies, which are related to humoral immunity and involved in the formation of immunosuppression, immune tolerance and rapid type hypersensitivity reactions. In recent years, it has been reported that Th1/Th2 cytokine changes play an important role in many infectious diseases (14, 15). Tang et al. used IL-6/IL-10 cytokines to identify G-/G+ bacteria in children with haematological diseases (15). However, there are few studies on the changes in THI/TH2 cytokines in adults with lymphomas who develop infection after chemotherapy. This study aims to quickly identify bacterial types through IL-6 and IL-10, select appropriate antibiotics in a timely manner, and understand the efficacy of anti-infection treatment through the trends of IL-6 and IL-10.

Lymphoma is a common haematological malignancy. Chemotherapy is one of the main treatments, but it may damage the immune system and lead to neutropenia, increasing patients’ susceptibility to infection. At present, clinicians often choose antibiotics according to the guidelines on granulocytosis with fever and clinical practice, which may lead to effective efficacy, overuse of antibiotics, emergence of drug-resistant bacteria, and even increase the economic burden of patients. Early and rapid diagnosis of infectious pathogens and timely application of appropriate antibiotics are essential. Early diagnosis and reasonable selection of antibiotics are essential to improve the prognosis of patients and prevent the abuse of antibiotics. The current gold standard for the diagnosis of pathogen types is pathogen culture, and second-generation sequencing can also identify pathogens. However, pathogen culture and second-generation sequencing generally take a long time, which is not conducive to early clinical diagnosis and treatment. The culture of pathogenic bacteria may result in false positives and false negatives. Moreover, second-generation sequencing is more expensive. Commonly used clinical infection markers, such as PCT and CRP, have certain limitations in the diagnosis of infection. The study showed that PCT has poor accuracy in distinguishing bacterial from nonbacterial infections, and PCT may not be an independent marker for the initiation of antibiotic therapy (16). CRP is often elevated in rheumatic connective tissue diseases. PCT and CRP have difficulty distinguishing G- and G+ infections. Therefore, it is urgent to find new and rapid indicators to distinguish G- and G+ infection.

In recent years, there have been some reports on the application of TH1/TH2 cytokines in infectious diseases (5, 11, 14, 17). Many studies have shown that IL-6 and IL-10 are related to infectious disease (18–20). Some scholars even found that IL-6/IL-10 could be used to identify G-/G+ bacterial infections in children (15). IL-6 is one of the newly discovered early markers to assist in the diagnosis of bacterial infections. IL-6 promotes the differentiation of B cells and the secretion of antibody proteins and induces the activation of cytotoxic T cells, thus enhancing immunity (21–23). IL-6 can induce the synthesis of acute-phase reactive proteins such as CRP in acute inflammation. This determination of IL-6 is helpful for the early evaluation and diagnosis of bacterial infection, and its sensitivity and specificity are higher than those of CRP in current clinical use. Its content has a good correlation with the development and prognosis of the disease (24, 25). IL-10 is a pleiotropic cytokine secreted by activated macrophages and T lymphocytes; and it has anti-inflammatory and immunosuppressive effects (22, 23, 26–28). IL-10 prevents the development of immunopathological damage caused by an overprotective immune response in acute and chronic infections. It is also responsible for the persistence of viruses and bacteria by interfering with innate and adaptive immune protection. This study was based on the detection of TH1/TH2 cytokines in peripheral blood based on flow cytometry (FCM). This technique has the advantages of high throughput, rapidity, and good reproducibility and is suitable for clinical analysis. With the progress of flow cytometry technology, CBA technology provides a powerful multichannel detection technology. Compared with the traditional enzyme-linked immunoadsorption assay (ELISA), the CBA method can quickly detect multiple cytokines, using lower sample sizes, labour costs and time consumption.

In this study, we found that there was no significant difference in IL-2 and IL-4 among the healthy, uninfected and infected groups. The INF-γ and TNF-α levels of lymphoma patients were higher than those of healthy controls. This may be because IFN-r and TNF-α are closely related to the occurrence and development of lymphoma, which is consistent with the results of a previous study (29, 30). We found that compared with healthy people and uninfected lymphoma patients, IL-6 and IL-10 were significantly increased in G- bacterial infections, while IL-6 was significantly increased and IL-10 was not significantly increased in G+ bacterial infections. The ROC value showed that IL-10 could distinguish between patients in the G- and G+ groups (Figure 1A, AUC = 0.904, P = 0.000). The cut-off value of IL-10 was 24.25 pg/mL, and its sensitivity and specificity were 87.8% and 84.6%, respectively. IL-6 could distinguish the infected group from the uninfected group (Figure 1B, AUC=0.990, P=0.000), the cut-off value of IL-6 was 53.20 pg/mL, and the sensitivity and specificity were 96.0% and 94.1%, respectively. However, since IL-6 showed no significant difference between the G- and G+ groups, it is obviously difficult for a single cytokine to distinguish G- and G+ bacterial infections in all populations. Combining the aforementioned ROC critical value, we named the approximately 10-fold increase in IL-6 and the 5-fold increase in IL-10 (IL-6>53.2 pg/ml and IL>24.25 pg/ml) as G- Bacterial Infection Cytokine Profile(G- BICP), and the approximately 10-fold increase in IL-6 and no more than the 5-fold increase in IL-10 (IL-6>53.2 pg/ml and IL ≤ 24.25 pg/ml) as G+ Bacterial Infection Cytokine Profile (G+ BICP). Tang et al. found that in childhood haematological tumours, IL-6 and IL-10 both increased by more than 10 times in G- bacterial infection, but the increase of the IL-10 was less than 10 times in G+ bacteria bacterial infection (15). This is consistent with the general direction of our research, but the value of IL-10 is slightly different, which may be related to the patient’s age and bone marrow suppression status after chemotherapy. Guan found that IL-6 and IL-10 were closely related to bloodstream infection and suggested that IL-10 might distinguish G- and G+ infection, but the diagnostic effect of IL-10 was not ideal, with a sensitivity of 64.1%. The specificity was 70.9% (31). Guan’s study did not observe the significance of the combination of IL-6 and IL-10 for the differentiation of G- and G+ infection, which may be caused by factors such as the different types of diseases of the study subjects (31). In this study, for the first time, we proposed the combination of IL-6 and IL-10 to identify G-/G+ bacterial infections in adult lymphoma during the myelosuppression stage after chemotherapy. The specificity and sensitivity of using IL-6 combined with the IL-10 cytokine to identify G- and G+ bacterial infections were both greater than 80%.

In addition, the present study found that PCT and IL-6 decreased gradually at day 4 and day 8 of treatment in the G- and G+ groups. A similar trend was reflected in the IL-10 level of the G- group. Some studies have shown that PCT can be used as an indicator of infectious diseases, infection severity and disease prognosis (32–34). However, a single PCT has some limitations, and other indicators often need to be combined in clinical practice (35). The present study suggested that dynamic monitoring of IL-6 and IL-10 can be used to evaluate the efficacy of anti-infective therapy, which is consistent with Guan’s research results (31). More observation time points were observed in this study for the changes in IL-6 and IL-10. Clinicians can preliminarily judge whether patients are infected and whether the infections are caused by G- or G+ bacteria; according to the cytokines, they can adjust antibiotic treatments in a timely manner and evaluate the effect of anti-infection treatment through dynamic monitoring of IL-6 and IL-10 changes.

In conclusion, this study suggests that cytokines, especially IL-6 and IL-10, can preliminarily identify lymphoma G-/G+ infections, which is conducive to early, timely and targeted selection of antibiotics. Il-6 and IL-10 can be used as indicators of anti-infection treatment effects. As a single-centre retrospective study, the present study has several limitations. The accuracy of IL-6/IL-10 in determining G-/G+ was less than 100%, and specific strains such as Escherichia coli or Klebsiella pneumoniae could not be identified. Although these results did not attain statistical significance, We observed that the IL-6 and IL-10 levels of the patients infected with Stenotrophomonas maltophilia were markedly higher than for the other groups of gram-negative bacteria. There were only 4 cases of stenotrophomonas maltophilia patients in our study. A larger sample size is needed in the future to investigate whether IL-6 and IL-10 levels are higher in patients infected with stenotrophomonas maltophilia than the patients infected with other gram-negative bacteria. In clinical practice, antibiotics should be selected according to cytokines, clinical symptoms, experience and guidelines.

The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding authors.

The studies involving human participants were reviewed and approved by the Ethics Committee of the First Affiliated Hospital of Guangdong Pharmaceutical University. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

QZ and HL conceptualized and designed the study. QZ, HL, and SZ collected and analyzed data. QZ drafted the paper. QZ, BW, ML, and XP carried out the data analysis, and revised the paper. All authors contributed to manuscript review, read, and approved the submitted version.

This study was supported by the Science and Technology Project of Yuexiu District of Guangzhou (2017-W S-008), the Natural Science Foundation of Guangdong Province (2017A030313664), and the Science and Technology Planning Project of Guangzhou (202002030253).

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.

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