Introduction
Obesity is increasing, global health problem [1]. An excessive amount of adipose tissue is a major risk factor for cardiovascular, metabolic, and musculoskeletal diseases as well as cancer. Moreover, the adipose tissue being endocrine active alters the inflammatory and immunological response [2, 3]. Recently, it was reported that surgical intervention affects local and systemic immune responses, particularly in obese individuals [4]. Laparoscopic technique, due to its minimal invasiveness, is considered to preserve immune function. Nevertheless, the immunological consequences of laparoscopic surgeries are still not entirely described [5, 6].
Dendritic cells (DCs) are the most potent antigen-presenting cells (APCs), which are able to initiate and regulate immunological responses [7]. There are at least two well-characterized subsets of circulating DCs: myeloid DCs (BDCA-1+ and CD19–) and lymphoid DCs (BDCA-2+ and CD123+) [8]. Many studies have attempted to evaluate immunological response to surgical trauma. Surgery changes the quantity and phenotype of circulating blood DCs, including a decrease of total DCs post-operatively [9-11].
The present study aimed to evaluate the percentage and changes of the myeloid (BDCA-1+ and CD19–), lymphoid (BDCA-2+ and CD123+) cells, and the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) in obese and normal weight patients undergoing laparoscopy.
Material and methods
Study population
The study enrolled patients with cholelithiasis admitted to the General and Oncological Surgery Department of the District Specialist Hospital of Lublin, Poland. The study group consisted of 60 asymptomatic patients with gallstones shown by ultrasound examination. Patients with ultrasounds’ signs of gallbladder complications (e.g., empyema, hydrops, wall necrosis, jaundice, and other), symptoms of acute cholecystitis, and a history of diabetes and immunologic disorders or allergies were excluded.
All the patients underwent laparoscopic cholecystectomy with standard values of carbon dioxide pneumoperitoneum (12-14 mm Hg). The patients underwent surgery performed via a four-trocar technique. After recognition of Calot’s triangle, the cystic duct and cystic artery were clipped and cut. Gallbladder was removed with a medical protector through an incision below the umbilicus. In each case, the gallbladder was evaluated by pathologic examination, and no malignancy was observed. No complications during the early post-operative period were reported. All the patients were informed about the aims of the study, and a written consent was obtained from each patient. The study was approved by the Ethical Committee at the Medical University of Lublin (decision No. KE-0254/240/2008).
Patients were divided into two groups according to body mass index (BMI): group N (n = 29, BMI ≤ 25 kg/m<sup>2</sup>) and group O (n = 31, BMI > 30 kg/m<sup>2</sup>).
Blood collection, preparation, and flow cytometric evaluation
Blood samples were obtained before the surgery as well as 24 and 48 hours after the procedure. Mononuclear cells were separated on lymphocyte separation medium – Gradisol L (Aqua Med, Poland) and centrifuged for 20 minutes at 700 × g. Every 107 of mononuclear cells were incubated with 10 µl of FcR – blocking reagent (Miltenyi Biotec, Germany) for 5 minutes to avoid non-specific binding and labeled with monoclonal antibodies against following antigens: BDCA-1, BDCA-2, and CD19. After incubation, cells were centrifuged and washed for 5 minutes at 700 × γ in 4 degrees of Celsius. The myeloid dendritic cells: anti – BDCA-1 (CD1c) FITC (Miltenyi Biotec, Germany) and anti – CD19 CyChrome (Becton Dickinson, USA). The lymphoid dendritic cells: anti – BDCA-2 (Miltenyi Biotec, Germany) and CD123 PE (Becton Dickinson, USA). The cells were collected using a FACSCalibur flow cytometry (Becton Dickinson, USA) and the phenotypes were analyzed with CellQuest software (Becton Dickinson, USA). For each analysis, 300,000 of events were collected. Cell debris and dead cells were excluded based on scatter signal. The fluorescence-minus-one method or the unstained cell were applied as negative control.
Statistical analysis
Statistical analysis was performed using 16.0 SPSS software (SPSS, Chicago, IL, USA). Differences between studied patients’ populations were assessed using the Mann-Whitney U test. Differences from baseline within each group were evaluated with the Wilcoxon matched-pairs signed-ranks test. All p-values lower than 0.05 were considered significant.
Results
Patients population
The patients were assigned into two study groups. Group N consisted of 29 patients (M : F ratio = 15 : 14), while group O included 31 patients (M : F ratio = 16 : 15). The median age of patients was 53 and 55 years, respectively, in group N and O. The groups differed significantly (p < 0.001) in terms of BMI. In group N, BMI was 23.15 kg/m<sup>2</sup> (range, 18.45-24.73 kg/m<sup>2</sup>) and in group O, it was 31.35 kg/m<sup>2</sup> (range, 30.02-39.40 kg/m<sup>2</sup>). There were no statistically significant differences between the two study groups in terms of duration of the surgery (45.40 min in group N and 51.02 min in group O), and hematological and biochemical parameters assessed before and after the surgery. The median body temperature, white blood counts (WBC), and C-reactive protein (CRP) were similar in both study groups post-operatively. No complications (e.g., fever, wound infection) were observed during post-operative period in all studied patients.
Circulating DCs subsets in obese and normal-weighted patients before and after the surgery
The percentage of myeloid (BDCA-1+ and CD19–), lymphoid (BDCA-2+ and CD123+) cells, and the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) was analyzed in three times points in both study groups. There were no statistically significant differences between obese and normal-weighted patients before (pre-OP), and at 24 and 48 hours after the surgery, except the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) assessed in the 48-post-operative hour. The results are presented in Table 1.
Table 1
Percentages of myeloid (BDCA-1+ and CD19–) and lymphoid (BDCA-2+ and CD123+) cells, and the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) in peripheral blood of patients in both studied groups at three time points
Post-operative changes of circulating DCs subsets
The percentage of myeloid (BDCA-1+ and CD19–), lymphoid (BDCA-2+ and CD123+) cells as well as the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+and CD123+) was determined in three time periods (Table 2). In group N and O, we did not observe significant changes in the percentage of the myeloid DCs at post-OP 24 h compared to pre-OP baseline level. However, the myeloid DCs percentage increased significantly at post-OP 48 h compared to post-OP 24 h and pre-OP baseline in both studied groups. The percentage of lymphoid DCs increased significantly in group O in all studied time periods, while in group N, the only one significant change was observed at post-OP 24 h compared to pre-OP baseline level. In group N, the myeloid DCs to lymphoid DCs ratio significantly increased at post-OP 48 h compared to post-OP 24 h. In group O, the myeloid DCs to lymphoid DCs ratio increased significantly at post-OP 24 h compared to pre-OP baseline levels.
Table 2
Changes of the percentage of myeloid (BDCA-1+ and CD19–) and lymphoid (BDCA-2+ and CD123+) cells, and the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) in peripheral blood of patients in both studied groups at three time periods
Discussion
Nowadays, minimally invasive surgical techniques have become a standard in the treatment of numerous diseases affecting almost all body system [12]. Even though laparoscopy is considered to reduce tissue damage when compared to open surgery, it is still followed by activation of immune system at both local and systemic levels [5, 6]. The response to surgery could be impaired in obese individuals [2,4]. Adipose tissue is recognized as a significant endocrine organ [13]. It houses inflammatory cells and secretes active mediators of inflammation, including adiponectin, leptin, interleukin 6 (IL-6), and tumor necrosis factor-a (TNF-α) [3, 14].
Our investigation did not show significant differences in the percentage of the myeloid (BDCA-1+ and CD19–), lymphoid (BDCA-2+ and CD123+) cells, and the myeloid to lymphoid cells ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) before and after the surgery in obese compared to normal-weight patients. To date, researches have not been focusing on the evaluation of DCs’ populations in human adipose tissue. However, several studies have described the effects of adipocyte and adipocyte-derived factors on myeloid cells, and have identified and phenotype different subsets of DCs in human subcutaneous adipose tissue, which could not be translated to visceral adipose tissue [15-17]. Based on murine models, authors suggested a role of DCs, particularly conventional DCs, in the promotion of low-grade inflammation in adipose tissue [18]. Despite compelling evidence, the role of DCs in the adipose tissue remains unclear and requires further investigations. The percentage of myeloid and lymphoid DCs in the peripheral blood was evaluated by Nickel et al. [19]. Authors described the lower expression of myeloid DCs in obese compared to lean individuals, while the percentage of lymphoid DCs was in opposite: it was higher in obese than in normal weight persons. Differences in expression of circulating myeloid and lymphoid DCs in normal weight and obese individuals suggest that excessive amount of adipose tissue modifies the immune system. However, the exact mechanism and direction of this modulation are not fully understood.
We observed a significant increase of the percentage of myeloid (BDCA-1+ and CD19–) DCs in the early post-operative period in both study groups. However, the tendency to higher increase of DCs’ percentage was typical for obese patients. The percentage of lymphoid DCs (BDCA-2+ and CD123+) increased significantly in the early post-operative period in obese compared to normal weight patients. However, in the first 24 post-operative hours, an increase of lymphoid DCs was also observed in normal weigh patients. Lymphoid DCs are considered to display a dual function of Ag-capturing and potent inhibition of IFN-α/β induction [20]. The significant increase of lymphoid DCs might cause skewing T cell responses towards a non-Th1 type of response and therefore, decrease of Th1 polarization and weaker response to intracellular pathogens [21, 22]. Our results are in contrast with the study of Ho et al., who monitored changes in DCs counts in patients undergoing laparoscopic cholecystectomy [23]. They observed a significant increase of DCs count intraoperatively compared to the level before the surgery; however, in the post-operative period, the DCs counts significantly decreased.
The myeloid to lymphoid DCs ratio (BDCA-1+ and CD19–/BDCA-2+ and CD123+) in the peripheral blood might revealed the imbalance of Th1 and Th2 polarization [20, 21]. After surgery, higher myeloid to lymphoid DCs ratio can suggest Th1 polarization, activation of cytotoxic cells, and leads to tissue damage and formation of intraperitoneal adhesions. By contrast, low post-operative myeloid to lymphoid DCs ratio favor humoral response and promotes elimination of bacterial infections and development of immunological tolerance.
In our study, we did not observe significant differences in the myeloid to lymphoid DCs ratio between study groups. In the first 24 post-operative hours, the myeloid to lymphoid DCs ratio significantly decreased in obese patients. It suggests a stronger activation of lymphoid than myeloid DCs due to surgical trauma.
Conclusions
Laparoscopy induces immunomodulation, such as changes of myeloid and lymphoid dendritic cells, especially in obese patients. We describe new findings, in which minimally invasive surgical trauma promotes the increase of percentage of circulating DCs in the early post-operative period. Future studies are required to greatly investigate the role of an excessive amount of adipose tissue on peripheral blood DCs and immune response in patients undergoing surgeries.
