Introduction

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), accounting for over 90% of all prostatitis diagnosis, affects approximately 2–15% of adult men in different countries [1, 2]. The considerable discomfort or pain of CP/CPPS reduces patients’ life quality significantly and lays a huge economic burden (e.g., the direct cost of CP/CPPS care is approximately $4000 a year per patient in USA) [3]. This is mainly ascribed to the complex etiologies and lack of effective treatments for CP/CPPS.

Recently, immune response and autoimmunity activation have been hypothesized to contribute to the development of CP/CPPS [4,5,6]. Several studies suggested that immune maladjustment led to the damage of self-tolerance to prostatic antigens and development of proinflammatory immune response [7,8,9]. However, most results are based on animal models; and the results from human studies based on semen and expressed prostatic secretions (EPS) sample are inconsistent. In this study, we investigated the differential expression of immune factors between the patients with CP/CPPS and the healthy volunteers, to gain further insights into the potential roles of immune mechanisms in the development of CP/CPPS.

Patients and methods

Patients and trial design

This study was registered in Australian New Zealand Clinical Trials Registry (ANZCTR) (Trial ID: ACTRN12613000792729) and approved by the Ethics Committee of Changhai hospital. Healthy volunteers and patients with CP/CPPS were enrolled in this study. All participants involved in this study signed the informed consent. Healthy volunteers were recruited from men who had routine health examination in our hospital and who had good physical health, while the patients with CP/CPPS were enrolled via outpatient urology consultation in the same period.

For CP/CPPS patients, the inclusion criteria were below: (a) aged 18–45 years old; (b) prostatitis-related syndrome longer than 3 months; (c) normal routine urine culture and negative bacterial culture in prostatic fluid. The exclusion criteria included: (a) CP/CPPS types I, II, or IV; and (b) the presence of other pelvic diseases that may explain the prostatitis-like symptoms; (c) history of bacterial prostatitis; (d) recent history of vaccination; (e) autoimmune disease; and (f) recent infections. For CP/CPPS patients, the symptom duration, treatment history, NIH-Chronic Prostatitis Symptom Index (NIH-CPSI) scores and EPS routine test were evaluated. Patients were further classified into two groups: types IIIA and IIIB CP/CPPS according to the results of EPS routine test. More than or equal to 10 leukocytes per high-power field in EPS were classified as type IIIA, and < 10 were classified as type IIIB. Before EPS collection, the patients were required to abstinence for more than 5 days. We also cleaned and disinfected patients’ penis and meatus before EPS collection.

Serum immune markers including IgA, IgM, IgG, CD4+ and CD8+ were assayed in both patients and healthy volunteers. We assayed CD4+ and CD8+ through flow cytometry using BD FACS CatoII with six-color TBNK kit (BD biosciences, USA). Immunoglobulin panel (IgA, IgM, IgG) was detected using Modular P (Roche, Switzerland). All the tests followed the manufacturers’ protocols.

Statistical analysis

SPSS Statistics 19 software was used for data processing. Statistical analysis was performed using Student t test and Mann–Whitney. Statistical significance was defined as p value < 0.05.

Results

A total of 23 CP/CPPS patients and 26 healthy volunteers were enrolled into the study. The age of patients and volunteers was 26.6 ± 3.4 and 26.8 ± 6.0 years, respectively (p > 0.05). The symptom duration time was 26 ± 9.4 months of CP/CPPS patients, and the NIH-CPSI score was 21.3 ± 4.4. None of the patients were taking a-receptor blockers for the treatment of CP/CPPS.

Of these 23 CP/CPPS patients, 12 patients were classified as having type IIIB CP/CPPS, while the other 11 patients had IIIA CP/CPPS. The serum levels of IgA, IgM, IgG, CD4+ and CD8+ in healthy volunteers and the patients are shown in Table 1. The serum levels of IgG were higher in CP/CPPS patients compared to healthy volunteers (1141.2 ± 204.3 vs 1031.9 ± 173.7 mg/L, p = 0.045), while the serum levels of CD8+ were lower in CP/CPPS patients compared to healthy volunteers (492.8 ± 185.6 vs 640.0 ± 246.8 cells/μL, p = 0.021).

Table 1 Differential level of serum markers in both CP/CPPS patients and healthy volunteers
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Furthermore, the serum levels of IgA, IgM, IgG, CD4+ and CD8+ were compared between patients with IIIA and IIIB CP/CPPS, and the results are shown in Table 2. Serum levels of IgG were higher in patients with IIIA CP/CPPS compared to those with IIIB (1244.3 ± 151.6 vs 1054.3 ± 209.3 mg/L, p = 0.023). However, there was no significant difference in IgA, IgM, CD4+ and CD8+ between the two groups.

Table 2 Differential level of serum markers between baseline patients with IIIA and IIIB CP/CPPS
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Discussion

The pathogenesis of CP/CPPS is unknown. Infection, trauma and stress have been reported to be involved in the development of CP/CPPS [4]. Although CP/CPPS has been considered as a bacterial chronic prostatitis, evidences showed that E. coli and helicobacter pylori antibodies can be detected in EPS and serum of those patients, respectively [4]. Furthermore, it has been reported that a strain of E. coli (strain CP1), isolated from the EPS of a CP/CPPS patient, could induce bacterial prostate colonization in non-obese diabetic (NOD) mice [10]. The pathogenesis CP/CPPS may be multifactorial, including infection, cell immune response, involvement of mast cells and activation of peripheral neurons. Thus, bacterial infection might play an important role in disease initiation, followed by cell immunity, activation of mast cells and peripheral neurons.

Recently, more studies have reported the roles of immune response and autoimmunity activation in the progression of CP/CPPS. In the murine models, CD4+ T cells, such as IFN-γ-producing Th1 cells and IL-17A-producing Th17 cells, could contribute to the development of pain even in the absence of a persistent bacterial infection [11]. Moreover, investigators further identified that mutations of insulin-dependent diabetes susceptibility 3 (IDD3) and cytotoxic T lymphocyte antigen 4 (CTLA4), both genes associated with the T-cell development and regulation, increase the risk of autoimmunity in experimental autoimmune prostatitis murine models [12, 13]. In addition, the loss of self-tolerized Treg cells and autoimmune regulator (AIRE) transcription factor might drive inflammation in CP/CPPS [14]. As a fact, TGF-β, TNF-α, IL-10, IL-6, MCP1 and MIP1a have been reported to be closely related to the development and progression of CP/CPPS [15].

Moreover, mast cells identified as the main mediator of Treg and Th17 cells have been reported to play an important role in regulation of cellular immunity with progression of prostatitis [16]. Activation of peripheral neurons responsible for chronic pelvic pain is also closely associated with mast cells [17, 18]. Despite the complex multifactorial etiology of CP/CPPS (infection, cell immune response, activation of mast cells and peripheral neurons), the cell immune response appears to be the core of multiple factors contributing to CP/CPPS. Nevertheless, the potential mechanism of cell immune involved in progression of CP/CPPS is still unknown.

In our study we investigated the differential serum levels of IgA, IgG, IgM, CD4+ and CD8+ in healthy volunteers and CPPS patients. These immune factors were chosen for analysis primarily because they are closely associated with autoimmunity and can be easily tested. Compared to healthy volunteers, we found that the CP/CPPS patients had lower serum levels of CD8+ and higher serum levels of IgG. It seems that both cell immunity and humoral immunity are involved in the development of CP/CPPS. These results suggested that immune-related mechanisms may be involved in CP/CPPS and immunomodulatory drugs may be tested as a potential treatment for CP/CPPS.

IgG is the most common type of serum antibodies in humans. It is widely distributed in respiratory, gastrointestinal and urogenital mucosa and protects the body from infection. However, the abnormal increase in IgG is associated with autoimmune diseases, such as autoimmune hepatitis and rheumatoid arthritis [19, 20]. Furthermore, previous articles also suggest that IgG can activate or enhance activation of mast cell and further induce proinflammatory cytokines expression and secretion, which is closely associated with inflammatory response [21, 22]. For CP/CPPS, distinguishing type IIIA from IIIB often confused us. Although we usually distinguish type IIIA and IIIB based on the amount of leukocytes in EPS, it may be artificial since both types show the increase of multiple differential proinflammation cytokines [23]. In this study, our results not only showed that the serum level of IgG was higher in CP/CPPS patients compared to healthy volunteer, but also is higher in IIIA compared to IIIB. So, maybe increased IgG plays important roles as an upstream inflammatory trigger in CP/CPPS. Although mast cell also could be activated through other signaling pathways [24], we think that the level of IgG could help us better distinguish between types IIIA and IIIB in clinical work.

A subset of CD8+ cells with the innate non-antigen-specific capabilities can lead to autoimmunity [25]. Moreover, mast cells could be activated to secrete chemokines, which could recruit effector CD8+ cells [26]. Thus, CD8+ are usually recruited to infected tissues via chemokines release [27]. Accordingly, histological examination of prostate inflammation shows increased numbers of CD8+ compared with normal controls [11, 28]. In this study, we further found decreased serum levels of CD8 + in CP/CPPS patients but no significant difference of serum levels of CD8+ between IIIA and IIIB. Obviously, the decreased level of CD8+ cells related to autoimmunity seems to contribute the progression of CP/CPPS. However, no further differential level of CD8+ cells between IIIA and IIIB suggests the possible involvement of cell immune based on CD8+ in both groups. Furthermore, a lack of the CD8+ level of prostate tissue hindered us from understanding the role of CD8+ in CP/CPPS. Anyhow, the detail mechanism needs further investigation.

There are several limitations of the study. First, the sample size is not large. Second, the normal reference levels of these immune factors in Chinese population were not yet established, even though we have demonstrated differences between CP/CPPS patients and healthy volunteers. Finally, we find immune factors involved in CP/CPPS but still need to further investigate the detail mechanism.

Conclusions

Differential levels of IgG and CD8+ between CP/CPPS patients and healthy volunteers suggest the contributing role of immune mechanisms to the development of CP/CPPS. The differential levels of IgG between patients with IIIA CP/CPPS and those with IIIB further indicate that humoral immune response based on IgG maybe plays a more important role in the inflammatory changes of CP/CPPS than cell immune response.