Expression of IL-27 by tumor cells in invasive cutaneous and metastatic melanomas [corrected]

IL-27 in combination with anti-PD-1 can be anti-cancer or pro-cancer

Interleukin-27 (IL-27) is known to play opposing roles in immunology. The present paper considers, specifically, the role IL-27 plays in cancer immunotherapy when combined with immune checkpoint inhibitor anti-PD-1. We first develop a mathematical model for this combination therapy, by a system of Partial Differential Equations, and show agreement with experimental results in mice injected with melanoma cells. We then proceed to simulate tumor volume with IL-27 injection at a variable dose F and anti-PD-1 at a variable dose g. We show that in some range of "small" values of g, as f increases tumor volume decreases as long as fFc(g), where Fc(g) is a monotone increasing function of g. This demonstrates that IL-27 can be both anti-cancer and pro-cancer, depending on the ranges of both anti-PD-1 and IL-27.

Interleukin-27 potentiates CD8+ T-cell-mediated antitumor immunity in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) cells are highly dependent on interactions with the immunosuppressive tumor microenvironment (TME) for survival and proliferation. In the search for novel treatments, pro-inflammatory cytokines have emerged as candidates to reactivate the immune system. Among those, interleukin 27 (IL-27) has recently gained attention, but its effects differ among malignancies. Here, we utilized the Eμ-TCL1 and EBI3 knock-out mouse models as well as clinical samples from patients to investigate the role of IL-27 in CLL. Characterization of murine leukemic spleens revealed that the absence of IL-27 leads to enhanced CLL development and a more immunosuppressive TME in transgenic mice. Gene-profiling of T-cell subsets from EBI3 knock-out highlighted transcriptional changes in the CD8+ T-cell population associated with T-cell activation, proliferation, and cytotoxicity. We also observed an increased anti-tumor activity of CD8+ T cells in the presence of IL-27 ex vivo with murine and clinical samples. Notably, IL-27 treatment led to the reactivation of autologous T cells from CLL patients. Finally, we detected a decrease in IL-27 serum levels during CLL development in both pre-clinical and patient samples. Altogether, we demonstrated that IL-27 has a strong anti-tumorigenic role in CLL and postulate this cytokine as a promising treatment or adjuvant for this malignancy.

Crosstalk between macrophages and natural killer cells in the tumor microenvironment

The tumor microenvironment (TME) is jointly constructed by a variety of cell types, including tumor cells, immune cells, fibroblasts, and epithelial cells, among others. The cells within the TME interact with each other and with tumor cells to influence tumor development and progression. As the most abundant immune cells in the TME, macrophages regulate the immune network by not only secreting a large amount of versatile cytokines but also expressing a series of ligands or receptors on the surface to interact with other cells directly. Due to their strong plasticity, they exert both immunostimulatory and immunosuppressive effects in the complex TME. The major effector cells of the immune system that directly target cancer cells include but are not limited to natural killer cells (NKs), dendritic cells (DCs), macrophages, polymorphonuclear leukocytes, mast cells, and cytotoxic T lymphocytes (CTLs). Among them, NK cells are the predominant innate lymphocyte subsets that mediate antitumor and antiviral responses. The activation and inhibition of NK cells are regulated by cytokines and the balance between activating and inhibitory receptors. There is an inextricable regulatory relationship between macrophages and NK cells. Herein, we systematically elaborate on the regulatory network between macrophages and NK cells through soluble mediator crosstalk and cell-to-cell interactions. We believe that a better understanding of the crosstalk between macrophages and NKs in the TME will benefit the development of novel macrophage- or NK cell-focused therapeutic strategies with superior efficacies in cancer therapy.

IL-27, a pleiotropic cytokine for fine-tuning the immune response in cancer

Interleukin (IL)-27, a member of the IL-6/IL-12 family, has an important role in modulating inflammation in partnership with innate and adaptive immune cells. IL-27 binding to IL-27R starts downstream signaling based on the target cells. It can instigate inflammation by inducing CD4⁺ T cell proliferation, Th1 polarization, cytotoxic T cell activation, generation of the natural killer cell, and macrophage and dendritic cell activation. However, by inducing programmed cell death and suppression of effector cells, IL-27 can suppress inflammation and return the immune response to hemostasis. Altogether, IL-27 displays multifaceted dual functions, which may result in either pro- or anti-inflammatory effects. Recent investigations indicated the antitumor activity of IL-27 via inducing Th1, and CTL responses and generating NK cells. On the other hand, IL-27 also can promote tumor cells' proliferation, survival, and angiogenesis. In the present review, we'll discuss recent advances concerning the role of IL-27 in inflammatory diseases such as infections, autoimmune diseases with a focus on cancer.

Interleukin-27 is abrogated in gastric cancer, but highly expressed in other Helicobacter pylori-associated gastroduodenal diseases

BACKGROUND

IL-27 has dual roles in the immune response either stimulating Th1 or inhibiting Th17 cells. Because there is a particular link of IL-23/Th17 axis in the development of cancer and IL-27 has been considered a potential treatment for cancer, we evaluated the gastric and serum concentrations of IL-27 in two mutually exclusive Helicobacter pylori-associated diseases, gastric cancer (GC) and duodenal ulcer (DU).

MATERIAL AND METHODS

We prospectively studied 110 H pylori-positive patients and 40 healthy blood donors. Serum and gastric concentrations of IL-27 and cytokines of the Th1/Th17 cells were assessed by ELISA.

RESULTS

IL-27 was not detected in GC patients, but the cytokine concentration was very high in the patients with DU. IL-27 was also detected in the gastritis patients and in the H pylori-positive blood donors. IL27RA mRNA expression in peripheral blood mononuclear cells, evaluated by rt-PCR, was stimulated by H pylori strains. The cytokine concentration positively correlated with the Th1 and negatively with Th17 cell representative cytokine levels. Gastric IL-27 concentrations were positively correlated with increased degree of mononuclear and polymorphonuclear cells on the antral gastric mucosa of DU patients in consonance with the DU gastritis pattern. IL-12p70 and IFN-γ gastric concentrations were significantly higher in DU than in GC. Conversely, gastric concentrations of Th17 cell-associated cytokines (IL-1β, IL-6, IL-17A, IL-23, and TGF-β) were significantly higher in GC than in DU patients.

CONCLUSION

Although H pylori infection is able to elicit IL-27 and IL-27Rα secretion, DU and GC have diametrically opposed cytokine patterns.

IL-27, IL-30, and IL-35: A Cytokine Triumvirate in Cancer

The role of the immune system in anti-tumor immunity cannot be overstated, as it holds the potential to promote tumor eradication or prevent tumor cell escape. Cytokines are critical to influencing the immune responses and interactions with non-immune cells. Recently, the IL-12 and IL-6 family of cytokines have accumulated newly defined members each with specific immune functions related to various cancers and tumorigenesis. There is a need to better understand how cytokines like IL-27, IL-30, and IL-35 interact with one another, and how a developing tumor can exploit these interactions to enhance immune suppression. Current cytokine-based immunotherapies are associated with cytotoxic side effects which limits the success of treatment. In addition to this toxicity, understanding the complex interactions between immune and cancer cells may be one of the greatest challenges to developing a successful immunotherapy. In this review, we bring forth IL-27, IL-30, and IL-35, “sister cytokines,” along with more recent additions to the IL-12 family, which serve distinct purposes despite sharing structural similarities. We highlight how these cytokines function in the tumor microenvironment by examining their direct effects on cancer cells as well their indirect actions via regulatory functions of immune cells that act to either instigate or inhibit tumor progression. Understanding the context dependent immunomodulatory outcomes of these sister cytokines, as well as their regulation within the tumor microenvironment, may shed light onto novel cancer therapeutic treatments or targets.

Interleukin-27 and interleukin-35 in de novo acute myeloid leukemia: expression and significance as biological markers

BACKGROUND AND OBJECTIVES

IL27 and IL35 are regulatory T cells (T-regs) related cytokines; they were accused in eukemogenesis of acute myeloid leukemia (AML). This study aimed to assess the expression of these cytokines in de novo AML and investigate their role as biomarkers.

SUBJECTS AND METHODS

Seventy newly diagnosed patients with primary AML and 30 matched healthy volunteers were recruited. AML diagnosis was confirmed with flowcytometric and immunophenotypic analyses, while ELISA was used to assess serum levels of IL27 and IL35 in patients and controls. Receiver operating characteristic curve analysis was used to estimate IL27 and IL35 optimum cutoff values for predicting AML.

RESULTS

Serum levels of both cytokines were significantly higher in AML patients than controls (P<0.001), with no effect of gender or French-American-British subtypes. Significant correlations of IL27 and IL35 with poor prognostic factors and with each other were detected in patients only. IL27 optimum cutoff for predicting AML was >43, AUC (0.926) with a sensitivity 74% and specificity 96.6% (P<0.001), while for IL35>27.8, AUC (0.972) with 88% and 98% sensitivity and specificity, respectively (P<0.001).

CONCLUSION

Conclusively, this study proved that IL27and IL35 could identify AML patients from healthy subjects, and their overexpression denotes poor prognosis. Based on the simplicity and wide availability of their detection technique we recommend the inclusion of IL27 and IL35 in the diagnostic/prognostic workup of AML; however, further longitudinal research is needed to prove their exact prognostic value.

Investigation of Interleukin-27 in the Sera of Nonmelanoma Skin Cancer Patients

IL-27 has been shown to have both tumor promoting and suppressing functions. IL-27, with its diverse influences on immune responses, has not been studied extensively in nonmelanoma skin cancers (NMSC), including Squamous and Basal Cell Carcinomas (SCC and BCC), and its roles in tumor initiation, progression, and its probable use in NMSC treatment have yet to be unveiled. A cross-sectional analytical study was designed to investigate the serum levels of IL-27 in NMSC patients in comparison to normal individuals. Levels of IL-27 in the sera of 60 NMSC patients along with 28 healthy controls were measured by means of quantitative enzyme-linked immunosorbent assay (ELISA). In this study we observed that IL-27 serum levels were significantly higher in NMSC patients in comparison to healthy individuals (0.0134 versus 0.0008 ng/ml; P<0.001). Furthermore, when subcategorized based on pathological diagnosis, both BCC and SCC patients had higher levels of IL-27 in their sera compared to controls (P=0.002 and P=0.033; respectively). However, these levels were not different among SCC and BCC patients. According to our results, it seems that IL-27 is involved in antitumor immune responses in NMSCs. On the other hand, these observations might be indicative of this cytokine involvement in NMSC tumorigenesis and progression. Therefore, administration of this cytokine for therapeutic purposes in patients with such conditions should be erred on the side of caution.

Levels of peripheral blood polymorphonuclear myeloid-derived suppressor cells and selected cytokines are potentially prognostic of disease progression for patients with non-small cell lung cancer

Polymorphonuclear-MDSC (PMN-MDSC) have emerged as an independent prognostic factor for survival in NSCLC. Similarly, cytokine profiles have been used to identify subgroups of NSCLC patients with different clinical outcomes. This prospective study investigated whether the percentage of circulating PMN-MDSC, in conjunction with the levels of plasma cytokines, was more informative of disease progression than the analysis of either factor alone. We analyzed the phenotypic and functional profile of peripheral blood T-cell subsets (CD3+, CD3+CD4+ and CD3+CD8+), neutrophils (CD66b+) and polymorphonuclear-MDSC (PMN-MDSC; CD66b+CD11b+CD15+CD14-) as well as the concentration of 14 plasma cytokines (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12 p70, IL-17A, IL-27, IL-29, IL-31, and IL-33, TNF-α, IFN-γ) in 90 treatment-naïve NSCLC patients and 25 healthy donors (HD). In contrast to HD, NSCLC patients had a higher percentage of PMN-MDSC and neutrophils (P < 0.0001) but a lower percentage of CD3+, CD3+CD4+ and CD3+CD8+ cells. PMN-MDSC% negatively correlated with the levels of IL1-β, IL-2, IL-27 and IL-29. Two groups of patients were identified according to the percentage of circulating PMN-MDSC. Patients with low PMN-MDSC (≤ 8%) had a better OS (22.1 months [95% CI 4.3-739.7]) than patients with high PMN-MDSC (9.3 months [95% CI 0-18.8]). OS was significantly different among groups of patients stratified by both PMN-MDSC% and cytokine levels. In sum, our findings provide evidence suggesting that PMN-MDSC% in conjunction with the levels IL-1β, IL-27, and IL-29 could be a useful strategy to identify groups of patients with potentially unfavorable prognoses.

The PD-L1- and IL6-mediated dampening of the IL27/STAT1 anticancer responses are prevented by α-PD-L1 or α-IL6 antibodies

Interleukin-27 (IL27) is a type-I cytokine of the IL6/IL12 family and is predominantly secreted by activated macrophages and dendritic cells. We show that IL27 induces STAT factor phosphorylation in cancerous cell lines of different tissue origin. IL27 leads to STAT1 phosphorylation and recapitulates an IFN-γ-like response in the microarray analyses, with up-regulation of genes involved in antiviral defense, antigen presentation, and immune suppression. Like IFN-γ, IL27 leads to an up-regulation of TAP2 and MHC-I proteins, which mediate increased tumor immune clearance. However, both cytokines also upregulate proteins such as PD-L1 (CD274) and IDO-1, which are associated with immune escape of cancer. Interestingly, differential expression of these genes was observed within the different cell lines and when comparing IL27 to IFN-γ. In coculture experiments of hepatocellular carcinoma (HCC) cells with peripheral blood mononuclear cells, pre-treatment of the HCC cells with IL27 resulted in lowered IL2 production by anti-CD3/-CD28 activated T-lymphocytes. Addition of anti-PD-L1 antibody, however, restored IL2 secretion. The levels of other T_H 1 cytokines were also enhanced or restored upon administration of anti-PD-L1. In addition, we show that the suppression of IL27 signaling by IL6-type cytokine pre-stimulation-mimicking a situation occurring, for example, in IL6-secreting tumors or in tumor inflammation-induced cachexia-can be antagonized by antibodies against IL6-type cytokines or their receptors. Therapeutically, the antitumor effects of IL27 (mediated, e.g., by increased antigen presentation) might thus be increased by combining IL27 with blocking antibodies against PD-L1 or/and IL6-type cytokines.

Dual Roles of IL-27 in Cancer Biology and Immunotherapy

IL-27 is a pleiotropic two-chain cytokine, composed of EBI3 and IL-27p28 subunits, which is structurally related to both IL-12 and IL-6 cytokine families. IL-27 acts through a heterodimer receptor consisting of IL-27Rα (WSX1) and gp130 chains, which mediate signaling predominantly through STAT1 and STAT3. IL-27 was initially reported as an immune-enhancing cytokine that supports CD4+ T cell proliferation, T helper (Th)1 cell differentiation, and IFN-γ production, acting in concert with IL-12. However, subsequent studies demonstrated that IL-27 displays complex immune-regulatory functions, which may result in either proinflammatory or anti-inflammatory effects in relationship to the biological context and experimental models considered. Several pieces of evidence, obtained in preclinical tumor models, indicated that IL-27 has a potent antitumor activity, related not only to the induction of tumor-specific Th1 and cytotoxic T lymphocyte (CTL) responses but also to direct inhibitory effects on tumor cell proliferation, survival, invasiveness, and angiogenic potential. Nonetheless, given its immune-regulatory functions, the effects of IL-27 on cancer may be dual and protumor effects may also occur. Here, we will summarize IL-27 biological activities and its functional overlaps with the IFNs and discuss its dual role in tumors in the light of potential applications to cancer immunotherapy.

High Interleukin 27 Production is Associated with Early Clinical Stage and Localized Disease in Patients with Melanoma

BACKGROUND

The immune response in patients with melanoma is an important focus of research due to the tumor's resistance and immunotherapy possibilities. IL-27 is one of the cytokines with antitumor properties. The role of IL-27 in the pathogenesis of melanoma is still unclear. The aim of this study was to examine the association between serum IL-27 levels and the clinical parameters of melanoma patients.

METHODS

The IL-27 concentration was determined by com mercial ELISA in serum samples from melanoma patients (n=72) and healthy control subjects (n=44). Patients were classified according to AJCC clinical stage, TNM stage, the length of progression-free interval (PFI) and the extent of the disease (localized or widespread).

RESULTS

Average IL-27 values were increased in patients with early stages of melanoma compared to patients with terminal stages and control values. The highest IL-27 concentration was found in stage IIa. Patients in stages III and IV had significantly lower values of IL-27 compared to control. Patients with localized melanoma and shorter PFI had insignificantly increased IL-27 levels compared to patients with widespread disease and longer PFI. Patients with metastatic disease and stage TNM4 had significantly lower average IL-27 values compared to control. Patients with high production of IL-27 (>1000 pg/mL) were most numerous in IIa AJCC stage, with initial tumor size TNM2 and in the group of patients with localized disease.

CONCLUSIONS

High levels of IL-27 in patients with melanoma are associated with the initial stages and lo calized disease.

Regulatory circuits of T cell function in cancer

Recent progress in cancer immunotherapy emphasizes the importance of understanding immune-regulatory pathways in tumours. Dysfunction of antitumour T cells may be due to mechanisms that are evolutionarily conserved or acquired by somatic mutations. The dysfunctional state of T cells has been termed 'exhaustion', on the basis of similarities to dysfunctional T cells in chronic infections. However, despite shared properties, recent studies have identified marked differences between T cell dysfunction in cancer and chronic infection. In this Review, we discuss T cell-intrinsic molecular alterations and metabolic communication in the tumour microenvironment. Identification of the underlying molecular drivers of T cell dysfunction is essential for the continued progress of cancer research and therapy.

IL-27 Promotes Proliferation of Human Leukemic Cell Lines Through the MAPK/ERK Signaling Pathway and Suppresses Sensitivity to Chemotherapeutic Drugs

IL-27 is a pleiotropic cytokine of the IL-6/IL-12 family with diverse biological functions. Previous in vivo studies have suggested the antitumor activities of IL-27 in animal models, whereas clinical observations indicate the link of IL-27 in tumor progression. IL-27 has recently been shown to cause inhibition of proliferation on primary leukemic cells from pediatric patients, but information on its role in human leukemic cell lines is limited. In the present study, we investigated the ability of IL-27 to regulate cell growth and survival of various human leukemic cell lines. Our results showed that in human leukemic cell lines coexpressing both IL-27R chains, IL-27Rα and gp130, IL-27 did not inhibit cell growth, but caused dose-dependent proliferation of the acute myeloid leukemic cell line, OCI-AML5, and the erythroleukemic cell lines, TF-1, UT-7, and UT-7/EPO. Consistent with this, IL-27 promoted cell survival and reduced TNF-α-induced apoptosis of the leukemic cell lines. IL-27 also decreased the responsiveness of the leukemic cells to chemotherapeutic drugs, cytarabine and daunorubicin. We observed that IL-27 induced the activation of STAT1/3 and ERK1/2 in the leukemic cells. Growth stimulation by IL-27 was suppressed by the specific MEK inhibitor, U0126, indicating that IL-27-induced cell proliferation is mainly mediated through the activation of the MAPK/ERK signaling pathway. The present study is the first demonstration of the proliferative and antichemotherapeutic properties of IL-27 in human leukemic cell lines, suggesting that IL-27 can play an unfavorable role in tumor growth and can be an important determinant in the chemoresponsiveness of certain subtypes of human leukemia.

The Yin and Yang aspects of IL-27 in induction of cancer-specific T-cell responses and immunotherapy

Accumulating evidences from animal studies have indicated that both endogenous and exogenous IL-27, an IL-12 family of cytokine, can increase antitumor T-cell activities and inhibit tumor growth. IL-27 can modulate Treg responses, and program effector T cells into a unique T-effector stem cell (TSEC) phenotype, which enhances T-cell survival in the tumor microenvironment. However, animal studies also suggest that IL-27 induces molecular pathways such as IL-10, PD-L1 and CD39, which may downregulate tumor-specific T-cell responses. In this review paper, we will discuss the Yin and Yang aspects of IL-27 in the induction of tumor-specific T-cell responses, and the potential impacts of these functions of IL-27 in the design of cancer immunotherapy.

Potential clinical application of interleukin-27 as an antitumor agent

Cancer immunotherapies such as sipuleucel-T and ipilimumab are promising new treatments that harness the power of the immune system to fight cancer and achieve long-lasting remission. Interleukin (IL)-27, a member of the IL-12 heterodimeric cytokine family, has pleiotropic functions in the regulation of immune responses with both pro-inflammatory and anti-inflammatory properties. Evidence obtained using a variety of preclinical mouse models indicates that IL-27 possesses potent antitumor activity against various types of tumors through multiple mechanisms without apparent adverse effects. These mechanisms include those mediated not only by CD8⁺ T cells, natural killer cells and macrophages, but also by antibody-dependent cell-mediated cytotoxicity, antiangiogenesis, direct antiproliferative effects, inhibition of expression of cyclooxygenase-2 and prostaglandin E₂, and suppression of epithelial–mesenchymal transition, depending on the characteristics of individual tumors. However, the endogenous role of IL-27 subunits and one of its receptor subunits, WSX-1, in the susceptibility to tumor development after transplantation of tumor cell lines or endogenously arising tumors seems to be more complicated. IL-27 functions as a double-edged sword: IL-27 increases IL-10 production and the expression of programmed death ligand 1 and T-cell immunoglobulin and mucin domain-3, and promotes the generation of regulatory T cells, and IL-27 receptor α singling enhances transformation; IL-27 may augment protumor effects as well. Here, we review both facets of IL-27, antitumor effects and protumor effects, and discuss the potential clinical application of IL-27 as an antitumor agent.

Characterization of the Microenvironment in Positive and Negative Sentinel Lymph Nodes from Melanoma Patients

Melanomas are aggressive skin tumors characterized by high metastatic potential. Our previous results indicate that Natural Killer (NK) cells may control growth of melanoma. The main defect of blood NK cells was a decreased expression of activating NCR1/NKp46 receptor and a positive correlation of NKp46 expression with disease outcome in stage IV melanoma patients was found. In addition, in stage III melanoma patients, we identified a new subset of mature NK cells in macro-metastatic Lymph nodes (LN). In the present studies, we evaluated the numbers of NK cells infiltrating primary cutaneous melanoma and analyzed immune cell subsets in a series of sentinel lymph nodes (SLN). First, we show that NKp46+ NK cells infiltrate primary cutaneous melanoma. Their numbers were related to age of patients and not to Breslow thickness. Then, a series of patients with tumor-negative or -positive sentinel lymph nodes matched for Breslow thickness of the cutaneous melanoma was constituted. We investigated the distribution of macrophages (CD68), endothelial cells, NK cells, granzyme B positive (GrzB+) cells and CD8+ T cells in the SLN. Negative SLN (SLN-) were characterized by frequent adipose involution and follicular hyperplasia compared to positive SLN (SLN+). High densities of macrophages and endothelial cells (CD34), prominent in SLN+, infiltrate SLN and may reflect a tumor favorable microenvironment. Few but similar numbers of NK and GrzB+ cells were found in SLN- and SLN+: NK cells and GrzB+ cells were not correlated. Numerous CD8+ T cells infiltrated SLN with a trend for higher numbers in SLN-. Moreover, CD8+ T cells and GrzB+ cells correlated in SLN- not in SLN+. We also observed that the numbers of CD8+ T cells negatively correlated with endothelial cells in SLN-. The numbers of NK, GrzB+ or CD8+ T cells had no significant impact on overall survival. However, we found that the 5 year-relapse rate was higher in SLN with higher numbers of NK cells.

A soluble form of IL-27Rα is a natural IL-27 antagonist

IL-27 is a cytokine of the IL-12 family that plays a key role in the regulation of inflammatory and T cell responses. Its receptor is composed of IL-27Rα and gp130 and activates the STAT pathway. We show in this study, using an ELISA that we developed, that a naturally occurring soluble form of IL-27Rα (sIL-27Rα) is produced by human activated CD4(+) and CD8(+) T cells, B cells, myeloid cells, and various cell lines. sIL-27Rα is present at a mean concentration of 10,344 ± 1,274 pg/ml in the sera from healthy individuals. Biochemical studies showed that sIL-27Rα is released as two N-glycosylated variants of ∼ 90 and ∼ 70 kDa. In IL-27Rα-transfected COS7 cells, primary cells, and cell lines, production of sIL-27Rα is inhibited by the metalloprotease inhibitors GM6001 and TAPI-0. Importantly, natural sIL-27Rα binds rIL-27, inhibits IL-27 binding to its cell surface receptor, and is a potent inhibitor of IL-27 signaling, as shown by its ability to specifically block IL-27-mediated STAT activation, at low molar excess over IL-27. Also, we found that serum levels of sIL-27Rα were elevated in patients with Crohn's disease, a Th1-mediated disease. These findings suggest that sIL-27Rα may play important immunoregulatory functions under normal and pathological conditions.