Identification of a soluble IL-2 receptor beta-chain from human lymphoid cell line cells

A clone was isolated from the human lymphoid cell line YT that displayed IL-2R beta, and was found to express much higher levels of IL-2R beta than the original cells. Combining cell surface iodination, affinity labeling of the released soluble protein, and fluorescence sandwich-ELISA for both IL-2 and IL-2.(soluble)(s)IL-2R beta reactants revealed the presence of IL-2-binding protein in the culture supernatant as soluble forms of IL-2R beta. By using the fluorescence sandwich-ELISA elevated levels of sIL-2R beta were measured in culture supernatants of human T cell leukemia virus I positive T cell lines. In addition to this constitutive production of sIL-2R beta, normal PBMC could release low levels of IL-2R beta by stimulation with PHA. In contrast, this was not found in certain human T cell leukemia virus I negative T cell, B cell and macrophage lines. Immunoprecipitation of the soluble protein with IL-2R beta-specific mAb characterized it as an apparent 50- to 55-kDa molecule that is distinct from the 45-kDa soluble IL-2R alpha. Moreover, 10 to 15% of the total cell surface molecules were released into culture supernatants. These results suggest that the released IL-2R beta might serve as an immunoregulatory function in IL-2 dependent both normal and abnormal immune responses.     

Correlation between beta 2-microglobulin and soluble interleukin-2 receptor levels in plasma of individuals living in a malarial endemic region

beta 2-Microglobulin (beta 2m) levels were related to the expected immunoprotection in 81 individuals living in a malarial mesoendemic area near Bobo-Dioulasso (Burkina Faso), who were longitudinally followed. Soluble interleukin-2 receptor (sIL-2R) levels were positively correlated to those of beta 2m (r = 0.44; n = 237; P less than 0.001). This suggests that most of the beta 2m could have originated from activated T and B cell membrane turnover. In our study, both beta 2m and sIL-2R were inversely related to IgG antibodies (Ab) against somatic antigen of Plasmodium falciparum (Som-Ag). Therefore, these molecules at high levels could have a down regulating activity, directly or indirectly, on B cells producing this kind of Ab.     

Biological significance of soluble IL-2 receptor

A NUMBER of receptors for growth factors and differentiation antigens have been found to be secreted or released by cells. Following mononuclear cell (MNC) activation and interleukin-2 receptor (IL-2R) expression, a soluble form of the Alpha;-chain of IL-2R (sIL-2R) is released. The sIL-2R has been shown to be present in the culture supernatants of activated MNCs as well as in normal sera and, in higher amounts, in sera from subjects affected by several diseases including neoplastic, infectious and autoimmune ones, and in sera from transplanted patients suffering allograft rejection. The blood sIL-2R levels depend on the number of producing cells and the number of molecules per cell, so that sIL-2R blood values may represent an index of the number and the functional state of producing cells, both normal and neoplastic. Thus, monitoring of the immune system, mostly T-cells and haematological malignancies might be targets for the measurement of sIL-2R. Since many conditions may influence sIL-2R production, little diagnostic use may result from these measurements. However, since blood sIL-2R levels may correlate with disease progression and/or response to therapy, their measurement may be a useful index of activity and extent of disease. The precise biological role of the soluble form of the IL-2R is still a matter of debate. However, we know that increased sIL-2R levels may be observed in association with several immunological abnormalities and that sIL-2R is able to bind IL-2. It is conceivable then that in these conditions the excess sIL-2R released in vivo by activated lymphoid cells or by neoplastic cells may somehow regulate IL-2-dependent processes. On the other hand, it cannot exclude that sIL-2R is a by-product without biological significance. Finally, it is puzzling that in many conditions in which an increase of blood sIL-2R values has been observed, MNCs display a decreased in vitro capacity to produce sIL-2R. These seemingly contrasting findings are discussed in the light of the data showing that sIL-2R production correlates with IL-2 production.     

Interleukin-6 and interleukin-6 receptor secretion by chronic lymphatic leukaemia and normal B lymphocytes: effect of PMA and PWM

Interleukin-6 (IL-6) and soluble interleukin-6 receptor (sIL-6R) were detected in supernatants of cultures of B chronic lymphatic leukaemia (CLL) lymphocytes. Phorbol-12-myristate 13 acetate (PMA) caused a decrease in the levels of IL-6 in 14 out of 16 cultures and an increase in levels of sIL6R in all 15 cases. The effect of pokeweed mitogen (PWM) was variable and not significant. The levels of IL-6 were below the detection limit (60 pg/ml) in sera of 13 CLL patients whereas sIL-6R was detected (13 ng/ml to 97 ng/ml) in the 13 sera. IL6 was not detected in cultures of unstimulated or stimulated with PMA or PWM normal human B cells. Levels of sIL-6R were minimal in cultures of normal B lymphocytes and were increased in PMA stimulated cultures. The results are consistent with the view that B-CLL cells produce spontaneously IL-6 which could act in an autocrine fashion to cause shedding of surface IL-6R and account for the correlation found between serum levels of sIL-6R and B-CLL lymphocyte numbers. The fall in levels of IL-6 in PMA stimulated CLL cultures might express masking or degradation of IL-6 after combination with the receptor.     

Interleukin-2 receptor positive cells and circulating soluble interleukin-2 receptors in patients with solid tumors are not correlated

Activated lymphocytes can release a soluble form of IL-2 receptor (sIL-2R), which retains the capacity to bind IL-2. Abnormally high values of sIL-2R have been observed in patients with advanced solid tumors. In an attempt to further understand the biological significance of sIL-2R in solid tumors, this study investigated the relation between sIL-2R and Tac-positive cells. sIL-2R serum levels and Tac-positive cells were determined in 18 patients with solid tumors metastatic, 108 non-metastatic. Tumor types were: breast 7; lung 6; colon 2; stomach 1; testis 1; larynx 1. No correlation was found between circulating sIL-2R values and Tac-positive cells, and there was no difference between Tac-positive cell mean number in patients with high and normal sIL-2R levels. These preliminary results suggest that different mechanisms are responsible for sIL-2R release in the blood and IL-2 receptor expression on the immune cell surface.     

Interleukin 6 and 8 levels in plasma and fibroblast cultures in psoriasis

Fibroblasts have been implicated in psoriatic inflammatory processes. The aim of the study was to evaluate soluble interleukin 2 receptor (sIL-2R), interleukin 6 (IL-6), and interleukin 8 (IL-8) plasma levels in psoriatic patients and IL-6 and IL-8 levels in fibroblast culture supernatants. Cytokines levels in plasma and supernatants were measured by ELISA. Plasma sIL-2R, IL-6, and IL-8 levels were higher before the treatment in comparison to healthy controls (P < 0.001) and decreased after treatment. Fibroblasts from healthy controls, psoriatic lesional skin, and noninvolved psoriatic skin, when stimulated with tumor necrosis factor alpha, released considerable amounts of IL-6 and IL-8. No significant difference between healthy controls and psoriatic fibroblasts was observed. Monitoring plasma sIL-2R levels could be employed as a reliable method of psoriasis activity. IL-8 and IL-6 plasma levels seem to reflect psoriasis activity, and treatment response, respectively. Fibroblasts are not a major source of increased IL-6 and IL-8 production in psoriasis.     

The clinical significance of serum soluble interleukin 2 receptor (sIL-2R) concentration in lung cancer

The activated mononuclear cells can release a soluble form of interleukin 2 receptor (sIL-2R) in the blood. Serum sIL-2R level is a sensitive and quantitative marker of circulating peripheral blood mononuclear cell activation. This molecule acts as an antagonist of IL-2-mediated responses. The present study was carried out to analyze the circulating levels of sIL-2R in lung cancer in relation to the histological type of the tumour, clinical stage, response to therapy, time survival for patients. The study included 62 patients (30 SCLC, 32 NSCLC) and 10 healthy subjects as controls. SIL-2R serum levels were measured with a sandwich enzyme immunoassay using commercial kits (ENDOGEN). The mean serum values of sIL-2R were significantly higher in cancer patients than in controls (p=0.01). There was no significant difference in relation to tumour histological type. Within the NSCLC chemotherapy group, sIL-2R mean levels observed at the end of chemotherapy were higher in the progressing patients than in the responding patients. The metastatic patients had higher levels of sIL-2R than those with locally limited disease. In the case of SCLC classified to extensive disease mean levels of sIL-2R were higher than SCLC classified to limited disease. The mean serum values of sIL-2R were significantly higher in weight loss patients than no weight ones (p=0.03). Within NSCLC group there was a correlation between sIL-2R mean levels and the age of patients (p=0.04). In SCLC group there was a correlation between levels of sIL-2R and time survival for patients (p=0.009).     

Soluble IL-2 receptor levels in serum from blood donors seropositive for HIV

Serum levels of soluble IL-2R (sIL-2R) were measured in blood donors seropositive for HIV. Approximately one-half (53/101) of these seropositive donors exhibited increased serum sIL-2R levels compared with seronegative controls (n = 65). Further, a significant inverse correlation was observed between serum sIL-2R levels and CD4 cell levels in seropositive study participants. These findings suggest that increased serum sIL-2R levels in HIV infection may be linked to CD4 cell loss, and thus reflective of the stage of HIV-induced disease.     

A soluble form of IL-13 receptor alpha 1 promotes IgG2a and IgG2b production by murine germinal center B cells.

A functional IL-13R involves at least two cell surface proteins, the IL-13R alpha 1 and IL-4R alpha. Using a soluble form of the murine IL-13R alpha 1 (sIL-13R), we reveal several novel features of this system. The sIL-13R promotes proliferation and augmentation of Ag-specific IgM, IgG2a, and IgG2b production by murine germinal center (GC) B cells in vitro. These effects were enhanced by CD40 signaling and were not inhibited by an anti-IL4R alpha mAb, a result suggesting other ligands. In GC cell cultures, sIL-13R also promoted IL-6 production, and interestingly, sIL-13R-induced IgG2a and IgG2b augmentation was absent in GC cells isolated from IL-6-deficient mice. Furthermore, the effects of the sIL-13R molecule were inhibited in the presence of an anti-IL-13 mAb, and preincubation of GC cells with IL-13 enhanced the sIL-13R-mediated effects. When sIL-13R was injected into mice, it served as an adjuvant-promoting production to varying degrees of IgM and IgG isotypes. We thus propose that IL-13R alpha 1 is a molecule involved in B cell differentiation, using a mechanism that may involve regulation of IL-6-responsive elements. Taken together, our data reveal previously unknown activities as well as suggest that the ligand for the sIL-13R might be a component of the IL-13R complex or a counterstructure yet to be defined.     

Soluble IL-2-receptor and CD8 in the serum and the periparasitic granuloma of patients with alveolar echinococcosis.

Cellular immunity plays a key role in the defence against the larva of the cestode Echinococcus multilocularis. This larva is responsible for alveolar echinococcosis (AE) of the liver, a rare parasitic disease which occurs in endemic areas including European alpine countries, Alaska, the USSR, Western China and Northern Japan. We have shown a marked decrease of the CD8+ T-cell population in the blood and we have described an infiltrate composed mainly of activated CD8+ T-cells in the liver lesions of most patients with AE. In this study, we assessed the serum level of soluble IL-2-receptor (sIL-2R) and CD8 (sCD8) in 37 patients (23 men, 14 women, mean age 59.5 yrs) with a histologically proven AE. The results, obtained using sandwich ELISA, were compared to those of healthy controls and correlated to parameters evaluating the severity of the disease. The mean serum levels of sIL-2R were significantly higher in AE patients than in controls. There was a significant correlation between sIL-2R levels and both the volume of parasitic lesions and a calculated index of severity of the disease. The mean serum levels of sCD8 did not differ significantly from the values obtained in controls. These results indicate that the infiltration of the liver by CD8+ T-lymphocytes is not associated with an increased release of sCD8 into the serum. The circulating levels of sIL-2R appear to reflect the extent as well as the severity of the disease. Immunostaining of the cells of the periparasitic granuloma suggests that the cell origin of the sIL-2R could be macrophages rather than T-lymphocytes.     

Effect of soluble interleukin-6 receptor alpha and interleukin-6 secreted by polymorphonuclear leukocytes on tumor necrosis factor-alpha expression and its production by peripheral blood mononuclear cells

BACKGROUND: It has recently been shown that soluble interleukin-6 receptor (sIL-6R) alone or complexed with interleukin (IL)-6, besides their regulatory role in a wide variety of both normal and abnormal biologic reactions mediated by IL-6, could be an effective stimulator of the cell function. AIMS: The key question of the present study is whether the sIL-6Ralpha or sIL-6R with IL-6 released by polymorphonuclear leukocytes (PMN) can influence cytokine secretion such as tumor necrosis factor-alpha (TNF-alpha) by peripheral blood mononuclear cells (PBMC), which together with PMN develop the inflammatory and immune response of a host. METHODS: Cells were isolated from heparinized whole blood of healthy persons. The PMN were cultured for 1 h at 37 degrees C in 5% CO(2). After incubation, the culture supernatant of PMN was removed and was added to PBMC. The PBMC were cultured for 1 h at 37 degrees C in the same conditions. In the culture supernatants and lysates of PMN, we examined the concentrations of sIL-6R by enzyme-linked immunosorbent assay (ELISA). TNF-alpha was measured at both protein and mRNA levels. Protein levels were determined by ELISA. To examine TNF-alpha mRNA expression, we isolated mRNA from PBMC after culture, using TRIZOL Reagent. The quantity of mRNA TNF-alpha was determined by the Quantikine mRNA assay. RESULTS AND CONCLUSION: The results obtained revealed that sIL-6R with IL-6 secreted by PMN may play a regulatory role in the immune response by modulating the TNF-alpha expression and its production by PBMC. This may have a significant influence on an early phase of the inflammation and other reactions mediated by TNF-alpha.     

Serum soluble interleukin-2 (IL-2) receptor levels in women with breast carcinoma and its correlation with IL-2 receptor expression on blood lymphocytes and lymphocytic infiltration within the tumour

Summary This study describes serum levels of soluble interleukin-2 receptor (sIL-2R) in 13 healthy women, 10 women with breast dysplasia and 37 patients with breast carcinoma. A difference was found between sIL-2R levels in normal women and cancer patients. sIL-2R increased with the advance in stage of cancer but the extent of increase fell from stage III to stage IV as compared to the change from stage II to stage III. Of the 15 patients who were followed after surgery and/or therapy, 10 (67%) showed a fall in the serum sIL-2R levels. A negative correlation was found between sIL-2R levels and lymphocytic infiltration only within the malignant tissue. These findings probably indicate that sIL-2R exerts an immunomodulatory effect on blood lymphocytes by preventing their infiltration into the tumour tissue. To our knowledge, this is the first report of its kind in immunology of breast carcinoma.     

Quantitative analysis of serum IL-6 and its correlation with increased levels of serum IL-2R in HIV-induced diseases

We have devised a luminescence sandwich ELISA for the quantification of IL-6 in both sera and cell culture supernatants, which had a detection limit of 100 fg/ml of test sample. By using the luminescence sandwich-ELISA, low but measurable levels of IL-6 (9.5 pg/ml on average) were found in the sera from normal individuals. The serum levels of IL-6 were elevated in HIV-seropositive asymptomatic carriers (55.5 pg/ml on average), and the IL-6 levels were correlated with the degree of HIV-induced disease progression (AIDS-related complex 106.8 pg/ml on average and (AIDS 283 pg/ml). IL-6 immunoreactivity in the sera of AIDS patients eluted at a 25,000 m.w. major peak, which was biologically active and heat-stable, and a 500,000 m.w. minor peak in size-exclusion HPLC. Interestingly, a significant correlation was observed between the serum IL-6 levels and soluble IL-2R levels. In vitro, HIV infection of PHA-activated PBMC led to enhanced release of IL-6 into the culture supernatants. Moreover, soluble IL-2R release was markedly increased by adding exogenous IL-6, whereas it was decreased by adding the neutralizing anti-IL-6 mAb to the cultures. These results demonstrate that increased IL-6 levels are significantly associated with sIL-2R levels, and suggest a cause of the increased levels of this receptor in patients with HIV infection. Furthermore, both serum IL-6 and serum IL-2R levels in HIV infection reflect the stage of the HIV-induced disease.     

Highly concentrated urine-purified Tac peptide fails to inhibit IL-2-dependent cell proliferation in vitro.

Tac peptide, i.e., the p55 chain of the human interleukin-2 receptor (IL-2R) complex, is detectable as a soluble from (sIL-2R) in normal sera and, at increased levels, in patients with different diseases. Since several immunological abnormalities are observed in most conditions associated with an increase in sIL-2R levels, a down-regulatory effect on IL-2-dependent functions has been postulated as a consequence of binding and functional block of IL-2 by the excess of sIL-2R. To test this hypothesis, we purified sIL-2R from the urine of a patient with hairy cell leukemia and investigated the possible inhibitory effect of this peptide on the in vitro IL-2-induced cell proliferation. The urine-purified molecule was detectable by the specific immunoassay utilized to measure the serum Tac peptide and was constructed by a single polypeptide of about 50 kDa which was able to bind IL-2. Experiments performed with the IL-2-dependent murine CTLL-2 cell line and with PHA-stimulated human peripheral blood mononuclear cells showed that the purified sIL-2R at concentrations up to about 300 nM was unable to block IL-2-dependent cell proliferation. According to these data, which can be explained by the low affinity for IL-2 of the p55 IL-2R chain, it seems unlikely that in vivo the soluble Tac peptide can exert a down regulatory effect on IL-2-induced phenomena through a functional block of IL-2.     

Detection of soluble interleukin-2 receptor and soluble intercellular adhesion molecule-1 in the effusion of otitis media with effusion

We measured sIL-2R, TNF-alpha and sICAM-1 in the sera and middle ear effusions (MEEs) of patients with otitis media with effusion (OME). Although there was no signmcant difference between the sIL-2R levels of the serous and mucoid MEEs, they were significantly higher than serum sIL-2R levels of OME patients and healthy controls. TNF-alpha levels of the mucoid MEEs were significantly higher than those of the serous type. However, TNF-alpha was rarely detected in the sera of OME patients or healthy controls. We observed significant differences between the serous and mucoid MEEs with respect to their sICAM-1 levels, which were also higher than serum slCAM-1 levels of OME patients and healthy controls. Our findings suggested that IL-2, TNF-alpha and ICAM-1 could be significantly involved in the pathogenesis of OME through the cytokine network.     

Use of an antibody against the soluble interleukin 2 receptor alpha subunit can modulate the stability and biodistribution of interleukin-2

The authors have previously reported that the soluble serum form of the alpha subunit of the IL-2 receptor (sIL-2Ralpha), whose natural half-life is approximately 40 min, survived much longer in the circulation when bound by a specific antibody. In the present study, the authors evaluated the extent to which sIL-2Ralpha protected IL-2 in freshly collected serum using biochemical analyses, and a functional CTLL-2 assay. In particular, sIL-2Ralpha protected IL-2 from forming complexes with alpha(2)-macroglobulin and from inactivation in vitro. In addition, the authors demonstrated that the anti-IL-2Ralpha monoclonal antibody 7G7/B6, which does not inhibit the binding of IL-2 to its binding site on sIL-2Ralpha, protected IL-2 from degradation and inactivation in vivo in the presence of sIL-2Ralpha. Both(125)I-labelled and unlabelled IL-2 were injected into mice preinjected with humanized anti-Tac (hTac) or 7G7/B6 and sIL-2Ralpha, or sIL-2Ralpha alone. Using size-exclusion HPLC, ELISA, and CTLL-2 cell proliferation assays, we observed that the presence of 7G7/B6 led to formation of complexes with sIL-2Ralpha and increased the serum levels of IL-2 more than 3- to 40-fold those of groups receiving IL-2 alone, sIL-2Ralpha, or hTac. Taken as a whole, these results suggest that the complex of 7G7/B6 and sIL-2Ralpha not only prolongs the survival of IL-2 in vivo, but also maintains the bioactivity of IL-2. The use of antibodies against endogenous soluble receptors could increase the in vivo survival of cytokines, protect their bioactivity and thereby facilitate their clinical use in the treatment of various malignancies and AIDS.     

Human soluble IL-6 receptor: its detection and enhanced release by HIV infection.

By using a fluorescence sandwich ELISA for the quantification of soluble human IL-6R, normal human PBMC were found to be induced to release IL-6R into culture supernatant by stimulation with PHA. Furthermore, certain promonocyte cell lines and human T-cell leukemia virus I (HTLV-I)-positive cell lines produced sIL-6R into culture supernatants constitutively. However, this was not found with HTLV-I negative T cell lines and Burkitt's B cell line. In addition, generation of supernatant IL-6R of the promonocyte cell line was significantly increased 27-fold after PMA treatment and sevenfold after infection with HIV. The released IL-6R molecules were characterized as an apparent m.w. of 50 to 55 kDa by both size-exclusion HPLC and immunoprecipitation of the soluble protein with IL-6R-specific mAb followed by SDS-PAGE analysis. Furthermore, increased levels of serum IL-6R were detected in blood donors seropositive for HIV. Moreover, the released IL-6R could bind efficiently to purified rIL-6 on solid phase and suppressed the proliferative responses of PBMC. These results suggest that the release of soluble IL-6R might be linked to regulatory functions of immune responses induced by IL-6 stimulation during normal and human retrovirus-infected cell growth and differentiation.     

High serum levels of soluble interleukin-2 receptor in acute myeloid leukemia: Correlation with poor prognosis and CD4 expression on blast cells

Backgorund: Although increased serum levels of soluble interleukin-2 receptor (sIL-2R) and their clinical importance are well known in mature type lymphoproliferative disorders (LD), little data is available about such information in acute type hematological malignancies. Methods: We examined the serum levels of sIL-2R in 57 adult patients with acute type leukemias: 32 with acute myeloid leukemia (AML), 14 acute lymphoblastic leukemia (ALL) and 11 chronic myelocytic leukemia in blast crisis (CMLBC), and in 29 adult patients with mature type LD, and assessed their cellular and clinical relevance in acute type leukemias. Results: No significant differences were seen in the sIL-2R levels between acute type leukemias and mature type LD. In AML, serum sIL-2R levels were related to the cell surface CD4 expression on blast cells, and patients with higher levels ≧2000U/ml had a poorer prognosis (lower response to chemotherapy and shorter overall survival). Conclusions: These results suggest that serum sIL-2R level elevates in acute type leukemias like mature type LD, and increased sIL-2R levels in adult AML are correlated with certain biological and clinical characteristics.     

G-CSF therapy and catheter-related Gram-positive sepsis increase serum IL-2 receptor α level and may falsely suggest a relapse in children with soft tissue sarcomas unless serum beta2-microglobulin, lactate dehydrogenase and C-reactive protein levels are determined concomitantly

Many components of oncologic treatment increase serum sIL-2Rα level, which may falsely suggest a relapse. We tried to establish whether granulocyte colony stimulating factor (G-CSF) and central vein catheter (CVC)-related sepsis increase serum sIL-2Rα level to values on relapse of childhood soft tissue sarcomas (STS) and how to distinguish real relapse from a "false" one. Serum sIL-2Rα, B2-M, LDH, CRP and ESR levels and rates of markers' elevated values were determined prospectively in 18 STS children: pre-treatmently (ST1), in complete remission (CR; ST2), in CR during G-CSF therapy (ST3), in CR during CVC-related sepsis (ST4), on relapse (ST5) and after treatment (ST6) and once in 50 healthy pediatric controls. It appeared that pre-treatment serum sIL-2Rα, LDH, CRP and ESR but not B2-M declined significantly with remission (ST2) achievement. At ST5 sIL-2Rα, B2-M, LDH and CRP increased from ST2 to ST1 values. SIL-2Rα levels at ST3 and ST4 rose significantly in all patients from ST2 to ST1 and ST5 values. At ST3 also serum LDH and B2-M increased to values at ST1 and ST5 and exceeded significantly those at ST2 and ST4. At ST4 CRP but not B2-M and LDH, rose significantly in most patients to values at ST1 and ST5. Thus, serum sIL-2Rα monitoring in pediatric STS reflects well response to chemotherapy unless samples are collected during G-CSF therapy or CVC-related sepsis. Determination of serum B2-M, LDH and CRP together with sIL-2Rα may help to distinguish between "real" relapse and "false" sIL-2Rα increase due to G-CSF administration or CVC-related sepsis.     

Dynamic changes in soluble interleukin-2 receptor levels during treatment of Graves' disease. Correlation with disease activity

The activation of T lymphocyte is accompanied by the release of soluble interleukin-2 receptors (sIL-2R) which can be assessed in biological fluids. A prospective study of the dynamic changes in sIL-2R levels was performed in the serum of 10 patients undergoing a medical treatment for Graves' disease. All patients received carbimazole during the study and, when necessary, L-thyroxine to compensate hypothyroidism. sIL-2R levels were measured before (M0) and after the 1st (M1), 3rd (M3) and 6th month (M6) of treatment. The levels of sIL-2R were high at M0 and M1, and decreased significantly between M1 and M3 (p = 0.03). At M0, the levels of sIL-2R were highly correlated with triiodothyronine (T3) levels (p = 0.0003), early [131I] uptake (p = 0.007) and, to a lesser degree, with anti-thyrotropin receptor antibody levels (p = 0.02). At M6, no correlation was found anymore. We conclude that sIL-2R levels are increased in patients with untreated Graves' disease. They are highly correlated with the markers of Graves' disease activity and decrease during medical treatment.