Fluorescence sandwich enzyme-linked immunosorbent assay for detecting human interleukin-2 receptors

Determination of age-related changes in human soluble interleukin 2 receptor in body fluids of normal subjects as a control value against disease states

A highly sensitive enzyme-linked immunosorbent assay (ELISA) system was developed for human soluble interleukin-2 receptor (sIL-2R) with an ELISA-amplification system (ELAST((R))). The sensitivity of the new method was 20-fold higher than that without the amplification. Thus very low concentrations of sIL-2R in urine can be detected. With this method, serum and urine concentrations of sIL-2R were analyzed for healthy Japanese subjects with age 1-67 years. Mean sIL-2R concentrations in both serum and urine of children were significantly higher than those of adults. However, the concentrations of children showed a progressive decline to those of adults by the age of 15 years. There was no difference in the values between males and females. The results provide a control value of sIL-2R against those in disease states such as nephrotic syndrome. Since the trends in serum and urine were found to be similar, urinary sIL-2R measurement may provide sufficient information, without measuring the blood concentration.

The role of cytokines in the acquired immunodeficiency syndrome

HIV replication in vitro is regulated by many factors, including various exogeneous stimuli and proteins encoded by either virus or cellular genomes. During the asymptomatic period, cells latently or chronically infected with HIV gradually express virus, leading to immunosuppression and opportunistic infection. These conditions would result in the increased secretion of cytokines, especially TNF, from infected and uninfected cells, which can induce HIV and killing of infected cells. A vicious circle is then set in motion in which heterologous microbial infections directly or indirectly activate HIV and the production of cytokines, thereby accelerating lymphocyte depletion and immunodeficiency. AIDS is a disorder of the immune network caused by a unique retrovirus HIV. However, if the whole story described above is true, this disease can also be termed a "cytokine disease". Immunity resembles a "double-edged sword", with aspects not only protective, but also deleterious to the host. Therefore, it is essential to more extensively investigate the mechanism of cytokine regulation of HIV expression in vivo, not only to understand the complex pathophysiology of AIDS, but also to design a therapeutic strategy to halt this deadly disease.

Differences in IL-2 receptor levels between mycosis fungoides and cutaneous type adult T-cell leukemia/lymphoma in the early stages of the disease

Skin lesions in mycosis fungoides (MF) and cutaneous-type adult T-cell leukemia/lymphoma (c-ATL) are sometimes difficult to differentiate. Our previous investigations showed that the alpha-chain of interleukin-2 receptor (IL-2R alpha) secretion is enhanced in both acute and chronic type ATL. This finding suggested increased levels of IL-2R alpha in c-ATL that might differentiate it from MF. In this study, we report several observations on IL-2R alpha levels in MF and c-ATL. 1) Plasma levels of IL-2R alpha determined by enzyme-linked immunosorbent assay were higher in patients with c-ATL (tumor group, 17,571 +/- 5,919 U/ml; non-tumor group, 4,546 +/- 1,788 U/ml) than those of patients with MF (tumor group, 2,352 +/- 861 U/ml; plaque group, 530 +/- 174 U/ml). 2) The percentages of IL-2R alpha-positive cells in skin lesions of c-ATL were 30.5 +/- 13.4% in the non-tumor group and 62.7 +/- 12.0% in the tumor group, which were significantly higher than those of MF, plaque group (12.7 +/- 5.9%), and tumor group (3.4 +/- 2.3%). 3) Further, there was a significant correlation between plasma IL-2R alpha levels and the number of IL-2R alpha-positive cells in skin lesions in patients with c-ATL (r = 0.654, p < 0.0001) and MF (r = 0.537, p < 0.01) on an individual basis; whereas no increased IL-2R alpha levels in peripheral blood mononuclear cells were observed in patients with either MF or c-ATL. 4) Skin lesions of c-ATL had much higher levels of IL-2R alpha genomic RNA than those of MF in their initial stages when measured by DNase/reverse transcription/polymerase chain reaction and liquid hybridization analysis. These findings suggest that increased plasma IL-2R alpha levels in patients with either MF or c-ATL may be linked to cellular IL-2R alpha levels in the skin lesions, and thus reflect the difference between MF and c-ATL.

Japanese patients with chronic fatigue syndrome are negative for known retrovirus infections

Although chronic fatigue syndrome (CFS) is known to be the syndrome that begins with an acute flu-like illness that may be due to the exposure to an infectious agent, there has been no convincing evidence on the causative agents. Recently, human T-lymphotropic virus type II (HTLV-II)-like virus has been reported to be associated with the CFS by using HTLV Western blot analysis and polymerase chain reaction. However, some investigators could not detect HTLV-II by indirect immunofluorescence analysis. Lately, CFS patients have been reported in Japan. We detected all 30 tested patients with CFS were seronegative for HTLV-II, HTLV-I and HIV by specific peptide ELISA and Western blot. Further, PCR analysis was negative for HTLV-II and retrovirus was not detected by coculture method with patients' PBMC. Thus, known human retrovirus infections do not cause a CFS in Japan.

Production of a monoclonal antibody that defines the alpha-subunit of the feline IL-2 receptor

A mAb, termed 9F23, to feline Con A-stimulated PBMC was prepared to characterize feline IL-2R. 9F23 was identified by FACS studies, which showed that the antigen was expressed at a high density on Con A-induced feline T cell blasts while 9F23 binding was not detected on nonactivated PBMC or the Crandell feline kidney cell line CRFK. Chemical crosslinking of 125I-IL-2 to membrane IL-2Rs on Con A-stimulated feline PBMC under the low-affinity condition resulted in detection of a major 65-kDa band. 9F23 specifically immunoprecipitated the IL-2.IL-2R alpha complex in a cell extract; in contrast, neither anti-human IL-2R alpha H48 nor anti-mouse IL-2R alpha 7D4 reacted with the complex. Moreover, immunoprecipitation with 9F23 of the extract from surface-iodinated Con A-stimulated PBMC showed a major 50-55 kDa band. Furthermore, 9F23 had no effect on either IL-2-driven proliferation of the Con A-stimulated PBMC or IL-2 binding. Finally, the expression of feline IL-2R alpha on Con A-stimulated PBMC was up-regulated by addition of exogenous IL-2. Thus, 9F23 defines an epitope different from the IL-2 binding site on the alpha-subunit of feline IL-2R.

Soluble interleukin-6 receptor is released from receptor-bearing cell lines in vitro

Soluble interleukin-6 receptor (sIL-6R) was found to be spontaneously released from human myeloma cell line U266 cells into culture supernatant, and was quantitatively measured with a fluorescence sandwich enzyme-linked immunosorbent assay employing antibodies specific to IL-6R. The supernatant IL-6R was generated only from IL-6R-positive cell lines; myeloma cell lines RPMI8226 and PRMI1788, and myelomonocytic cell lines U937, THP-1, and HL-60. In contrast, it was not released from the IL-6R-negative cells; T cell line Molt-4 and Burkitt lymphoma cell line Raji. SDS-PAGE analysis of the soluble IL-6R from U266 cells suggested a molecular weight of approximately 50-55 kDa, 25-30 kDa smaller than the mature cell surface receptor. These results suggest that the generation of soluble IL-6R may be a maker of myeloma cells and myelomonocytic cells.

Impaired urinary excretion of soluble IL-2 receptors in patients with systemic lupus erythematosus and rheumatoid arthritis

Several previous studies have demonstrated increased in vivo release of soluble interleukin-2 receptors (sIL-2R) in patients with disorders associated with cellular activation. In this study attempting to understand better the role of sIL-2R released in vivo, we investigated the sIL-2R levels in paired serum and urine samples from 25 patients with systemic lupus erythematosus (SLE), 41 patients with rheumatoid arthritis (RA) and 20 healthy subjects. Using an ELISA for sIL-2R, we detected significantly increased urinary sIL-2R levels in normal individuals (868 +/- 114 units/ml) compared to the corresponding serum samples (209 +/- 25, P < 0.001, mean urine/serum sIL-2R ratio: 4.5 +/- 0.6), which suggests that the clearance of sIL-2R from circulation is largely kidney-dependent. The patients with SLE and RA exhibited significantly increased serum sIL-2R levels compared to normals (682 +/- 115 and 734 +/- 101 units/ml, respectively, P < 0.001) and these levels correlated with disease activity. However, urinary excretion of sIL-2R in these patients (SLE: 620 +/- 154 units/ml; RA: 1084 +/- 148 units/ml) was found to be significantly decreased (mean urine/serum sIL-2R ratio in SLE: 0.9 +/- 0.2; in RA: 1.9 +/- 0.2; P < 0.001) compared to normals, possibly contributing to the accumulation of these soluble receptors in the serum of autoimmune patients after their release from cells. Our findings can be attributed either to the binding of the sIL-2R to serum protein(s) or to distinct structural features of serum sIL-2R in SLE and RA patients, interfering with the urinary excretion of these molecules.

Lymphokine-activated killer induction and its regulation by macrophages in malignant pleural effusions

Mononuclear cells (MNC) from pleural effusions and peripheral blood of 18 patients with primary lung cancer with malignant pleural effusion were studied. Pleural and blood MNC generated lymphokine-activated killer (LAK) activity similarly when cultured for 4 days with an optimal concentration of interleukin 2 (IL-2). Highly purified lymphocytes (greater than 98%) and monocyte-macrophages (greater than 90%) were isolated by discontinuous Percoll gradient centrifugation from pleural and blood MNC. Pleural macrophages, as well as blood monocytes, showed significant augmenting effects on in vitro LAK cell induction from pleural and blood lymphocytes by IL-2. During daily intrapleural administration of IL-2, significant induction of LAK activity in vivo was observed after 3 days, but then this LAK activity in pleural MNC decreased almost to zero by day 15. Daily injections of IL-2 resulted in reduction in the up-regulation of LAK induction by pleural macrophages and also in increases in the levels of soluble IL-2 receptors in pleural effusions. These findings indicate that in vivo LAK induction of lymphocytes in malignant effusions by IL-2 may be regulated by macrophages in the effusions.

A fluorescence sandwich ELISA for detecting soluble and cell-associated human interleukin-2

A fluorescence sandwich ELISA was developed for the quantitation of human interleukin-2 (IL-2) using a combination of two anti-human IL-2 antibodies, L61 and biotinylated anti-IL-2 rabbit IgG. The minimum level of IL-2 detectable by this ELISA was 0.3 pg/ml, indicating that this method is about 100 times more sensitive than the usual colorimetric human IL-2 ELISA. The ELISA specifically detected human IL-2 in cell culture supernatants and serum, and also in extracts from mitogen-stimulated peripheral blood mononuclear cells. All of the IL-2 species detected in the supernatants, sera and cell lysates were shown to have a molecular weight of 15,000, as estimated by size exclusion high performance liquid chromatography.

Utilization of two improved enzyme immunoassays based on avidin-biotin interaction for the detection of Salmonella

Based on a strong interaction between avidin and biotin, two enzyme immunoassays have been modified and tested for the detection of Salmonella typhimurium in foodstuffs. In both assays, the antigen containing sample was first reacted with antibody to Salmonella which was precoated on a polystyrene microtiter plate. The bound antigen was then allowed to react with an appropriate amount of biotinylated antibody. In the first procedure, the presence of Salmonella was quantified by using peroxidase-labeled avidin. In the latter, avidin acted as a bridge between the biotinylated antibody and the biotinylated peroxidase. Samples containing 10(3) and 10(4) cells/ml of the Salmonella virulent strain, respectively, were detectable by these two methods. The results thus compared favorably with the detection limit of the standard ELISA (10(5) cells/ml). The superiority of the modified ELISA's utilizing biotin/avidin interactions was also demonstrated for the detection of Salmonella in artificially contaminated food samples inoculated with only 2-5 Salmonella cells followed by two incubation steps. No significant interference of E. coli (up to 5 x 10(6) cells/ml) was observed in the quantification of Salmonella cells.