The microtiter plate provided in this human IL-2 sRα ELISA kit has been pre-coated with a monoclonal antibody specific to IL-2 sRα. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated polyclonal antibody preparation specific for IL-2 sRα and incubated. IL-2 sRα if present, will bind and become immobilized by the antibody pre-coated on the wells and then become “sandwiched” by biotin conjugate. The microtiter plate wells for this human IL-2 sRα ELISA kit are thoroughly washed to remove unbound IL-2 sRα and other components of the sample. In order to quantitatively determine the amount of IL-2sRα present in the sample, Avidin conjugated to Horseradish Peroxidase (HRP) is added to each microplate well and incubated. Avidin is a tetramer containing four identical subunits, each having a high affinity-binding site for biotin. The wells are thoroughly washed to remove all unbound HRP-conjugated Avidin and a TMB (3,3'5, 5' tetramethyl-benzidine) substrate solution is added to each well. The enzyme (HRP) and substrate are allowed to react over a short incubation period. Only those wells that contain IL-2 sRα, biotin-conjugated antibody, and enzyme-conjugated Avidin will exhibit a change in colour. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the colour change is measured spectrophotometrically at a wavelength of 450nm ± 2nm.

In order to measure the concentration of IL-2 sRα in the samples this human IL-2 sRα ELISA kit includes two calibration diluents (Calibrator Diluent I for serum/plasma testing and Calibrator Diluent II for cell culture supernatant testing.) According to this human IL-2 sRα ELISA kit system, the provided standard is diluted (2-fold) with the appropriate Calibrator Diluent and assayed at the same time as the samples. This allows the operator to produce a standard curve of Optical Density (O.D) versus IL-2 sRα concentration (pg/mL). The concentration of IL-2 sRα in the samples is then determined by comparing the O.D. of the samples to the standard curve. The minimum detectable quantity of human IL-2 sRα as observed using this human IL-2 sRα ELISA kit by the standard curve generated for both Calibrator Diluent I and Calibrator Diluent II is 10 pg/mL. The two standard deviations above the mean optical density of the 20 replicates of the zero standard were defined as the minimum detectable quantities.

This human IL-2 sRα ELISA kit is to be used for the in vitro quantitative determination of human interleukin-2 soluble receptor alpha (IL-2 sRα) concentrations in serum, plasma, cell culture supernatant, and other biological fluids. This sandwich human IL-2 sRα ELISA kit can detect both natural and recombinant human IL-2 sRα. This kit exhibits no significant cross-reactivity with factors related to or associated with IL-2 sRα such as rhIL-2, rhIL-2 sRα.  No significant cross-reactivity was observed with recombinant human: IL-1α, IL-1β, IL-1 sRI, IL-1 sRII, IL-1ra, IL-3, IL-3 sR α, IL-5, IL-5 sR α, IL-5 sRb, IL-6, IL-6 sR, IL-7, IL-8, IL-9, IL-10, IL-11, IL-12, IL-13 ANG, AR, CNTF, β-ECGR, EGF, EPO, FGF acidic, FGF basic, FGF-4, FGF-5, FGF-6, FGF-7, G-CSF, GM-CSF, sgp 130, GRO α, GROβ, GROγ, HB-EGF, HGF, INF-γ, IGF-I IGF-II, LAP (TGF-β1), LIF, M-CSF, MCP-1, MIP-1α, MIP-1β, β-NGF, OSN, PD-ECGF, PDGF-AA, PDGF-AB, PDGF-BB, PTN, RANTES, SCF, SLPI, TGF- α, TGF-β, TNF- α, TNF-β, sTNF RI, sTNF RII, VEGF. Biological samples from apparently healthy, normal individuals were collected and the average IL-2 sRα concentration measured. Serum samples (n=15) average value: 1265 pg/ml, range: 650-2216 pg/mL whereas plasma samples (n=15) average value: 1127 pg/ml, range: 540-3150 pg/mL. This human IL-2 sRα ELISA kit is intended FOR LABORATORY RESEARCH USE ONLY and is not to be used in diagnostic or therapeutic procedures.

The biological function of IL-2 is obtained by binding to the specific interleukin-2 receptor (IL-2R). The IL-2R consists of three non-covalently linked chains, all of which are type I transmembrane proteins and include the α chain (IL-2Rα, p55), β chain (IL-2Rβ, p75), and γ chain (IL-2Rγ, p65). The α chain is cleaved from the cell surface via nonspecific proteolysis. IL-2Rα and IL-2Rβγ dimers bind to different residues on the IL-2 protein. The IL-2Rα complex displays low affinity and the IL-2Rαβ complex displays intermediate affinity for IL-2 binding. Both IL-2Rα and IL-2Rαβ complexes are unable to transduce a signal. The IL-2Rβγ complex has intermediate affinity for IL-2 binding and can transduce a signal with a relatively high concentration of IL-2. The IL-2Rαβγ trimer is the high-affinity receptor for IL-2 and can transduce a signal successfully.

The IL-2 receptor (IL-2R) was the first interleukin receptor to be described and characterized.It was found to have a high affinity binding site and is expressed by antigen-activated T lymphocytes (T cells). Radiolabeled IL-2 concentrations found to saturate these sites (e.g. 1-100 pM) were identical to those determined to promote T cell proliferation. Subsequently, the three distinct receptor chains, termed alpha (α), beta (β) and gamma (γ) were identified. The high affinity of IL-2 binding is created by a rapid association rate (k = 10e7/M/s) contributed to the alpha chain, and a relatively slow dissociation rate (k' = 10e-4/s) contributed to the beta and gamma chains.