Interleukin-2 (IL-2), also known as T-Cell Growth Factor (TCGF), is a molecule with a molecular weight of 15-18 kDa, characterized by varying glycosylation of its alpha-helical polypeptide chain. Il-2 has essential roles in key functions of the immune system, tolerance and immunity, primarily via its direct effects on T cells. The major sources of IL-2 are activated CD4+ T cells and activated CD8+ T cells.

This assay kit employs the double antibody sandwich enzyme-linked immunosorbent assay (ELISA) technique. Specific anti-human IL-2 antibodies with high affinity are pre-coated onto the enzyme-linked plate. In the wells of the enzyme-linked plate, standards, test samples, and biotinylated detection antibodies are added. After incubation, IL-2 present in the samples binds to the solid-phase antibody and the detection antibody, forming an immune complex. After removing unbound substances, streptavidinhorseradish peroxidase labeled with horseradish peroxidase (HRP) is added. After wash step to remove any unbound substances, 3,3′,5,5′-Tetramethylbenzidine (TMB)substrate is added and color develops in proportion to the amount of IL-2 bound initially. The assay is stopped, and the optical density of the wells is determined using a micro-plate reader at 450nm wavelength (with a reference wavelength of 540nm or 570nm) for quantification.

Recovery
Human IL-2 of different levels was spiked into cell culture medium samples to determine its recovery rate. The recovery rate ranged from 102-104%, with an average recovery rate of 103%.
Sensitivity
The minimum detectable dose (MDD) of Human IL-2 is typically less than 3.24 pg/mL.

The MDD was determined by adding two standard deviations to the mean O.D. value of twenty zero standard replicates and calculating the corresponding concentration.
Linearity
To assess the linearity of the assay, four samples spiked with high concentrations of Human IL-2 were diluted with 1×Reagent Diluent to bring them within the detection range.

Specificity
This assay recognizes natural and recombinant Human IL-2.

The factors listed below were prepared at 50 ng/mL in 1×Reagent Diluent and assayed for cross-reactivity.

Preparations of the following factors prepared at 50 ng/mL in a mid-range Human IL-2 control were assayed for interference. No significant cross-reactivity or interference was observed.