Principle of Assay
This enzyme linked immunosorbent assay (ELISA) applies a technique called a quantitative sandwich immunoassay. The microwells on the 8-well strips enclosed in the kit have been precoated with monoclonal antibodies specific to IL-1α, IL-1β, L-6, IL-8, INF-γ, GM-CSF, MCAF, and TNF-α, respectively. Standards or samples are then added to the strips, and the biotinconjugated detection antibody mixture will be added late on. The above cytokines, if present, will bind and become immobilized by the antibody pre-coated on the wells and then be “sandwiched” by biotin conjugate. The microtiter plate wells are thoroughly washed to remove unbound components of the sample. In order to quantitatively determine the amount of cytokine 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 that each has a high affinity-binding site for biotin. The wells are thoroughly washed to remove all unbound HRP-conjugated Avidin. 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 coating antibody and the specific cytokine, biotin-conjugated antibody and enzyme-conjugated Avidin will develop a blue colour. The intensity of colour development is proportional to the concentration of the specific cytokine presented in the each wells. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the colour will change to yellow. The intensity is measured spectrophotometrically at a wavelength of 450nm ± 2 nm.
Samples were tested together with standards diluted with a similar matrix, or one of the Calibrator Diluent provided with the kit. This allows the operator to produce Optical Density (O.D) versus cytokine concentration (pg/mL). The concentration of cytokines in the samples is then determined by comparing the O.D. of the samples to the standards.
