recoveryELISA - TNFa Neutralization Rate/Infliximab Kit (RTI)

Introduction
Tumour necrosis factor (TNFα) is a signalling substance of the immune system which can cause, among other things, the formation of inflammatory mediators in cells. In inflammatory diseases such as rheumatoid arthritis, there is overproduction of TNFα, which can be inhibited by using therapeutic antibodies.

Infliximab is an chimeric monoclonal antibody which is used as a TNFα inhibitor. Infliximab binds specifically to the TNFα protein and neutralises the biological effect of TNFα.

Infliximab is approved for the treatment of the following diseases: rheumatoid arthritis, psoriatic arthritis, psoriasis, ankylosing spondylitis, Crohn`s disease and ulcerative colitis.

In therapy using Infliximab, contraindications such as hypersensitivity to Infliximab and also serious infections, sepsis, tuberculosis and cases of opportunistic infections have been noted. Weakening of the body`s defence is produced by the immunosuppressive effect of Infliximab. Excessive neutralization of TNFα during treatment with Infliximab increases the risk of developing opportunistic infections.

In view of this, monitoring the treatment antibody levels and degree of neutralization of TNFα would appear useful during therapy using the TNFα inhibitor Infliximab.

In comparison with the tests available on the market, the recoveryELISA TNFα Neutralization Rate/Infliximab (RTI) Kit can be used to simultaneously determine the free TNFα target antigen, the available therapeutic antibody Infliximab and its ability to neutralise TNFα.

Intended use
The recoveryELISA RTI is an in-vitro diagnostic agent for the simultaneous quantitative determination of free TNFα, the TNFα neutralization rate (Infliximab activity) and the available therapeutic antibody Infliximab in human serum samples. It consists of a manual, non-automated kit for the determination of 7 samples.

User community
The test is intended for doctors and specialist personnel in clinical chemical laboratories with experience of conducting immunoassays. The test is intended for research purposes only.

Methodology
The recoveryELISA (Enzyme-Linked Immunosorbent Assay) is an immunological quantitative detection method based on a sandwich ELISA. In comparison to a classic sandwich ELISA, a twodimensional calibration is carried out for recoveryELISA obtaining two analysis results within the same assay. The following calibrations are performed:

1. TNFα levels without and with additional Infliximab against extinction (optical density)
2. Infliximab levels against TNFα recovery

RecoveryELISA is performed in a 96-well microplate. The wells of the microplate are pre-coated with a specific capture antibody against human TNFα that binds free TNFα from the patient sample. There occurs a simultaneous incubation of the TNFα calibrators (with and without the addition of Infliximab) of the samples and of the detection conjugate (peroxidase conjugate of an anti-TNFα antibody). Incubation takes place over 16 to 22 hours at 2 to 8°C. After washing, the colour substrate TMB (tetramethylbenzidine) is added to the wells. After incubation the enzymatic colour reaction is stopped using a sulphuric acid solution. A colour change from blue to yellow occurs that is optically detected. Using a wavelength of 450 nm (reference value 620 nm), the optical density (OD) of the reaction product is measured with a suitable microplate reader.

With the aid of the two calibrations to be performed, an evaluation procedure can be carried out to determine the concentrations of free TNFα and Infliximab in the patient samples using the measured OD values. Determination of the therapeutic antibody is based on the principle that the presence of Infliximab in patient samples leads to a systematic reduction in the recovery of TNFα. The evaluation is performed using non-linear regression (Marquardt-Levenberg algorithm), the Michaelis-Menten model from enzyme kinetics and the Langmuir isotherm from surface binding.