Natalizumab is a humanised IgG4k monoclonal antibody produced in murine myeloma cells. Natalizumab contains human framework regions and the complementarity-determining regions of a murine antibody that binds to a4-integrin. Natalizumab is used to treat multiple sclerosis-MS. It is thought to help by preventing patient’s immune system from attacking the nerves in the brain and spinal cord. Natalizumab is also used to treat a bowel condition called Crohn's disease (CD). BioSim™ Natalizumab ELISA kit has been developed for specific quantification of Natalizumab concentration in human serum or plasma with high sensitivity and reproducibility. Natalizumab ELISA kit is based on the sandwich ELISA principle. Standards and samples (serum or plasma) are added in the microtiter plate coated with the reactant for Natalizumab. After incubation, the wells are washed. The HRP conjugated probe is added and binds to Natalizumab captured by the reactant on the surface of the wells. Following incubation wells are washed and the bound enzymatic activity is detected by addition of TMB chromogen substrate. Finally, the reaction is terminated with an acidic stop solution. The color developed is proportional to the amount of Natalizumab in the sample or standard. Results of samples can be determined directly using the standard curve.