This assay employs a two-site sandwich ELISA to quantitate TNF-α in Human serum, plasma. An antibody specific for TNF-α has been pre-coated onto a microplate. Standards and samples are pipetted into the wells and any TNF-α present is bound by the immobilized antibody. After removing any unbound substances, a biotin-conjugated antibody specific for TNF-α is added to the wells. After washing, Streptavidin conjugated Horseradish Peroxidase (HRP) is added to the wells. Following a wash to remove any unbound avidin-enzyme reagent, a substrate solution is added to the wells and color develops in proportion to the amount of TNF-α bound in the initial step. The color development is stopped and the intensity of the color is measured.

TNFa is synthesized as a 26 kDa, type II transmembrane protein that is 233 amino acids in length. It contains a 30 amino acid (aa) cytoplasmic domain, a 26 aa transmembrane segment, and a 177 aa extracellular region. TNFa is assembled intracellularly to form a transmembrane, non-covalently-linked homotrimeric protein. The 157 aa residue soluble form of TNFa (sTNF-α is released from the C-terminus of the transmembrane protein through the activity of TNFa-converting enzyme (TACE), a membrane-bound disintegrin metalloproteinase. Rat cells known to express TNF-αinclude B cells, colonic columnar epithelial cells, NK and CD3 CD56 hepatic natural T cells, macrophages, monocytes and monocyte-derived dendritic cells, CD4 and CD8 T cells, mast cells, neutrophils, keratinocytes, plasma cells, and adipocytes.

This assay has high sensitivity and excellent specificity for detection of Human TNF-α. No significant cross-reactivity or interference between Human TNF-α and analogues was observed.

Matrices listed below were spiked with certain level of recombinant Human TNF-α and the recovery rates were calculated by comparing the measured value to the expected amount of Human TNF-α in samples.

Intra-assay Precision (Precision within an assay) 

Three samples of known concentration were tested twenty times on one plate to assess intra-assay precision.

Inter-assay Precision (Precision between assays) 

Three samples of known concentration were tested in forty separate assays to assess inter-assay precision.

CV (%) = SD/meanX100

Intra-Assay: CV<8% 

Inter-Assay: CV<12%

The linearity of the kit was assayed by testing samples spiked with appropriate concentration ofHuman TNF-α and their serial dilutions. The results were demonstrated by the percentage of calculated concentration to the expected.

The stability of ELISA kit is determined by the loss rate of activity. The loss rate of this kit is less than 5% within the expiration date under appropriate storage condition. The loss rate was determined by accelerated thermal degradation test. Keep the kit at 37°C for 4 and 7 days, and compare O.D.values of the kit kept at 37°C with that of at recommended temperature. (referring from China Biological Products Standard, which was calculated by the Arrhenius equation. For ELISA kit, 4 days storage at 37°C can be considered as 6 months at 2 - 8°C, which means 7 days at 37°C equaling 12 months at 2 - 8°C).

Serum: Use a serum separator tube (SST) and allow samples to clot for two hours at room temperature or overnight at 2 - 8°C before centrifugation for 15 minutes at 1000 × g. Remove serum and assay immediately or aliquot and store samples at ≤ -20°C. Avoid repeated freeze-thaw cycles. Plasma: Collect plasma using EDTA, or heparin as an anticoagulant. Centrifuge for 15 minutes at 1000 × g at 2 - 8°C within 30 minutes of collection. Assay immediately or aliquot and store samples at ≤ -20°C. Avoid repeated freeze-thaw cycles. Other biological fluids: Centrifuge samples for 20 minutes at 1000 × g. Remove particulates and assay immediately or store samples in aliquot at -20°C or -80°C. Avoid repeated freeze/thaw cycles.