What should I do if the background is always high when measuring mouse liver tissue homogenate with IL-6 ELISA?

We recommend performing spike recovery and matrix parallelism. Add the standard to the standard diluent and the diluted liver homogenate supernatant separately, compare the OD, and calculate the recovery. If the recovery in the liver matrix is markedly low or the background is high, this indicates matrix interference or soluble receptor binding, and it may be necessary to switch brands or use further dilution. We have encountered liver samples in which pre-blocking with 0.1% BSA or extending the blocking time provided some improvement but was unstable, and ultimately resolved the issue by increasing the dilution factor and optimizing centrifugation.

Avoid using detergent-containing RIPA for the homogenate, as NP-40 or SDS will interfere with the coating antibody and cause high background. It is recommended to use neutral PBS or the lysis buffer recommended by the kit, adding only protease inhibitors; do not add unnecessary components such as phosphatase inhibitors or DTT. After homogenization, if conditions permit, measure protein concentration using BCA and normalize the total protein across samples, for example, by diluting to the same protein range before loading, so that both background and signal are easier to control.

Homogenization and centrifugation conditions must be sufficient: We have worked with liver tissue, homogenized in PBS, then centrifuged at 4°C, 12000 g for 15 minutes. When collecting the supernatant, avoid the upper white lipid layer and the lower pellet, and take only the clear middle portion. If centrifugation is insufficient or lipid is aspirated, the background will be significantly higher. You can also increase the number of plate washes; if the instructions say 3 times, I do 5 times, with a 30-second soak each time, which can reduce nonspecific signal. A normal standard curve indicates that the antibodies and color development system are fine, so the problem is more likely on the sample side.

High background in liver tissue homogenate is very common. First perform gradient dilution; do not load 50 ul of the original sample directly. We generally start liver homogenate supernatant at 1:10 and prepare 1:10, 1:20, and 1:50 dilutions to see whether the OD decreases linearly with dilution. If the OD still does not decrease after dilution, it may not be due to high concentration, but rather nonspecific binding or matrix interference. Use the sample diluent provided with the kit for dilution, not pure PBS; PBS sometimes amplifies background.