For measuring IL-6 in cell supernatants by ELISA in mice, is there a big difference between domestic and imported kits?

High-sensitivity versions are not necessarily suitable for you. High sensitivity is generally achieved by optimizing the antibody pair and substrate to improve low-end sensitivity, but the upper detection limit is often lower, sometimes only 250-500 pg/mL. For macrophage polarization, especially with LPS stimulation, IL-6 often easily exceeds a thousand, so switching to a high-sensitivity kit would actually require more dilution, and dilution error would outweigh the benefits of high sensitivity. The standard sensitivity version is sufficient. If your main concern is low values, you can choose a regular high-range kit with a lower standard curve lower limit but an upper limit that still reaches 1000-2000, or run a pilot experiment comparing the two versions.

If performed weekly with few samples, domestic options are a practical choice, but it is recommended to perform a one-time cross-validation with imported kits. Take 6-8 cell supernatants covering low, medium, and high concentrations, measure them with domestic and imported kits (R&D, BD, BioLegend, etc.), and examine the correlation coefficient and direction of bias. If the bias is systematic, a laboratory-specific correction factor can be established, and domestic kits can be used long-term to track trends. Another common cause of high replicate well CV is slow pipetting leading to inconsistent color development times; it is recommended to use multichannel pipettes, standardize the pipetting sequence, and use a timer for substrate color development in the dark.

Centrifugation of macrophage supernatant is a basic procedure. It is recommended to centrifuge at 1000×g, 4°C for 5-10 minutes to remove cells and debris, then aliquot the supernatant and freeze it. Avoid repeated freeze-thaw cycles, as IL-6 will be affected. Regarding dilution, it depends on the stimulation intensity: IL-6 in macrophage supernatant stimulated with LPS for 24h may reach several hundred to over a thousand pg/mL, while the upper limit of a standard curve for a typical kit is approximately 1000-2000, so it may exceed the upper limit. It is recommended to first test three dilutions: 2-fold, 5-fold, and 10-fold, to find the appropriate range. When the matrix of the cell supernatant differs from that of the standard diluent, it is best to dilute with the diluent provided with the kit.

Batch-to-batch variability in domestic ELISA kits does indeed exist, but the top few brands (Lianke, Sizhengbo, Xinbosheng, Dayou) are now more consistent than their OEM-labeled counterparts. The poor standard curve linearity and high CV of replicate wells you mentioned are not entirely the kit's fault: insufficient standing time after standard reconstitution, infrequent tip changes during serial dilution, residual plate washing, and uneven incubation temperature can all amplify these issues. It is recommended to purchase three consecutive batches from the same manufacturer, use the same quality control supernatant in three replicate wells for each batch, and examine the inter-batch CV; at the same time, ask the sales representative to provide the COA for that batch and the OD values of a typical standard curve. If two consecutive batches both fail, then consider switching.