Flow cytometry detection of CD molecules in human peripheral blood, direct-labeled primary antibody recommendations for clones and fluorophore combinations.

Channel combinations should take compensation into account: the proportion of CD25-positive cells is not high, so placing it in APC is usually relatively stable, and APC compensation with PE/FITC is relatively manageable; if CD25 is placed in PE, it may be affected by debris or nonspecific staining. FcR blocking and viability dyes are very important, especially since peripheral blood mononuclear cells are prone to nonspecific adsorption by monocytes/macrophages. When the isotype control budget is tight, FMO controls can be used for gating CD4 and CD8, while an isotype control should be retained for CD25; do not omit all of them.

Do not simply follow the instructions for use regarding the amount; it is recommended to perform antibody titration first: add 0.25, 0.5, 1, or 2.5 μL/test per 1×10^6 PBMC, and determine the optimal amount by staining index or signal-to-noise ratio. The sensitivity of CytoFLEX is not low; for initial use, a small pack of 5 μL/test can be used first; if the cell number is fixed, adding 5 μL to a 1×10^6/tube system is very common. For directly labeled antibodies, avoid repeated freeze-thaw cycles, and aliquot and store protected from light upon arrival. The isotype control must be of the same host species, same isotype, same fluorophore, and same concentration as the antibody; otherwise, it cannot serve as a reliable basis for gating.

For spot supply, you can inquire with Shanghai distributors such as Dakewe, UniNova, Baisai, and Aojing. BioLegend, BD, and eBioscience/Thermo have complete CD antibody product lines. With a budget under 3000, it is recommended to buy three 25 test small packs, and the isotype control can be configured separately; if the usage is large, then consider 100 test. Before placing an order, have the sales representative confirm the clone number, fluorescence, arrival time, and cold chain conditions; do not rely only on the webpage's in-stock status. Some domestic brands such as Sizhengbo and Dakewe's own antibodies are lower in price, but they must be tested on the CytoFLEX to avoid loss of low-expression markers.

Common clones for CD4, CD8, and CD25: CD4 can use OKT4 or SK3, CD8 can use RPA-T8 or SK1, and CD25 commonly uses BC96 or 4E3. The FITC/PE/APC channels on the CytoFLEX are relatively well established. It is recommended to place weakly expressed CD25 in APC or PE, and CD4 and CD8 in FITC and APC/PE. For example, CD4 FITC, CD8 PE, CD25 APC, or CD4 PE, CD8 FITC, CD25 APC. First confirm the instrument's filter configuration to avoid excessive PE/APC compensation affecting the resolution of weak CD25-positive populations.

When you receive the antibody, first check the COA to verify the clone number, fluorescent label, isotype, and recommended storage solution. It is best for the three directly conjugated antibodies to come from the same supplier or the same fluorescent labeling system, making compensation setup easier. If using different brands, it is recommended to first run single-stain tubes to adjust compensation, then run fully stained tubes. The CytoFLEX has automatic compensation, but manual review is still necessary. Do not sacrifice fluorescence brightness and lot-to-lot stability just because of a low budget. For key markers such as CD25, it is recommended to use mainstream brands, while domestic validated options can be considered for routine markers.