The system exploits the exceptionally high-affinity interaction between biotin, a small 244 Da vitamin, and streptavidin, a tetrameric protein isolated from Streptomyces avidinii. The dissociation constant is approximately 10⁻¹⁵ M, one of the strongest non-covalent interactions known in biology, providing stable binding under diverse assay conditions. Streptavidin is a tetramer capable of binding four biotin groups per molecule, and unlike avidin it lacks the glycoprotein portion, resulting in lower non-specific binding. This multivalency enables signal amplification, as multiple streptavidin-fluorophore molecules can bind each biotinylated primary antibody, enhancing sensitivity for low-abundance porcine antigens.

Applications

Biotinylated anti-pig primary antibodies, used in conjunction with streptavidin conjugates, are validated across multiple immunoassay platforms, with flow cytometry as the primary application. They enable identification of T lymphocytes (anti-CD3ε, clone PPT3), helper T cells (anti-CD4, clone 74-12-4), cytotoxic T cells (anti-CD8α, clone 76-2-11), monocytes and granulocytes (anti-CD172a, clone 74-22-15), and dendritic cell subsets (anti-CD1, clone 76-7-4). In flow cytometry, biotinylated primary antibodies are typically used in multicolor panels alongside directly conjugated antibodies, followed by streptavidin labeled with a fluorophore such as FITC or PE. A representative protocol stains pig whole blood with PE-conjugated anti-pig CD4a and biotinylated anti-pig CD16 (clone FcG7), followed by Streptavidin-FITC.

A key application unique to the biotin format is cell separation: biotinylated anti-pig CD3ε and CD4 antibodies are explicitly validated for separation assays using streptavidin-conjugated magnetic beads, enabling isolation of specific leukocyte populations for downstream functional studies. Beyond flow cytometry and cell separation, these reagents are used for immunohistochemistry on frozen and formalin-fixed, paraffin-embedded porcine tissues, Western blotting, and immunoprecipitation.