HRP-conjugated anti-human primary antibodies are enzyme-labeled immunoreagents for chromogenic, chemiluminescent, and enhanced chemiluminescent (ECL) detection of human antigens. Produced by immunizing hosts such as goat, rabbit, mouse, or rat with purified human immunoglobulins or specific human proteins, the antibodies are affinity-purified and covalently conjugated to horseradish peroxidase (HRP; MW ≈ 40 kDa), a plant-derived glycoprotein with heme prosthetic groups essential for catalytic activity. Conjugation is typically achieved via periodate oxidation, in which carbohydrate residues on the enzyme are oxidized to aldehydes that react with primary amines on the antibody, yielding stable Schiff base linkages. The resulting conjugate maintains an enzyme-to-protein (E/P) molar ratio of approximately 3–5, optimizing catalytic efficiency while preserving antigen-binding affinity.
HRP catalyzes the oxidation of various substrates in the presence of hydrogen peroxide. TMB (3,3',5,5'-tetramethylbenzidine) produces a blue colorimetric product measurable at 450 nm; DAB (3,3'-diaminobenzidine) yields a brown precipitate suitable for immunohistochemistry; and luminol-based substrates generate chemiluminescent emission detectable by X-ray film or digital imaging systems. Available specificities include anti-human IgG (H+L), anti-human IgG (Fc), anti-human IgG (Fab), isotype-specific reagents (IgG1–IgG4, IgA, IgM, IgE, IgD), anti-human CD markers (CD3, CD4, CD8, CD19, CD20, CD25, CD45), cytokines (IL-2, IL-4, IL-6, IFN-γ, TNF-α), and signaling proteins.
Extensive cross-adsorption against serum proteins from mouse, rat, rabbit, goat, and bovine species reduces nonspecific binding in multi-species samples. HRP activity is inhibited by sodium azide, which is commonly used as a preservative; therefore, azide-free buffers are recommended for optimal enzymatic performance.
Applications
Western blotting: HRP conjugates enable sensitive chemiluminescent detection of human proteins separated by SDS-PAGE, with typical dilutions ranging from 1:1,000 to 1:50,000 depending on antigen abundance and substrate sensitivity.
ELISA: HRP conjugates serve as detection antibodies for the quantification of human cytokines, antibodies, hormones, disease biomarkers, and infectious disease markers, including HIV, HBV, and HCV, in serum, plasma, and cell culture supernatants. Chromogenic TMB or chemiluminescent substrates provide sensitive readouts in both direct and sandwich ELISA configurations.
Immunohistochemistry and immunocytochemistry: HRP-mediated deposition of DAB or AEC (3-amino-9-ethylcarbazole) produces permanent precipitates at antigen sites in formalin-fixed, paraffin-embedded tissues, frozen sections, or cultured human cells, enabling morphological analysis by light microscopy.
Dot blot and protein arrays: HRP-conjugated antibodies provide robust detection for screening multiple samples simultaneously. Additional applications include tissue microarrays, in situ hybridization, and enzyme immunoassay (EIA).