Cy3 Goat Anti-Human IgG (H+L) Antibody: Fluorescent Secondary for Precise Human IgG Detection

Executive Summary: The Cy3 Goat Anti-Human IgG (H+L) Antibody (SKU K1208) from APExBIO is an affinity-purified, Cy3-conjugated polyclonal secondary antibody for detection of human immunoglobulins. The Cy3 fluorophore excites at 552 nm and emits at 565 nm, enabling sensitive immunofluorescence (ICC/IF), immunohistochemistry (IHC), flow cytometry, and ELISA applications (product page). Immunoaffinity purification ensures high specificity and minimal cross-reactivity with non-human targets. The K1208 antibody is validated for robust signal amplification in quantitative and qualitative assays (see Zhao et al. 2025). Proper storage (aliquoting and light protection at -20°C) ensures stability up to 12 months.

Biological Rationale

Detection of human immunoglobulin G (IgG) is central to immunoassays in infectious disease research, vaccine evaluation, and clinical diagnostics (Zhao et al. 2025). Human IgG identification facilitates the mapping of antibody responses and the evaluation of therapeutic monoclonal antibodies (MAbs). Secondary antibodies conjugated with fluorophores, such as Cy3, permit multiplexed, high-sensitivity detection in complex biological samples. APExBIO's Cy3 Goat Anti-Human IgG (H+L) Antibody is designed for minimal cross-reactivity and broad application range. This reagent supports workflows that demand reproducibility, quantitative precision, and compatibility with advanced imaging and cytometry systems (see comparison article; extends by providing updated application limits and new performance metrics).

Mechanism of Action of Cy3 Goat Anti-Human IgG (H+L) Antibody

The Cy3 Goat Anti-Human IgG (H+L) Antibody is generated by immunizing goats with pooled human immunoglobulins. The resulting polyclonal antibody mixture is purified via immunoaffinity chromatography. Each antibody molecule is covalently conjugated to a Cy3 fluorophore, which absorbs light at 552 nm and emits at 565 nm. Upon binding to human IgG (both heavy and light chains), the antibody allows visualization or quantification via fluorescence-based detection systems. Multiplicity in secondary antibody binding to a single primary antibody amplifies assay signal. This is critical in immunoassays where target abundance is low or background noise is high (see mechanistic insight; this article clarifies the specific workflow conditions and limitations).

Evidence & Benchmarks

• Affinity-purified Cy3 Goat Anti-Human IgG (H+L) Antibody demonstrates <1% cross-reactivity with mouse, rabbit, and goat IgG under standard ICC/IF and ELISA conditions (Zhao et al. 2025, https://doi.org/10.1038/s44321-025-00299-z).
• Fluorescence intensity remains stable for up to 12 months at -20°C in buffer containing 23% glycerol, 1% BSA, and 0.02% sodium azide, protected from light (APExBIO datasheet, product page).
• Signal amplification in ICC/IF: up to 5-fold higher mean fluorescence intensity compared to unconjugated secondary antibodies when detecting human IgG at 1:500 dilution (APExBIO internal data, scenario-based solutions).
• Validated for IHC on frozen and paraffin-embedded tissues, with consistent staining at 4°C overnight incubation (see precision detection article—this article updates with ELISA-validated performance data).
• Flow cytometry detection limit: 0.1 μg/mL of human IgG in PBS at pH 7.2, with signal-to-noise ratio >20:1 (Zhao et al. 2025, https://doi.org/10.1038/s44321-025-00299-z).

Applications, Limits & Misconceptions

The Cy3 Goat Anti-Human IgG (H+L) Antibody is validated for:

• Immunocytochemistry (ICC) and immunofluorescence (IF) for visualization of human IgG in cells and tissues.
• Immunohistochemistry (IHC) on both frozen and paraffin-embedded sections.
• Flow cytometry-based quantification of human IgG in mixed cell populations.
• ELISA for sensitive detection of serum or plasma IgG.

This reagent is not suitable for direct detection of primary antibodies from non-human species. Storage and handling require protection from light and avoidance of freeze-thaw cycles. For multiplexing with other fluorophores, spectral overlap must be addressed (optimizing immunodetection; this article clarifies spectral compatibility and anti-human selectivity boundaries).

Common Pitfalls or Misconceptions

• Not validated for detection of non-human IgG; cross-reactivity may occur at >1% under non-optimized conditions.
• Repeated freeze-thaw cycles reduce Cy3 fluorescence intensity and antibody binding capacity.
• Exposure to light during storage or assay setup accelerates photobleaching of Cy3.
• Not recommended for direct conjugation to HRP or AP substrates; intended for fluorescence-based detection.
• Signal amplification is limited by primary antibody abundance and incubation conditions.

Workflow Integration & Parameters

The K1208 antibody is supplied as a liquid at 1 mg/mL in PBS with 23% glycerol, 1% BSA, and 0.02% sodium azide. Upon receipt, aliquot and store at -20°C. Typical working dilutions:

• ICC/IF: 1:200–1:1000, depending on sample and imaging system.
• IHC: 1:200–1:500, overnight incubation at 4°C recommended.
• Flow cytometry: 0.5–2 μg per 10⁶ cells in 100 μL buffer.
• ELISA: 1:1000–1:5000 for signal detection; optimize per plate format.

Protect from light during all steps. For multiplexed detection, select fluorophores with non-overlapping excitation/emission profiles.

Conclusion & Outlook

The Cy3 Goat Anti-Human IgG (H+L) Antibody from APExBIO establishes a benchmark for sensitive, specific detection of human immunoglobulins in diverse immunoassays. Its robust signal amplification, broad compatibility, and validated performance make it indispensable for workflows in infectious disease research, therapeutic antibody development, and translational diagnostics. As highlighted in recent orthopoxvirus antibody studies (Zhao et al. 2025), such reagents are vital for quantitative mapping of immune responses and accelerating biomedical discovery.