Overview
Immunoglobulin G (IgG) is the predominant antibody isotype in human serum, accounting for 75-80% of total immunoglobulins. It consists of two heavy chains (γ-type) and two light chains, forming a Y-shaped structure with antigen-binding Fab regions and a constant Fc region. IgG is produced by plasma cells in secondary immune responses and provides long-term immunity through neutralization, opsonization, and complement activation. Four subclasses exist in humans (IgG1-4), each with distinct biological functions. IgG crosses the placenta, providing passive immunity to fetuses, and has the longest half-life (21 days) among antibodies due to neonatal Fc receptor recycling. Its stability and versatility make it indispensable in medical and research applications.
Physical and Chemical Properties
IgG molecules have a molecular weight of approximately 150 kDa and an isoelectric point ranging from 6.0 to 8.0 depending on subclass. They exhibit high solubility in physiological buffers (PBS, Tris-HCl) but may precipitate at high concentrations (>50 mg/mL). The antibody maintains stability between pH 4-9 and at temperatures up to 60°C for short periods. Lyophilized IgG can be stored for years at -20°C, while liquid formulations typically require 2-8°C storage with carrier proteins (e.g., BSA) to prevent adsorption. Aggregation is a common degradation pathway, detectable by size-exclusion chromatography. The Fc region contains N-glycosylation sites critical for effector functions.
Main Applications
In diagnostics, IgG serves as the primary detection antibody in ELISA, Western blotting, and immunohistochemistry due to its high specificity. Therapeutic IgG formulations treat immune deficiencies (IVIG), autoimmune diseases (anti-TNFα), and cancers (rituximab). Neutralizing IgG antibodies are crucial in antiviral therapies and vaccine development. Research applications include flow cytometry, immunoprecipitation, and blocking experiments. Monoclonal IgG antibodies dominate the biologics market, with over 100 FDA-approved products. Emerging uses include antibody-drug conjugates (ADCs) and bispecific antibodies that leverage IgG's modular structure.
Safety and Storage
IgG products are generally non-toxic but may contain trace contaminants (endotoxins, host cell proteins) requiring validation. Proper handling includes using endotoxin-free tubes and avoiding repeated freeze-thaw cycles. Lyophilized IgG should be reconstituted with sterile, deionized water or specified buffers. Storage at 2-8°C in dark conditions prevents light-induced degradation. For long-term preservation, aliquotting and storage at -20°C (with 50% glycerol for frequent use) is recommended. SDS-PAGE analysis should confirm purity, while functionality tests (ELISA binding) verify activity post-storage.
B2B Procurement Guide
Bulk IgG procurement requires evaluation of: (1) Source material (human serum, recombinant expression systems), (2) Purity level (research-grade ≥90%, diagnostic/therapeutic ≥95%), (3) Subclass/isotype specificity, and (4) Validation data (certificates of analysis). Suppliers should provide detailed characterization including SDS-PAGE, HPLC purity profiles, endotoxin levels, and functional testing. For therapeutic applications, cGMP compliance and regulatory documentation are essential. Large-volume buyers (pharma companies) may negotiate contracts with tiered pricing, while research institutions often utilize distributor networks for smaller quantities.
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