Human immunoglobulin G (IgG) is a part of the immune system that helps to protect the body from infection, and is the most abundant antibody isotype found in the circulatory system. IgG is found in a wide range of bodily fluids, including blood, extracellular fluid, and colostrum, and is also responsible for helping to protect the fetus in utero (“The Importance of IGG in Humans: Its Role and Where It’s Found”). IgG can be prepared in a variety of ways to fit the specific needs of a researcher.
What is IgG?
As stated above, IgG is a key component of the immune system. IgG can be found throughout the body in a range of fluids, such as blood, lymph fluid, cerebrospinal fluid (CSF), and more, and accounts for about 15% of the total proteins found in human serum alongside albumins, enzymes, other globulins, and the like. IgG production is activated as a delayed response to infection, and IgG can be retained in the body for a long time once it is produced. Because of this, IgG can be used as an indicator of previous infection or vaccination of a person if it is detected in the body (“Immunoglobulin IGG Class”).
IgG Subclasses
IgG in serum is classified into four distinct subclasses - IgG1, IgG2, IgG3, and IgG4. These subclasses are distinguished partly based on differences in the protein sequences, but also due to differences in other structural and functional aspects. For example, the subclasses differ in functions related to interactions with IgG-Fc receptors and complement C1q, where IgG1 and IgG3 exhibit the highest affinity and IgG2 and IgG4 having the lowest affinity. The subclasses also vary in structural elements, like in the length of their hinge-regions and in the amount and position of inter- and intrachain disulfide bridges (Wang, Maliepaard, Damelang, Vidarsson, Heck, and Reiding, 2024).
The IgG subclasses are not divided equally in terms of concentration in the body. IgG1 makes up for about 60-65% of the total main subclasses of IgG, while IgG2 makes up for about 20-25%, 5-10% for IgG3, and less than 4% for IgG4. IgG1 can activate the complement cascade by binding to the C1 complex. IgG1 immune responses can be measured in newborns shortly after birth and reach normal concentrations in infancy. IgG2 accounts for immune responses related to carbohydrate and polysaccharide antigens, and normal “adult” concentrations of IgG2 are typically reached by the time someone is 6 or 7 years old. Though found in lower concentrations than IgG1, IgG3 can exhibit higher affinity for C1q making it more effective at activating the complement pathway and plays a major role in immune responses against protein or polypeptide antigens. Though a major subclass of IgG, IgG4 does not bind to polysaccharides, and the exact role of IgG4 in immune responses is still unknown (“Immunoglobulin IGG Class”).
Fractionated IgG
Fractionated IgG is an IgG sample that has been processed and isolated from a sample of plasma or serum. Plasma samples are complex human samples that can contain high concentrations of various proteins which are involved in various bodily functions. Albumin and IgG are the most abundant proteins found in plasma, representing a combined 80% or so of the proteins present. In the process of fractionation, crude source samples are processed into valuable isolates that can be used in various research applications (Burnouf, 2007).
Fractionated IgG samples are used in a variety of research applications. Unsurprisingly, due to the important role of IgG in immune responses, fractionated IgG samples are used extensively in immune research, from use as standards, blocking agents, immunoassay precipitation reagents, and more. Fractionated IgG samples are also used frequently in research that aims to develop new immunotherapies and diagnostic tool development.
Affinity Purified IgG
Another type of IgG preparation is affinity purified IgG. Affinity-purified IgG is a highly refined antibody preparation isolated from serum or plasma using affinity chromatography. In this process, IgG molecules are selectively captured by ligands such as Protein A or Protein G that bind to the Fc region of IgG antibodies. After non-IgG proteins are removed, the purified IgG is recovered, resulting in a preparation with exceptional purity and consistency. Because of this high degree of purification, affinity-purified IgG offers reduced background interference and reliable performance in sensitive analytical applications.
Researchers use affinity-purified IgG in a wide variety of immunological and biochemical assays, including ELISA, Western blotting, flow cytometry, immunohistochemistry, immunoprecipitation, and antibody conjugation. The high purity of affinity-purified IgG is particularly important when antibodies are labeled with enzymes, fluorophores, biotin, or other reporter molecules, as contaminating proteins can reduce labeling efficiency and contribute to nonspecific signal. Affinity-purified IgG is also commonly used as a reference standard, assay control, or starting material to produce conjugated antibodies and other specialized immunological reagents.
Choosing the Right Sample for Your Research
While affinity purification and fractionation are both used to isolate IgG from serum or plasma, they differ significantly in both methodology and outcome. Our proprietary fractionation techniques enrich the IgG fraction by exploiting differences in protein solubility. These methods are efficient and economical, but they do not selectively isolate IgG to the same extent as affinity chromatography. As a result, fractionated IgG preparations retain a broader representation of native serum proteins and immunoglobulins than affinity-purified preparations.
The choice between fractionated and affinity-purified IgG ultimately depends on the intended application. Fractionated IgG is often preferred for bulk applications where high purity is not essential, such as Fc receptor studies, immune complex formation, blocking experiments, complement studies, and other applications requiring large quantities of immunoglobulin at a lower cost. Affinity-purified IgG, on the other hand, is typically selected for applications where maximum purity, reproducibility, and low background are critical. Both products have important roles in research, with fractionated IgG providing a cost-effective source of native immunoglobulins and affinity-purified IgG offering a highly characterized reagent for demanding analytical and research workflows.
If you’re ready to order IgG for your next research project, Innovative Research has the samples you need to make that next discovery. If you’re looking for fractionated IgG samples or affinity purified IgG samples, or looking for samples with labels such as biotin labeled or samples sourced from animals, feel free to browse our catalog and find the perfect sample for your study. If you have any questions, our experienced customer support team is here to help. Reach out to us at sales@innov-research.com to get in touch or place your order today!
Citations
“The Importance of IGG in Humans: Its Role and Where It’s Found.” R&D Systems, www.rndsystems.com/resources/blog/understanding-the-importance-of-human-igg. Accessed 1 June 2026.
“Immunoglobulin IGG Class.” Thermo Fisher Scientific - US, www.thermofisher.com/us/en/home/life-science/antibodies/antibodies-learning-center/antibodies-resource-library/antibody-methods/immunoglobulin-igg-class.html. Accessed 1 June 2026.
Human IgG Subclasses Differ in the Structural Elements of Their N-Glycosylation, Wang, Weiwei, Maliepaard, Joshua C. L., Damelang, Timon, Vidarsson, Gestur, Heck, Albert J.R., Reiding, Karli R., 2024/11/27, ACS Central Science, American Chemical Society, 2374-7943, doi: 10.1021/acscentsci.4c01157, https://doi.org/10.1021/acscentsci.4c01157
“Immunoglobulin IGG Class.” Thermo Fisher Scientific - US, www.thermofisher.com/us/en/home/life-science/antibodies/antibodies-learning-center/antibodies-resource-library/antibody-methods/immunoglobulin-igg-class.html. Accessed 2 June 2026.
Burnouf T. Modern plasma fractionation. Transfus Med Rev. 2007 Apr;21(2):101-17. doi: 10.1016/j.tmrv.2006.11.001. PMID: 17397761; PMCID: PMC7125842.
