What is the Difference Between IgE and IgG

The main difference between IgE and IgG is that IgE reacts against parasitic infections and allergic reactions that occur with the overreaction of the immune system to the environmental antigens, whereas IgG reacts against bacterial and viral infections. Furthermore, IgE occurs in the lungs, skin, and mucous membranes, while IgG occurs in all body fluids. 

IgE and IgG are two types of antibodies that serve as the major components of humoral immunity. IgE is the least abundant type of antibody, while IgG is the most abundant type of antibody. 

Key Areas Covered 

1. What is IgE
     – Definition, Structure, Importance
2. What is IgG
     – Definition, Structure, Importance
3. What are the Similarities Between IgE and IgG
     – Outline of Common Features
4. What is the Difference Between IgE and IgG
     – Comparison of Key Differences

Key Terms 

Allergy, Antibodies, Humoral Immunity, IgE, IgG, Infections

What is IgE 

IgE or immunoglobulin E is a type of antibody that occurs in mammals. They are the least common type of antibody in the body. Further, plasma B cells produce them. Generally, IgE plays an essential role in the type I hypersensitivity, manifesting various types of allergic reactions. Some examples are allergic asthma, food allergies, most types of sinusitis, allergic rhinitis, and specific types of chronic urticaria and atopic dermatitis.  Additionally, the other environmental allergens against which IgE reacts are anaphylactic drugs, bee stings, pollen, etc.

Figure 1: IgE Structure

Furthermore, IgE plays a major role in parasitic infections by reacting against helminths, including Schistosoma mansoni, Trichinella spiralis, and Fasciola hepatica. It also reacts against parasitic protozoans such as  Plasmodium falciparum.  

What is IgG 

IgG or immunoglobulin G is the most abundant type of antibodies in the body. Generally, in humans, 75% of serum antibodies are IgG. Also, they are the main type of antibodies that occur in the extracellular fluid. Therefore, they play a major role in humoral immunity. Basically, the main function of IgG is to protect the body against infections, which can be either bacterial, viral or fungal.

Figure 2: IgG Structure

Moreover, there are several types of the mechanism of action in IgG. They include opsonization, which coats the surface of antigen by antibodies, agglutination, which immobilize pathogens through binding, the activation of the classic pathway of the complement system, the neutralization of toxins by binding, the activation of the antibody-dependent cell-mediated cytotoxicity, etc. In general, the appearance of IgG antibody occurs after 24-48 hours of antigenic stimulation. 

Similarities Between IgE and IgG 

• IgE and IgG are two types of antibodies or immunoglobulin produced by the immune system of mammals. 
• Plasma B cells produce them. 
• They have a Y-shape and consist of two heavy chains and two light chains. 
• Moreover, they have two antigen-binding sites or paratopes. 
• They are major components of humoral immunity, which is a type of adaptive immunity. 
• Both react against infections and allergens. 

Difference Between IgE and IgG 

Definition 

IgE refers to a class of immunoglobulins, including antibodies, which function especially in allergic reactions while IgG refers to a class of immunoglobulins, including most common antibodies circulating in the blood and facilitating the phagocytic destruction of microorganisms. Thus, this is the fundamental difference between IgE and IgG.

Abundancy 

While IgE is the least abundant type of antibody, IgG is the most abundant type of antibody. 

Occurrence 

IgE occurs in the lungs, skin, and mucous membranes, while IgG occurs in all body fluids.  

Function 

Moreover, their function is the main difference between IgE and IgG. IgE reacts against parasitic infections and allergy reactions, which occur with the overreaction of the immune system to the environmental antigens, whereas IgG reacts against bacterial and viral infections.

Food Allergy/Sensitivity 

Another difference between IgE and IgG is that IgE causes food allergy, while IgG causes food sensitivity. 

Type of Response 

In food allergy, the immune response of IgE is immediate but, does not last longer while in food sensitivity, the immune response of IgG is delayed and lasts longer. 

Type of Hypersensitivity 

Moreover, IgE takes part in the type I hypersensitivity while IgG takes part in the type II hypersensitivity. 

Conclusion 

Basically, IgE is the least abundant type of antibody in the body. Moreover, it mainly reacts to environmental allergens. Additionally, it reacts against parasitic infections. On the other hand, IgG is the most abundant type of antibody in the body. It also reacts against both bacterial and viral infections. Therefore, the main difference between IgE and IgG is their function. 

References:

1. “Immunoglobulin E (IgE): AAAAI.” The American Academy of Allergy, Asthma & Immunology, Available Here.
2. “IgG Antibody.” GenScript, Available Here.

Image Courtesy:

1. “IgE” By SariSabban – Sabban, Sari (2011) Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high- affinity FcεRI receptor (PhD thesis), The University of Sheffield (CC BY-SA 3.0) via Commons Wikimedia   
2. “Anatomy of an IgG” By w:User:AJVincelli – Created by Wikipedia w:User:AJVincelli using PowerPoint 2013 and multiple public reference sources. (Public Domain) via Commons Wikimedia