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45 Differences Between IgG and IgM Antibodies


 IgG and IgM Antibodies : Immunoglobulins (Igs), or antibodies, are glycoproteins that are created in response to an immune response and have a unique affinity for the antigens that triggered the response.

The five main classes—IgG, IgM, IgA, IgD, and IgE—each of which has a wide range of subclasses. Each class’s distinctive traits and functions are a result of the H chains’ structural variations. The fact that there are two basic types of L chains—lambda and kappa chains—each of which can be coupled to any of the H chain classes, adds to the immunoglobulins’ already high degree of variability.

The most prevalent class of immunoglobulin is IgG. The blood and tissue fluids have the highest levels of it. Due to its basic four-chain immunoglobulin structure—two identical H chains and two identical L chains—each IgG molecule possesses two identical antigen-binding sites.

 IgG is divided into four subclasses, each of which has unique biological characteristics despite only modest variations in its H chains. IgG provides some immune protection to the developing fetus since it is the only kind of immunoglobulin that can cross the placenta. 

Additionally, these molecules are secreted into the mother’s milk, where they can enter the baby’s system and go to the circulation, where they provide immunity.

The antigen receptor on the surface of mature B cells, known as the IgM form, is the first class of immunoglobulin that is generated by mature B cells.

 When IgM is secreted from the cells, five of the basic Y-shaped units are connected to create a large pentamer protein with 10 antigen-binding sites. The antigenic determinants present in bacterial outer membranes have a high affinity for this large antibody molecule. As a result of this IgM attachment, bacteria clump together or agglutinate.

Detailed Comparison IgG Antibodies vs IgM Antibodies

S.No. Aspect IgG Antibodies IgM Antibodies


Immunoglobulin G (IgG) Immunoglobulin M (IgM)


Monomer Pentamer

Heavy Chain Type

γ (Gamma) μ (Mu)

Molecular Weight

Approximately 150 kDa Approximately 970 kDa


Most abundant antibody class in serum Present in lower concentrations in serum

Maternal Transfer

Crosses the placenta Does not cross the placenta

Neonatal Immunity

Provides passive immunity to fetus/newborn Initial production during neonatal immune response


Longer half-life (about 21 days) Shorter half-life (about 5 days)

Presence in Early Infections

Generally appears later in infections Often the first antibody class produced in response

Complement Activation

Efficiently activates classical complement pathway Less efficient in activating complement


Effective opsonization for phagocytosis Less effective opsonization

Antigen Receptors

Binds to Fcγ receptors on immune cells Binds to different Fc receptors on immune cells

Allergic Reactions

Can mediate allergic reactions Not as commonly associated with allergies

Fetal Protection

Provides long-term protection to the fetus Provides initial defense during early infections


Often indicates past exposure or vaccination Can indicate recent/current infection or primary immune response

Memory Response

Plays a key role in immunological memory Initial response in primary immune response


Developed later in the immune response Developed earlier in the immune response

Secondary Response

Higher concentration in secondary immune response Often less prominent in secondary immune response

Disease Associations

Often associated with chronic infections Early marker of acute infections or recent exposure

Tissue Distribution

Widely distributed in tissues and fluids Present mainly in blood and lymph

Transplacental Transfer

Transferred from mother to fetus Not transferred across the placenta

Role in Autoimmunity

Can contribute to autoimmunity Generally not as involved in autoimmunity

Hemolytic Disease of Newborn

May cause hemolytic disease in Rh-incompatible pregnancies Not as commonly involved in this condition

Blood-Brain Barrier

Can cross the blood-brain barrier Generally does not cross the blood-brain barrier

Immune Complexes

Forms immune complexes with antigens Less commonly forms immune complexes

Primary vs Secondary Immune Response

Often more prominent in secondary immune response Often more prominent in primary immune response


Present in mucosal secretions Not present in mucosal secretions

Rheumatoid Arthritis

Can contribute to the pathogenesis of RA Generally not a major factor in RA

Half-life in Newborns

Short half-life in newborns Relatively longer half-life in newborns

Role in Transplantation

Can be involved in allograft rejection Not as strongly implicated in transplant rejection

Diagnostic Use

Often used in serological tests Used in diagnostics, particularly for acute infections

Bacterial Infections

Involved in immunity to bacterial infections Initial response to bacterial infections

Viral Infections

Plays a role in defense against viral infections Often involved in early viral defense

Rheumatoid Factor

IgG can be targeted by rheumatoid factor Not as commonly targeted by rheumatoid factor


Can be involved in organ transplant rejection Less commonly implicated in transplant rejection

Evolutionary Age

Evolved later in vertebrate immune system More evolutionarily ancient antibody class

Viral Neutralization

Can effectively neutralize viruses Less effective in viral neutralization

Role in Immune Complex Diseases

Implicated in immune complex diseases Less commonly involved in immune complex diseases

Cancer Immunotherapy

Target for some cancer immunotherapies Not as frequently targeted for immunotherapy

Potential Tissue Damage

IgG-mediated immune responses can lead to tissue damage Not as prone to causing tissue damage

Placental Barrier

Can cross the placental barrier Does not cross the placental barrier

B-Cell Receptor

Binds to antigens via B-cell receptor Binds to antigens via B-cell receptor


Can contribute to inflammatory arthritis Not typically associated with arthritis

Antigen-Antibody Complexes

Commonly forms antigen-antibody complexes Forms antigen-antibody complexes less frequently



Frequently Asked Questions (FAQs)

1) Antibodies are made by lymphocytes. Is it real?

B- and T-cells are the two main subtypes of lymphocytes. T-cells kill the body’s own cells that have contracted viruses or developed into cancer, whilst B-cells generate antibodies to attach the pathogen. So, yes, lymphocytes do really generate antibodies.

2) What Are Low Immunoglobulin Levels Indicative Of?

Low immunoglobulin levels indicate that the immune system isn’t functioning as effectively as it should.

Steroids and other immune system-weakening medications may be to blame. problems with diabetes, the state of having damaged or failing kidneys is known as renal disease or kidney failure.

3) Which antigen can pass through the placenta?

The only antibody that passes through the placenta is IgG because of the following reasons.

  • passive immunization that offers babies protection.
  • Bacterial toxins are neutralized by it.
  • It speeds up the phagocytosis process.
  • provides the growing fetus with immunity.

4) After acquiring the mother's antibodies through the placenta, the fetus receives an immunization. This particular vaccination is known as?

Antibody-mediated immunity passed on to a fetus or child by its mother is known as maternal passive immunity, which is a type of naturally acquired passive immunity.

Passive immunity, on the other hand, is acquired protection against infection by the transfer of antibodies to a vulnerable individual. Passive immunity is distinguished from active immunity by the immune system’s response to a pathogen or a vaccine.

Therefore, a newborn’s immunity from the mother’s milk is passive immunity that the body naturally acquired over time.

5) How many IgM molecules include antigen-binding sites?

When IgM is secreted from the cells, five of the basic Y-shaped units are connected to create a large pentamer protein with 10 antigen-binding sites. Particularly adept in attaching to antigenic determinants present on bacterial outer membranes is this large antibody molecule.

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