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Antibody Structure

Antibody Structure

Overview
Antibodies, also known as immunoglobulins (Ig), are essential players of the adaptive immune system. These antigen-binding proteins are produced by B cells and make up 20 percent of the total blood plasma by weight. In mammals, antibodies fall into five different classes, which each elicits a different biological response upon antigen binding.
The Y-Shaped Structure of Antibodies Consists of Four Polypeptide Chains
Antibodies consist of four polypeptide chains: two identical heavy...

Antibody Structure

Antibody Structure

Overview
Antibodies, also known as immunoglobulins (Ig), are essential players of the adaptive immune system. These antigen-binding proteins are produced by B cells and make up 20 percent of the total blood plasma by weight. In mammals, antibodies fall into five different classes, which each elicits a different biological response upon antigen binding.
The Y-Shaped Structure of Antibodies Consists of Four Polypeptide Chains
Antibodies consist of four polypeptide chains: two identical heavy...

Antibody Structure and Classes

Antibody Structure and Classes

Antibodies, also known as immunoglobulins, are produced by B cells in response to foreign substances, such as bacteria and viruses. These proteins are critical for recognizing and neutralizing these substances, protecting the body from potential harm.
The basic structure of an antibody consists of four protein chains: two identical heavy chains and two identical light chains. These chains are held together by disulfide bonds and other non-covalent interactions, forming a Y-shaped structure.

Immunoglobulin-like Cell Adhesion Molecules

Immunoglobulin-like Cell Adhesion Molecules

Immunoglobulin-like cell adhesion molecules or Ig-CAMs are a versatile group of cell surface glycoproteins belonging to the immunoglobulin protein superfamily. Ig-CAMs possess the characteristic immunoglobulin protein domains and other domains such as the fibronectin type III domain. The Ig domains are glycosylated to varying degrees in different Ig-CAMs.
Ig-CAMs exhibit either homophilic binding (to other Ig-CAMs) or heterophilic binding (to other ligands such as integrins). While most Ig-CAMs...

Complement System

Complement System

The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...

Antibody Actions

Antibody Actions

Antibodies, or immunoglobulins, are critical players in the immune system's arsenal against invading pathogens. Produced by B cells and plasma cells, their primary role is to detect and bind to specific antigens, molecules found on the surface of pathogens like bacteria or viruses. Beyond antigen recognition, antibodies perform several vital functions that contribute to immune defense.
Neutralization
Antibodies can bind to pathogens, preventing them from infecting host cells. This process...

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High-resolution Melting PCR for Complement Receptor 1 Length Polymorphism Genotyping: An Innovative Tool for Alzheimer's Disease Gene Susceptibility Assessment

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Structural difference in the complement activation site of human IgG1 and IgG3.

T E Michaelsen¹, I Sandlie, D B Bratlie

¹Division of Infectious Disease Control, Norwegian Institute of Public Health. terje.e.michaelsen@fhi.no

Scandinavian Journal of Immunology

|November 13, 2009

Summary

Structural differences in the C1q binding site of IgG1 and IgG3 antibodies influence complement activation. Specific mutations reveal IgG3

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Antibody Binding Specificity for Kappa (Vκ) Light Chain-containing Human (IgM) Antibodies: Polysialic Acid (PSA) Attached to NCAM as a Case Study

Antibody Binding Specificity for Kappa (Vκ) Light Chain-containing Human (IgM) Antibodies: Polysialic Acid (PSA) Attached to NCAM as a Case Study

Published on: June 29, 2016

Area of Science:

Immunology
Structural Biology
Complement System

Background:

The C1q binding site on IgG molecules, crucial for complement activation, involves specific residues in the C(H)2 domain.
Human IgG1 and IgG3 are typically the most effective IgG subclasses in activating the complement system.
Understanding structural differences between IgG subclasses is key to elucidating their distinct roles in immune responses.

Purpose of the Study:

To investigate the structural requirements for complement activation by human IgG1 and IgG3 subclasses.
To identify specific amino acid residues responsible for differential complement activation between IgG1 and IgG3.
To explore the functional implications of these structural differences on antibody-dependent complement-mediated lysis (ADCML).

Main Methods:

Generation of NIP-specific IgG1 and IgG3 antibodies with targeted mutations in the C1q binding site.
Assessment of ADCML using target cells with varying antigen concentrations and different complement sources (human, rabbit, guinea pig).
ELISA methods were employed to quantify complement activation, and hinge region truncation was used to assess its impact.

Main Results:

Mutations at Asp(270), Leu(334), and Leu(335) in the C1q binding site revealed significant differences between IgG1 and IgG3.
Alanine substitution at Asp(270) heavily reduced complement activation in IgG1, while only moderately reducing it in IgG3.
These observed differences were independent of the IgG3 hinge region, indicating intrinsic C(H)2 domain variations.

Conclusions:

Human IgG1 and IgG3 possess distinct structural features within their C1q binding sites.
These structural specializations contribute to the differential efficiency of IgG1 and IgG3 in activating the complement system.
The findings provide insights into the functional divergence of IgG subclasses in immune effector mechanisms.