3 min read
How many types of antibodies are there?
The human body has five antibody classes. IgG has four subclasses and IgA has two, giving nine constant-region isotypes when subclasses are counted separately.
Matic Broz Computational chemist
Humans have five classes of antibodies: IgG, IgA, IgM, IgD, and IgE. Antibodies and immunoglobulins are two names for the same proteins.
The answer becomes nine if the subclasses of IgG and IgA are counted separately. That still describes broad structural categories, not the enormous number of antibodies that can recognize different targets.
How many classes of antibodies are there?
There are five antibody classes in the human body: IgG, IgA, IgM, IgD, and IgE.[1][2]
The class is set by the constant region of the antibody's heavy chain. This region controls functions such as complement activation and binding to immune-cell receptors. The variable region at the tips of the antibody determines what it binds.[2]
IgM is the first class produced in a primary immune response and is usually secreted as a pentamer. IgD is found mainly on the surface of B cells. IgG is the main class in serum and can neutralize pathogens, mark them for immune cells, and activate complement. IgA protects mucosal surfaces and is common in saliva, tears, and other secretions. IgE binds mast cells and is involved in immediate allergic reactions and defense against parasites.[3]
Changing class does not necessarily change the target. A B cell can replace an antibody's heavy-chain constant region while retaining the same antigen-binding variable region, a process called class-switch recombination.[2]
How many types of IgG are there?
Humans have four IgG subclasses: IgG1, IgG2, IgG3, and IgG4.[1][4]
IgA has two subclasses, IgA1 and IgA2. IgM, IgD, and IgE have no named human subclasses. Counting every class without subclasses once and every IgG and IgA subclass separately produces nine constant-region isotypes.[1]
The chart counts IgG1 through IgG4 and IgA1 through IgA2 separately. Each of the other three classes contributes one isotype.[1]
The subclasses differ in their constant regions, hinge structures, abundance, complement activity, and binding to Fc receptors. IgG1 is the most abundant IgG subclass in serum, but the mix varies with the antigen and the immune response.[3][4]
Which antibody type is most common?
IgG is the most abundant antibody class in human serum.[3][4]
IgA is more prominent at many mucosal surfaces and in external secretions, where it helps protect the respiratory and digestive tracts. The most abundant class therefore depends on which body compartment is measured.[3]
IgG is also the only antibody class that crosses the human placenta in substantial quantities. This transfer provides passive protection to the fetus and newborn.[4]
How many different antibodies can the human body make?
The human preimmune repertoire is estimated to contain at least one trillion, or (10^), unique antibodies.[5][6]
This is a diversity estimate, not the number of antibody molecules circulating at one moment. A healthy adult has about (5 \times 10^9) B cells in peripheral blood, so the circulating population samples only a fraction of the possible repertoire.[5]
B cells create this diversity through V(D)J rearrangement, then pair different heavy and light chains. After exposure to an antigen, somatic hypermutation creates further sequence variants in the antibody's variable domains.[2][6]
Sources▼
- IMGT Index: Receptor type IMGT, the international ImMunoGeneTics information system · July 27, 2026. https://www.imgt.org/IMGTindex/receptor.php
- Structure and function of immunoglobulins Journal of Allergy and Clinical Immunology · 2010. https://pubmed.ncbi.nlm.nih.gov/20176268/
- Structural variation in immunoglobulin constant regions Immunobiology, NCBI Bookshelf · 2001. https://www.ncbi.nlm.nih.gov/books/NBK27106/
- IgG subclasses and allotypes: From structure to effector functions Frontiers in Immunology · 2014. https://pmc.ncbi.nlm.nih.gov/articles/PMC4202688/
- Commonality despite exceptional diversity in the baseline human antibody repertoire Nature · 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6411386/
- The generation of antibody diversity Molecular Biology of the Cell, NCBI Bookshelf · 2002. https://www.ncbi.nlm.nih.gov/books/NBK26860/
Founder and computational chemist, ProteinIQ
Dr. Matic Broz is the founder of ProteinIQ and a computational chemist. He completed a PhD focused on protein structure, molecular dynamics, and neural networks, and writes about structural biology and scientific software.