Short answer
An antigen is something the immune system can recognize, such as a molecular feature on a pathogen. An antibody is a protein produced by B cells that can bind a particular antigen. The antigen is the target in this relationship; the antibody is one immune response to it. 1 2
An antibody can bind an antigen; they play complementary roles in immune recognition.
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At a glance
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| Question | Antigen | Antibody |
|---|---|---|
| Role | Recognized target | Binding immune protein |
| Can come from | Pathogen, allergen or host material | B cells |
| Simple analogy | Lock feature being recognized | Matching binding tool |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Antigen. A molecule or molecular feature recognized by the immune system. 1
Antibody. An immune protein made by B cells that binds a particular antigenic target. 2
Key differences
Antigen and antibody are not interchangeable chemicals. Antigens may be parts of microbes, allergens or even the body’s own cells. Antibodies have structures that recognize particular targets; binding can help other immune processes act, but binding alone is not the whole immune response. 1 2
How to tell them apart
In a sentence, ask which object is being recognized and which immune protein does the recognizing. A test that detects an antigen seeks a target molecule; a test that detects antibodies looks for the body’s response. The two tests answer different timing and exposure questions. 1 2
Where they overlap
Both can be present in the same infection or vaccination story. Their interaction is central to adaptive immunity, and some assays rely on antibody binding to detect antigen. 1 2
Edge cases
“Antigen” does not mean “foreign” in every context; self-antigens matter in autoimmunity. An immune response need not produce a useful or protective antibody, and antibodies are only one part of immunity. 1 2
Why the distinction exists
The distinction separates a target from a response molecule. That separation makes vaccine mechanisms, diagnostic assays and allergic reactions easier to describe accurately. 1 2
Common misconceptions
An antigen is not an antibody made by a pathogen. Pathogens can carry antigens; the host’s B cells make antibodies. 1 2
Examples
A viral surface molecule may act as an antigen. A B cell can produce an antibody that binds that molecule; the molecule and the binder are different things. 1 2
Sources
Sources checked October 3, 2026.
- National Institute of Allergy and Infectious Diseases — Immune Cells. Antigen presentation; B cells.
- National Human Genome Research Institute — Antibody. Definition and narration.