Glossary
antibody
An antibody is a protein made by plasma cells, derived from activated B cells, that binds one specific antigen and marks it for destruction.
An antibody is a protein produced by plasma cells — the antibody-secreting descendants of activated B cells — that binds to one specific antigen, the molecule the immune system has recognized. Antibodies circulate in blood and lymph and sit on mucosal surfaces, which is why this arm is called humoral immunity.
Binding is the whole mechanism. An antibody does not usually kill anything itself; it neutralizes a toxin or a virus by covering the site it needs, and it marks the target so that complement proteins and phagocytes can finish the job.
Two vocabulary traps follow. An antibody is not the same thing as an antigen: the antigen is the target, the antibody is the weapon made against it. And an antibody is not a cell: B cells make antibodies, but the antibody is a soluble protein, which is why a question about a cell that produces antibodies wants plasma cell.
Antibodies also explain why immunity lasts. Memory B cells from a first exposure respond within hours on a second one, producing a faster and larger wave of antibody — the principle a vaccine borrows when it presents an antigen without the disease.
Taught in
Related terms
- phagocytosis — Phagocytosis is a cell taking in a solid particle by wrapping its membrane around it, then digesting it in a vesicle.
- virus — A virus is genetic material wrapped in a protein coat — it has no cell, no metabolism, and can only reproduce inside a host cell.
Source: The biology guide in this course: its genetics definitions follow the National Human Genome Research Institute's Talking Glossary of Genomic and Genetic Terms, and its process descriptions follow the US National Cancer Institute's SEER Training Modules. Both are US federal government material, not subject to copyright in the United States. The microbiology entries — the bacterial cell, the Gram stain and the chain of infection — were written for this course from the infection-control guidance the biology guide's own source list names (US Centers for Disease Control and Prevention), which the genetics glossary does not cover. The definitions above are written for this course in our own words. (NHGRI Talking Glossary accessed 2026-10-26; definitions written 2026-10-27; the CDC basis for the microbiology entries — Principles of Epidemiology in Public Health Practice, third edition — accessed 2026-10-28, the date the biology guide's own source list records)