Fab Fragment

**Semantic type:** Amino Acid, Peptide, or Protein|Immunologic Factor

**Definition:** Part of an immunoglobulin antibody that binds a specific antigen and consists of both a light chain and part of a heavy chain. By comparison, natural antibodies consist of two heavy and two light chains. An FAB (fragment antibody) offers the advantages of smaller size and lower cross-reactivity compared to the complete antibody. (NCI04)

**Synonyms:** - Antigen Binding Fragment - Fab - Immunoglobulin, F(ab) Fragment