Antibody
Definition
An immunoglobulin (typically IgG) raised to bind a specific antigen. Source decides specificity: polyclonal antibodies recognise many epitopes, monoclonal antibodies recognise one.
- Typical class
- Immunoglobulin G (IgG)
- Polyclonal
- Recognises multiple epitopes on an antigen
- Monoclonal
- Recognises a single epitope, higher specificity
- Forensic role
- Basis of species, blood group, and drug immunoassays
Common questions
Why does a forensic assay sometimes use a monoclonal antibody instead of polyclonal?+
A monoclonal antibody binds one defined epitope, which reduces cross-reactivity with related proteins and gives a more reproducible result across batches, whereas a polyclonal antiserum can vary between production runs and animals.
What limits an antibody-based test's reliability on old or contaminated evidence?+
Protein degradation, microbial activity, and environmental exposure can destroy the epitope the antibody targets long before the sample is otherwise unusable, producing a false negative even when the original substance was present.
Related terms
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Competitive vs Non-Competitive Format
- Competitive: labelled antigen and sample antigen compete for a limited number of antibody sites; signal is inversely proportional to analyte. Non-competitive (sandwich):...
- ELISA
- Enzyme-Linked Immunosorbent Assay. Heterogeneous, plate-based, enzyme label (HRP, alkaline phosphatase), colour or chemiluminescent readout. Four standard formats: direct, indirect, sandwich, competitive.
- Epitope and Hapten
- Epitope is the small surface patch on an antigen the antibody actually binds. A hapten is a small molecule (most drugs of...
- Homogeneous vs Heterogeneous
- Homogeneous assays (EMIT, FPIA) need no wash step, so they run fast on clinical analysers. Heterogeneous assays (ELISA, RIA) require a wash...
- Label
- The reporter coupled to either the antigen or the antibody so the binding event becomes measurable. Three families dominate: radioisotopes (RIA), enzymes...
- Lateral-Flow Immunoassay
- A point-of-care competitive immunochromatographic format on a nitrocellulose strip. In the absence of drug, colloidal gold-labelled antibody is captured at a test...
- RIA
- Radioimmunoassay. Berson and Yalow, 1959. Heterogeneous, competitive, radioisotope label (most often 125-I). Highest sensitivity historically, now displaced in most Indian labs by...