Monoclonal antibodies: diagnostic and laboratory uses
Infection and response • Monoclonal antibodies (biology only) (HT only)
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Definition and specificity of monoclonal antibodies
Monoclonal antibodies are identical antibody molecules produced from a single cloned cell line and designed to bind one specific antigen shape. High specificity causes binding only when the matching antigen is present, which reduces cross-reaction with unrelated molecules. The single-target nature makes monoclonal antibodies reliable reagents for tests that require precise recognition of a hormone or a pathogen protein.
Pregnancy tests - cause and detectable effect
The pregnancy hormone HCG appears in urine soon after implantation in early pregnancy. Monoclonal antibodies fixed to a test strip bind HCG molecules in the urine; binding causes a labelled complex to accumulate at a visible test line, producing a colour change and indicating pregnancy. The presence of HCG causes formation of the antibody–antigen complex and the visible signal; absence of HCG leaves the test line blank. This mechanism allows detection of very small HCG concentrations.
Laboratory measurement of hormone levels
Laboratory immunoassays use monoclonal antibodies to capture or label hormones in blood or other samples. Capture antibodies immobilise the hormone and a second labelled antibody produces a measurable signal (colourimetric, fluorescent or radioactive). The signal strength correlates with hormone concentration, so cause (antibody binding) produces an effect (proportional signal) that instruments quantify. Consistent hybridoma-derived antibodies ensure reproducible standard curves for accurate concentration measurement.
Detection of pathogens and limiting factors
Monoclonal antibodies detect pathogen-specific proteins (antigens) by binding surface proteins on viruses, bacteria or infected cells; binding allows rapid tests or laboratory assays to signal pathogen presence. Limiting factors include antigen variation (mutations that change the target shape), low antigen concentration below detection limits, and cross-reactive antigens that cause false positives. Laboratory validation, appropriate controls and use of multiple antibodies against different antigens reduce these limitations.
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