The ELISA technique used for quantitative measurement of serum cytokines uses which specific variant to achieve the highest sensitivity for detecting low concentrations?

• A Indirect ELISA — secondary enzyme-conjugated anti-IgG antibody amplifies signal
• B Competitive ELISA — standard antigen competes with sample antigen for enzyme-conjugated antibody
• C Sandwich (capture) ELISA with matched antibody pairs — antigen captured between two antibodies provides high specificity and sensitivity ✓
• D Direct ELISA — enzyme-conjugated primary antibody directly detects the cytokine

Explanation

Sandwich ELISA (double-antibody sandwich ELISA) is the most widely used format for quantifying cytokines, growth factors, and other proteins in serum/plasma because of its superior sensitivity and specificity. A capture antibody (specific for one epitope) is coated on the plate; the sample antigen binds to it; a second detection antibody (specific for a different epitope on the same antigen) conjugated with enzyme (HRP or AP) then binds to form a 'sandwich'. Signal amplification can be further enhanced with streptavidin-biotin (for biotinylated secondary antibody). Indirect ELISA detects antibodies (not antigen quantitation for cytokines). Direct ELISA is less sensitive because only one antibody amplifies signal. Competitive ELISA is used for small haptens/molecules with single epitopes.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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