ELISA tests available for the detection of antibodies to infectious agents are sensitive and specific. As described in depth in Chapter 9, the presence of a specific antibody is detected by the ability of a second antibody, conjugated to a colored or fluorescent marker, to bind to the target antibody, which is bound to its homologous antigen. (Various enzyme-substrate systems, including the use of avidin-biotin to bind marker substances, are also dis cussed in Chapter 9.) The antigen to which the antibodies bind, if antibodies are present in the patient’s sera, is either attached to the inside of the wells of a microtiter plate, adherent to a filter matrix, or bound to the surface of beads or plastic paddles. Advantages of ELISA tests include ease of performance on many serum samples at the same time and easy detection of the colored or fluorescent end products with appropriate instrumentation, removing the element of subjectivity inherent in so many serologic procedures. Disadvantages include the need for special equipment, the fairly long reaction times (often hours instead of minutes for particle agglutination tests), the relative end point of the test (which relies on measuring the amount of a visible end product that is not dependent on the original antigen-antibody reaction itself but on a second enzymatic reaction, compared to a directly quantitative result), and the requirement for batch processing to ensure cost effectiveness.

Commercial microdilution or solid-phase matrix systems are available to detect antibody specific for hepatitis virus antigens, herpes simplex viruses 1 and 2, respiratory syncytial virus (RSV), cytomegalovirus, human immunodeficiency virus (HIV), rubella virus (both IgG and IgM), mycoplasmas, chlamydiae, Borrelia burgdorferi, Entamoeba histolytica, and many other agents.

The introduction of membrane-bound ELISA components has improved sensitivity and ease of use dramatically. Slot-blot and dot-blot assays force the target antigen through a membrane filter, causing it to become affixed in the shape of the hole (a dot or a slot). Several antigens can be placed on one membrane. When test (patient) serum is layered onto the membrane, specific antibodies, if present, bind to the corresponding dot or slot of antigen. Addition of a labeled second antibody and sub sequent development of the label allows visual detection of the presence of antibodies based on the pattern of antigen sites. Cassette-based membrane-bound ELISA assays, designed for testing a single serum, can be per formed rapidly (often within 10 minutes). Commercial kits to detect antibodies to Helicobacter pylori, Taxoplasma gondii, and some other infectious agents are available.

Antibody capture ELISAs are particularly valuable for detecting IgM in the presence of IgG. Anti-IgM anti bodies are fixed to the solid phase; therefore, only IgM antibodies, if present in the patient’s serum, are bound. In a second step, specific antigen is added in a sandwich format and a second antigen-specific labeled antibody is added. Toxoplasmosis, rubella, and other infections are diagnosed using this technology, typically in research settings.

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مواضيع ذات صلة

Blood Coagulation Tests

Western Blot Immunoassays

Indirect Fluorescent Antibody Tests and Other Immunomicroscopic Methods

Laboratory Diagnosis of Thyrotoxicosis

Laboratory Findings of Beta-Thalassemia Syndromes

Complement Fixation Assays

Flocculation Tests

Particle Agglutination Tests

Direct Whole Pathogen Agglutination Assays

Separating IgM From IgG For Serologic Testing

Serodiagnosis of Infectious Diseases

TSH- Receptor Antibodies