Diseases ELISA testing

Nowadays, antibodies are utilized in numerous immunoanalytical methods. Those widely used in practice, such as radioimmunoassays, fluoroimmunoassays and enzyme-linked immunosorbent assays (ELISA), require labelled reagents. Millions of ELISA tests for diagnostics of various diseases are daily performed in clinical laboratories. The detection of analytes by two-antibody "sandwich" ELISA, is schematically outlined in Figure 3. 

Fecal elastase 1 concentration can be measured by an ELISA test kit using an antibody specific for the human enzyme pancreatin supplements do not interfere with this pancreatic function test and need not be discontinued. Although measurement of fecal elastase 1 excretion appears to be somewhat more sensitive than fecal chymotrypsin, its specificity and positive predictive value are similarly low, and falsepositive results can be expected in patients with intestinal diseases. Conversely, mild-to-moderate stages of pancreatic exocrine insufficiency cannot be diagnosed reliably. 

Other conditions where HBsAg may not be detected by ELISA are occult HBV infection and HDV-HBV co-infection. ELISA test may also exceptionally exhibit false positivity in individuals with autoimmune hepatitis, pregnant women and chronic liver disease other than hepatitis B infection. 

Antigen-capture enzyme-linked immunosorbent assay (ELISA) testing, IgM ELISA, polymerase chain reaction (PCR), and virus isolation can be used to diagnose a case of Ebola HF within a few days of the onset of symptoms. Persons tested later in the cour.se of the disease or after recovery can be tested for IgM and IgG antibodies the disease can al.so be diagnosed retrospectively in deceased patients by using iminunohistochemistry testing, virus isolation, or PCR. 

Some patients will have repeatedly nonspecific reactivity in an ELISA assay, since the HIV-1 antigen used for the antibody assays is produced in cultured human T cells. It is not unexpected that occasional false positive assays occur in human sera from individuals with autoimmune diseases a history of multiple pregnancies or multiple transfusions or antibodies to certain class II histocompatibility antigens (especially HLA-DR4). Block reagents have been added to specimen diluents to minimize cross-reactions in these sera. This necessitates the use of confirmatory tests, especially the Western blot. With the use of both ELISA and Western blots, false positives decrease to less than 1 per 100,000. 

A number of commercial antibody-based microarrays for multiplexed cytokines analysis are now available (Beckman Coulter BD Biosciences Panom-ics Pierce S S Zyomyx and others). Cytokines are essentially biomarkers of cell injury, inflammation, and apoptosis. They are released by cells in culture in response to drug action (Turtinen et al., 2004) or are elevated in serum in various disease states. Moreover, numerous cytokines are involved in cellular response and many serve as dual effectors (Asao and Fu, 2000). As a result, anticytokine microarrays are being evaluated in drug discovery for off-target toxicity testing to replace standard ELISA plate formats. 

LCAT acts preferentially on lipids transported by HDL (so-called a-LCAT activity), but also on lipids transported by apoB-containing lipoproteins (so-called jS-LCAT activity) [58, 85]. In practice, LCAT activity is measured either as the activity required to esterify radioactive cholesterol that has been exogenously incorporated into native HDL or into artificial HDL-like particles (a-LCAT activity) or which has been equilibrated with endogenous lipoproteins of the plasma sample (cholesterol esterification rate, CER) [21, 58, 85]. Several variations of these assays have been reported, some of which are available as commercial test kits (e.g., Roar Biomedical, New York, USA). In addition, LCAT concentration can be determined by either laboratory-made tests or by a commercial ELISA kits [57]. However, the decrease in LCAT concentration is difficult to judge since it also decreases secondary to HDL deficiency due to causes other than LCAT deficiency. Plasma from patients with LCAT deficiency fails to esterify radioactive cholesterol provided by any substrate. By contrast, plasmas of patients with fish-eye disease show a near-normal cholesterol ester-fication rate but have a selective inability to esterify radioactive cholesterol provided to plasma with native HDL or reconstituted HDL (a-LCAT activity) [58, 85]. 

Advances in technology have made the increases in number and repertoire possible. The introduction of the radioimmunoassay (RIA) by Yalcw and Berson in 1958 has been recognized by a Nobel Prize (1). The technology was made more assessable for inspection needs by the development of the enzyme-labeled immunosorbent assay (ELISA), by Engvall and Perlmann in 1971 (2) Many innovations since 1971 have resulted in portable, easy-to-use, disposable formats. The simplicity of the innovative formats for testing and the wide spectrum of applicable analytes accommodated by antibody diversity make immunoassays one of the most attractive technologies for the detection of disease, harmful chemicals and toxins, and economic fraud such as species substitution. 

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