Autoantibodies assays

Comparable reports have prompted a questionnaire investigation of 770 patients with type 2 diabetes at the start of acarbose therapy (62). Patients with one or more susceptibility factors for liver damage underwent ultrasonography and autoantibody assays. There was silent liver disease in 13% and 20 patients had a fatty liver without hepatic disease. In 15% of these patients there were slight reversible changes in transaminase activity after acarbose. 

In CD, autoantibody assays have generally replaced gliadin antibody assays. Measurement of gliadin antibodies is, however, advantageous in small children. Autoantibodies are often absent in CD children under 2 years of age [148, 149]. In another study, antibodies against tTG were found to develop not before an age of 1.3 years [150], Increased concentration of gliadin antibodies may be helpful in the investigation of other... 

The AMD discriminatory accuracy of CEP, CML and pentosidine plasma protein concentrations was compared in a study population of 86. The results showed CEP adducts and CML to be elevated in -69% of the AMD cohort (n = 54) and CEP adducts and pentosidine to be elevated in -74%. CEP autoantibody titer was not informative, due in part to the variability associated with the autoantibody assay and the relatively small sample size. The determined c-statistics suggests that CML and CEP adducts alone discriminate between AMD and control patients with about equal accuracy (-78% to -79%). CML in combination... 

Of 62 initially autoantibody-negative patients treated with interferon alfa for chronic hepatitis C for a mean of 8 months, three developed antibodies to 21b-hydroxylase, a sensitive assay of adrenocortical autoimmunity (528). However, there were no cases of Addison s disease or subclinical adrenal insufficiency. This study suggested that the adrenal cortex is another potential target organ of autoimmune effects of interferon alfa, along with thyroid and pancreatic islet cells. 

Microwave heat-assisted enzyme-linked immunosorbent assay (ELISA) has been used for measuring anti-glomerular basement membrane (GBM) antibodies in kidney serum (Van Dorp et al., 1991) The presence of GBM antibodies is one of the characteristics of Goodpasture s syndrome. The application of microwave heating reduces the duration of incubation to assay circulating anti-GBM autoantibodies. 

Selectivity is the ability of an assay to measure the analyte of interest in the presence of other constituents in the sample. Because IAs are often performed without sample extraction, they are more prone to matrix interference than are chromatographic methods with extraction. Matrix interference could come from crossreactivity with structurally similar components in the sample, or from nonspecific binding to structurally dissimilar components in the matrix. The results are high background noise, loss of sensitivity, and inaccurate and nonreproducible data. Sometimes, the problem may only occur in a few exceptional patient samples that have structurally similar components such as unknown metabolites, or dissimilar components from samples with hyperlipidemia, hemolysis, complement components, rheumatoid factors, binding proteins, autoantibodies, and heterophilic anti-immunoglobulin Ab. 

This volume continues our objective of expanding the intellectual horizon of clinical chemistry. Included are chapters on Clinical Applications of Cytokine Assays Diagnosis and Treatment of Acute Pancreatitis Mitochondrial Mutations and Mitochondrial Diseases Pathobiochemistry of Nephrotic Syndrome Total Antioxidant Capacity Autoantibodies to dsDNA, Ro/SSA, and LaSSB in Systemic Lupus Erythematosis and Lymphoid Malignancies and Immunosuppressive Analysis. The meld of analytical, anatomical, subcellular, and molecular sciences represented by these subjects will continue to evolve and expand. Clinical chemistry is a vibrant and vital profession. Future volumes, their editors, and their contributors will undoubtedly be an important part of the practice and science of clinical chemistry. 

In spite of the strong evidence for the role of DNA/anti-DNA complexes in causing the kidney lesions of systemic lupus (A6, K13, K15, W19), it is not certain that the material assayed in serum as immune complexes is actually composed of DNA linked to specific antibody. Several groups have demonstrated DNA (D2) or anti-DNA (H10) in immune complex material from sera, but careful studies by others have failed to repeat these findings (A7, H27, 18). DNA, by itself, does not persist in the circulation (G10, 17). Because of the multiplicity of autoantibodies found in lupus, any of a number of antigen-antibody systems may be involved (T4). Based on direct examination and the reactivity patterns with various immune complex assays, the immune complex material found in systemic lupus tends to be macromole-cular (>19 S) and complement fixing (A5, A7, C5, D2, El, F12, Gl, L2, M10, N6, T15). 

Sulkanen S, Halttunen T, Laurila K, Kolho KL, Korponay-Szabo IR, Samesto A, et al. Tissue transglutaminase autoantibody enzyme-linked immunosorbent assay in detecting celiac disease. Gastroenterology 1998 115 1322-1328. 

Bockmann J, Winter C, Wittkowski W, Kreutz MR, Bockers TM (1997) Cloning and expression of a brain-derived TSH receptor. Biochem Biophys Res Commun 238 173-1780 Castagiola A, Swillens S, Niccoli P, Dumont JE, Vassart G, Ludgate M (1992) Binding assay for thyrotropin receptor autoantibodies using the recombinant receptor protein. J Clin Endocrinol Metab 75 1540-1544 Cole ES, Lee K, Lauziere K et al. (1993) Recombinant human thyroid stimulating hormone development of a biotech-... 

Autoantibodies and autoimmunity Infliximab may increase the risk of autoimmunity, but the presence of antibodies did not predict the risk of lupuslike syndrome. In trials, the incidence of infliximab-induced anti-double-stranded DNA antibodies ranged from 5 to 34% of patients, depending on the assay method... 

In a study using a competitive radiobinding assay, as many as 43% of patients with rheumatoid arthritis using penicillamine had autoantibodies against insulin (132). These antibodies did not appear to affect pancreatic beta-cells, as the response to intravenous glucose was normal and there were no episodes of hypoglycemia. Other sulfhydryl compounds that have occasionally been reported to cause autoimmune hypoglycemia are tio-pronin, pyritinol, and thiamazole (methimazole) (133). 

The evaluation of certain immunological parameters such as cytokines may also be included. Although, there are currently a limited number of validated assays and understanding regarding the interpretation of this data. Some immune-related biological markers are not necessarily linked to pathological consequences. For example, it is possible to measure autoantibodies.100 However, there is no clear relationship between serum autoantibodies and the risk of autoimmune disease,101 and in the absence of conclusive data, autoantibodies should not be considered a predictive tool.100... 

Many cytokine inhibitors have been described. Among them, soluble receptors or autoantibodies (with affinity constant sometimes being as high as 10 mol/L) can influence cytokine assays. Nonspecific inhibitors are represented by plasma proteins, which bind cytokines (e.g., a2-macroglobu-lin and IL-6). The presence of such inhibitors can contribute to inaccurate results. The half-lifes of cytokines are also very short (generally a few minutes), which explains the very rapid plasma peaks of these molecules. Furthermore, in some instances, a circadian rhythm has been reported (IL-6 and RA) and intraindividual variation is very high (Figure 22-36). 

FT4 assays based on direct equilibrium dialysis or ultrafiltration measure free hormone without the need for total hormone measurements. These methods are unaffected by either variations in serum binding proteins or thyroid hormone autoantibodies. However, IV heparin administration can cause spurious elevations m FT4 determined by these techniques as a consequence of in vitro generation of free fatty acids. Mean values obtained in euthyroid healthy subjects are reported to be slightly higher when using ultrafiltration methods than when using equilibrium dialysis. Analytical performance goals have been recommended for free thyroid hormone assays.When an FT4 assay... 

The enzyme TPO is now recognized as the principal and possibly only autoantigenic component of thyroid micro-somes. Assays based on TPO itself are preferred for routine clinical use in the management of patients with suspected autoimmune disease of the thyroid. Performance of anti-microsomal antibody assays is complicated by the limited availability of human thyroid tissue, the presence of irrelevant thyroid antigens and autoantibodies, and the contamination of microsome preparations with Tg. These complications seem to have been ehminated by using TPO as the antigen. 

Beever K, Bradbury J, Phillips D, McLachlan SM, Pegg C, Goral A, et al. Highly sensitive assays of autoantibodies to fhyroglobulin and to thyroid peroxidase. Clin Chem 1989 35 1949-54. 

Marquet PY, Daver A, Sapin R, Bridgi B, Muratet JP, Hartmann DJ, et al. Highly sensitive immunoradio-metric assay for serum thyroglobulin with minimal interference from autoantibodies. Clin Chem 1996 42 258-62. 

Ruf J, Czarnocka B, Ferrand M, et al. Novel routine assay of thyroperoxidase autoantibodies. Clin Chem 1988 34 2231-4. 

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