Endocrine Abstracts

The quantification of TSH from a serum or plasma sample constitutes the cornerstone of assessing the thyroid axis in the clinical routine. In addition, T4 and/or T3 levels may be determined to diagnose pathological conditions. However, these data do not necessarily reflect the local action of thyroid hormone in the target tissues and are sensitive to distortion, as best known from pregnancy when chorionic gonadotropin disturbs the regular feedback control. Recently, we identified CD5L as a liver-derived thyroid hormone-responsive biomarker in mice and men, and observed a positive correlation to circulating thyroid hormone in human subjects. [1] In order to enable large-scale clinical analyses, we decided to develop a reliable and robust CD5L-specific sandwich ELISA. To this end, CD5L was recombinantly expressed in HEK293 cells, purified to homogeneity and used to develop monoclonal antibodies. Specificity of the antibodies was tested by commercial CD5L preparations, and a pair of monoclonals was selected for sandwich assay detection that allowed sensitive and robust CD5L quantification. Performance parameters were determined by measuring standard curves four times in double determination; one log level of concentration differences was achieved by a manual assay design, and two log levels were spanned by an automat-based assay design, each with a coefficient of variation below 10% and a relative error below 20%. Stability of CD5L in serum samples was verified by repeated freeze-thaw cycles, and linear dilution experiments indicated reproducible detection over a range of 100- to 32,000-fold with a coefficient of variation below 6%. Given this positive achievement, we are confident to next turn to clinical samples and test whether CD5L assessment may indeed provide the clinically needed additional information on peripheral thyroid hormone action in different and challenging clinical constellations. Supported by the DFG-funded CRC/TR296, LocoTact.

[1] Nock, S., K. Johann, L. Harder, E.K. Wirth, K. Renko, C.S. Hoefig, V. Kracke, J. Hackler, B. Engelmann, M. Rauner, J. Köhrle, L. Schomburg, G. Homuth, U. Völker, G. Brabant, and J. Mittag. 2020. CD5L Constitutes a Novel Biomarker for Integrated Hepatic Thyroid Hormone Action. Thyroid. 30:908-923.