Detection of thyroglobulin mRNA transcripts in peripheral blood of individuals with and without thyroid glands: evidence for thyroglobulin expressionby blood cells

Objective: Recent studies have assigned clinical significance and prognosti c value to the detection of thyroglobulin (Tg) mRNA in the blood of patient s subjected to total thyroidectomy for a papillary or follicular thyroid ca rcinoma. In this study, we investigated the diagnostic specificity of Tg mR NA detection, analysing blood samples from healthy volunteers and from pati ents previously subjected to total thyroidectomy for reasons other than a c arcinoma of the follicular epithelium. Design and Methods: Total RNA was extracted from whole blood, reverse-trans cribed and the cDNA amplified for Tg and glyceraldehyde-3-phosphate dehydro genase with specific primers. Expression levels were analysed by using a se mi-quantitative PCR. In a few cases, Lymphoprep gradients were used to sepa rate the mononuclear and polymorphonuclear cells prior to further analysis by reverse transcription/PCR. Results: Our data suggested that all individuals expressed Tg mRNA. Moreove r, no differences in the expression levels between subjects with and withou t thyroid glands were documented. Documentation of Tg expression by the mon onuclear and polymorphonuclear layers in patients without thyroid glands su pport the hypothesis that both lymphocytes and granulocytes express Tg and may justify a background expression in blood, independently of the presence of follicular cells in circulation. Conclusions: Tg mRNA expression is not limited to follicular cells of the t hyroid gland, and its expression by normal blood cells should be considered in tests performed for diagnostic purposes.