CLINICAL STUDY Detection of thyroglobulin mRNA transcripts in peripheral blood of individuals with and without thyroid glands: evidence for thyroglobulin expression by blood cells M J Bugalho 1,2 , R S Domingues 2 , A C Pinto 3 , A Garra Äo 1 , A L Catarino 4 , T Ferreira 5 , E Limbert 1 and L Sobrinho 1 1 Servic Ëo de Endocrinologia, 2 Laborato Ârio de Biologia Molecular, 3 Laborato Ârio de Imunologia, 4 Departamento de Patologia Morfolo Âgica and 5 Servic Ëo de Medicina Nuclear, Instituto Portugue Ãs de Oncologia, Lisboa, Portugal (Correspondence should be addressed to M J Bugalho, Servic Ëo de Endocrinologia I.P.O. ± F.G., R.Prof. Lima Basto, 1099-023 Lisboa Codex, Portugal; Email: mjbugalho@ipolisboa.min-saude.pt) Abstract Objective: Recent studies have assigned clinical signi®cance and prognostic value to the detection of thyroglobulin (Tg) mRNA in the blood of patients subjected to total thyroidectomy for a papillary or follicular thyroid carcinoma. In this study, we investigated the diagnostic speci®city of Tg mRNA detection, analysing blood samples from healthy volunteers and from patients previously subjected to total thyroidectomy for reasons other than a carcinoma of the follicular epithelium. Design and Methods: Total RNA was extracted from whole blood, reverse-transcribed and the cDNA ampli®ed for Tg and glyceraldehyde-3-phosphate dehydrogenase with speci®c primers. Expression levels were analysed by using a semi-quantitative PCR. In a few cases, Lymphoprep gradients were used to separate the mononuclear and polymorphonuclear cells prior to further analysis by reverse transcription/PCR. Results: Our data suggested that all individuals expressed Tg mRNA. Moreover, no differences in the expression levels between subjects with and without thyroid glands were documented. Documenta- tion of Tg expression by the mononuclear and polymorphonuclear layers in patients without thyroid glands support 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 thyroid gland, and its expression by normal blood cells should be considered in tests performed for diagnostic purposes. European Journal of Endocrinology 145 409±413 Introduction Clinical interest in serum measurement of thyroglobu- lin (Tg) in the follow-up of patients with well- differentiated carcinomas of the thyroid gland deriving from follicular cells has been largely documented. However, this method is limited by a low sensitivity (1, 2) and by the interference of anti-Tg antibodies (3, 4). In an attempt to overcome the above problems and to increase the sensitivity of detection of residual disease, a reverse transcription/PCR (RT-PCR) approach was developed (5, 6) and appears as to be valuable and promising method for monitoring such patients. The detection of Tg transcripts in normal individuals has been documented (6, 7). This can be tentatively explained either by the presence of follicular cells in circulation, as documented by Ringel et al. (6), or by illegitimate transcription of Tg by blood cells. The importance of the latter possibility has been under- estimated. In order to de®ne the contribution of blood cells to the basal expression of Tg mRNA, we studied two groups of individuals: one comprised healthy volun- teers, and the other comprised patients previously subjected to total thyroidectomy for reasons other than a thyroid carcinoma deriving from follicular cells. Materials and methods Samples EDTA-blood samples were obtained from two groups of individuals: Group A n  10 comprised healthy volunteers; Group B n  10 comprised patients subjected to total thyroidectomy for larynx carcinoma n  2; for multinodular goitre associated with compression of the trachea and paroxysmal dyspnoea n  2; and for medullary thyroid carcinoma n  6: Histological samples were re-evaluated to exclude the presence of a papillary micro-carcinoma. Patients in ISSN 0804-4643 European Journal of Endocrinology (2001) 145 409±413 q 2001 Society of the European Journal of Endocrinology Online version via http://www.eje.org