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

OBJECTIVE: Recent studies have assigned clinical significance 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 specificity 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 amplified for Tg and glyceraldehyde-3-phosphate dehydrogenase with specific 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. Documentation 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.