Thyroid Nodule Colloid Is Associated With a Pro‐Inflammatory Response in THP‐1‐Derived Macrophages: An Exploratory In Vitro Study

BACKGROUND: Benign thyroid nodules are common, but the contribution of the intranodular microenvironment to local inflammation remains incompletely understood. Thyroid colloid has traditionally been regarded primarily as a reservoir for thyroid hormone precursors, although it may also contain inflammatory mediators. We therefore explored the response of THP-1-derived macrophages to colloid obtained from benign thyroid nodules and compared this response with exposure to matched patient serum and healthy donor serum. METHODS: Thyroid colloid and serum samples (n = 10) were collected from patients undergoing hemithyroidectomy for benign nodules. Additionally, serum samples from age- and sex-matched healthy controls (n = 10) were obtained. They were centrifuged at 1500 rpm for 10 minutes and stored at -80°C. THP-1 monocytes were differentiated into macrophages using phorbol-12-myristate-13-acetate (PMA) and exposed to thyroid colloid, matched patient serum, or healthy donor serum. Expression of M1-associated (IL12 B, IL23 A, NOS2, and CD80) and M2-associated (ARG1, CD206, CD163, CD68, and IL10) genes was quantified by quantitative real-time PCR. Cytokine secretion was determined using an enzyme-linked immunosorbent assay. RESULTS: THP-1-derived macrophages exposed to thyroid nodule colloid showed significant upregulation of M1-associated markers, including IL12 B, IL23 A, NOS2, and CD80, compared with macrophages exposed to patient serum or healthy donor serum. Expression of several M2-associated genes, including IL10, CD163, and CD68, was reduced following colloid exposure. Colloid-exposed macrophages also showed higher secretion of IL-1β, IL-6, and IL-17, whereas IL-10 levels remained unchanged. These findings indicate a pro-inflammatory M1-associated transcriptional and secretory response to thyroid nodule colloid under the present in vitro conditions. CONCLUSIONS: Exposure to benign thyroid nodule colloid was associated with a pro-inflammatory M1-associated response in THP-1-derived macrophages in vitro. Because non-nodular thyroid colloid was not available as a biologically matched comparator, these findings cannot establish that this response is specific to nodule-derived colloid or that colloid is a causal driver of inflammation in vivo. Studies using non-nodular thyroid comparators and primary patient-derived macrophages are required to validate the specificity and biological relevance of this observation. TRIAL REGISTRY REGISTRATION NO: 8638 dated January 22, 2023.