Thyrotropin-specific binding to human peripheral blood monocytes and polymorphonuclear leukocytes

Area of Science:

• Immunology
• Endocrinology
• Cell Biology

Background:

• Thyrotropin (TSH) is primarily known for its role in thyroid hormone regulation.
• Leukocytes, key immune cells, possess receptors for various hormones, but TSH binding is less understood.
• Investigating non-traditional roles of hormones like TSH in immune responses is crucial for comprehensive understanding.

Purpose of the Study:

• To investigate the binding of thyrotropin (TSH) to different types of leukocytes.
• To determine which leukocyte populations exhibit TSH binding.
• To explore the functional implications of TSH binding to leukocytes, particularly concerning phagocytosis.

Main Methods:

• Preparation of enriched leukocyte subsets including lymphocytes, monocytes, and polymorphonuclear leukocytes using Ficoll-Angiocontrix gradients and Sephadex G-10 adherence.
• [125I]Labeled thyrotropin was used to quantify binding.
• Phagocytosis was assessed by latex bead ingestion to correlate with TSH binding.

Main Results:

• Thyrotropin binding was predominantly observed in monocyte and polymorphonuclear leukocyte preparations.
• High-affinity, low-capacity binding sites for TSH were identified on these leukocytes.
• Equilibrium association constants for TSH binding were comparable to those found in isolated thyroid cells.

Conclusions:

• Leukocytes, specifically monocytes and polymorphonuclear leukocytes, possess functional thyrotropin binding sites.
• Thyrotropin may play a regulatory role in the phagocytic activity of leukocytes.
• These findings suggest a potential interplay between the endocrine and immune systems mediated by TSH.