Homeostatic regulation of the immune response involves factors such as hormones and a functional cross-talk between the endocrine and the immune systems has been well documented. To date, most studies on this relationship were directed mainly to address the role of adrenal hormones and the CRH/ACTH/glucocorticoid axis, whereas scarce information has been obtained regarding the role of thyroid hormones (TH) in immunity; and in fact such studies were mostly conducted on B and T lymphocytes. The majority of TH effects are exerted through TH receptors (TR) which are ligand inducible transcription factors that bind to target genes. The role of antigen presenting cells (APC) is mainly played by dendritic cells (DC) because of their ability to initiate, activate and regulate the immune response. DC are the only APC that stimulate naive T cells and initiate primary immune responses. In vitro, DC can be generated from bone marrow (immature DC), with a retained capability for uptaking and processing antigens. The exposure of these cells to pro-inflammatory stimuli, generates mature DC able to stimulate T cells. The impact of TH on DC functionality still remains unknown. The aim of the present study was to investigate the presence of TR and TR mRNA in DC to forecast TH effects at this level. Mice DC were cultured from bone marrow in the presence of GM-CSF for 7 days. For activation, DC were pulsed with 10 µg/ml lipopolysaccharide (LPS) for the final 18 h of culture. Cells were harvested and TR revealed by immunocytochemistry and TR mRNA by RT-PCR. Results indicated that TR are expressed at both the protein and mRNA levels in immature and mature DC, albeit at lower levels to those expressed on T and B cells.

Conclusions of the Abstract

The presence of TR in DC strongly hints that some specific functions of these cells are regulated by TH. Further studies should provide evidence of TR-regulated DC genes and the function of TH on DC functionality, immunogenicity and tolerance.