Thyroid active agents T3 and PTU differentially affect immune gene transcripts in the head kidney of rainbow trout (Oncorynchus mykiss).

In mammals, numerous reports describe an immunomodulating effect of thyroid-active compounds. In contrast, only few reports have been published on this subject in fish. We previously demonstrated that immune cells of rainbow trout (Oncorhynchus mykiss) possess thyroid hormone receptors (THRs) and that exposure of trout to the thyroid hormone 3,3',5-triiodo-l-thyronine (T3) or the antithyroid drug propylthiouracil (PTU) alters immune cell transcript levels of THR and several immune genes. The present study aims to further characterize the immunomodulating action of thyroid-active compounds in trout immune cells. We report here the use of a custom-designed 60-mer oligo immune-targeted microarray for rainbow trout to analyze the gene expression profiles induced in the head kidney by T3 and PTU. Morphometric analyses of the thyroid showed that PTU exposure increased the size of the epithelial cells, whereas T3 induced no significant effects. Both T3 and PTU had diverse and partly contrasting effects on immune transcript profiles. The strongest differential effects of T3 and PTU on gene expressions were those targeting the Mitogen Associated Protein Kinase (MAPK), NFkB, Natural Killer (NK) and Toll-Like Receptor (TLR) pathways, a number of multipath genes (MPG) such as those encoding pleiotropic transcription factors (atf1, junb, myc), as well as important pro-inflammatory genes (tnfa, tnf6, il1b) and interferon-related genes (ifng, irf10). With these results we show for the first time in a fish species that the in vivo thyroidal status modulates a diversity of immune genes and pathways. This knowledge provides the basis to investigate both mechanisms and consequences of thyroid hormone- and thyroid disruptor-mediated immunomodulation for the immunocompetence of fish.