Another Fish in the Signaling Sea: The Effect of Thyroid Inhibition on the Immune Function of Adult Fathead Minnows

LeSueur, Meriel

Publication

Another Fish in the Signaling Sea: The Effect of Thyroid Inhibition on the Immune Function of Adult Fathead Minnows

LeSueur, Meriel

Date

2017

Additional date(s)

2017-05-19

Abstract

Over the last few decades, there has been increasing interest and concern regarding the presence and effects of endocrine disrupting compounds (EDCs) in the environment, with a prominent focus on EDCs that disrupt thyroid hormones. Many studies investigating the effects of thyroid hormone disruption have focused primarily on outcomes in growth and metabolism, but recent literature has suggested a role for thyroid hormones in immune system response and regulation. The purpose of this study is to establish the link between thyroid hormone levels and immune system function in the fathead minnow (Pimephales promelas), a prevalent model organism used in toxicology testing, after exposure to the thyroid inhibitor propylthiouracil (PTU). To understand the wide range of effects of thyroid inhibition, measurements were taken at multiple levels of biological organization, and effects were observed at every level in the PTU exposed fish. At the whole organism level, PTU fish were less able to survive pathogen infection relative to the control group. At the tissue level, PTU exposed fish had a significantly lower spleen index and white blood cell counts than control fish, indicating that immune response was impaired. At the molecular level, changes in gene expression of interleukin 1b and interleukin 11 were observed, indicating an alteration at the molecular level. Taken together, this evidence shows that chemically induced thyroid inhibition weakens overall immune function, making the fish less able to mount a successful response. In future toxicological studies, immune function can be used as an end point in monitoring effects of toxic compounds on an organism.