The intimate organization of the immune system and endocrine system in the teleost head kidney makes bidirectional signalling between these possible.

The presence of thyroid follicles in the head kidney as a normal, healthy trait in fishes.

In mammals, the pro-inflammatory cytokines TNFα, IL-1β, and IL-6 have, in general, an inhibitory effect on the thyroid system.

The interaction of the thyroid system by paracrine actions of cytokines in the head kidney is likely to be involved in fine-tuning the availability of energy substrates during an immune or stress response.