Researchers discover new role for immune defence cells: They impact hormonal balance

Finnish researchers show in a new study that pituitary macrophages, the immune cells located in the pituitary gland, help regulate hormonal balance. It is possible that in the future, macrophage cells could be used to treat endocrine disorders that can lead, for example, to infertility.

The pituitary gland is a small, pea-sized endocrine gland located at the base of the brain.  The hormones it secretes are involved in almost all major body functions, such as growth, reproduction, water/salt balance, and the regulation of blood pressure and stress. Life is not possible without the hormones produced by the pituitary gland.

“Until now, it has been thought that the pituitary gland receives messages from the rest of the body and increases or decreases hormone secretion accordingly. In fact, macrophages, the immune cells located in the pituitary gland, have a local effect on the cells that produce hormones in the pituitary gland," says InFLAMES Flagship Researcher Heli Jokela from Turku Bioscience Centre and the University of Turku in Finland.

The removal of macrophages revealed their key role in hormone secretion: when the immune cells are removed, the hormone secretion decreases.

Pituitary macrophage cells originate from the fetal period

Macrophages have mostly been thought of as immune defence cells, whose role is to eliminate hostile invaders from tissue. When a virus or another pathogen causes inflammation somewhere in the body, the bone marrow starts to produce monocytes, which turn into the defender cells, i.e. macrophages.

However, not all macrophages originate from the bone marrow and they have more functions than previously thought.

“A particularly novel finding in our study is that all pituitary macrophages originate from the fetal period, rather than from monocytes derived from the bone marrow. They also regenerate themselves to maintain their numbers. The defence cells produced by the bone marrow do not enter the pituitary gland even when there is a sudden inflammation,” explains Doctoral Researcher of the project, Henna Lehtonen.

Leader of the research group, Pia Rantakari, says that, in light of the new discovery about the role of macrophages, it may be possible to use them as a tool to treat human endocrine disorders in the future.

By regulating the macrophages, it could be possible to increase hormone secretion or reduce it if overproduction is the problem.  An example of the latter is PCOS (polycystic ovary syndrome), the most common female hormone disorder. PCOS is associated with increased morbidity and also infertility. However, Rantakari highlights that the therapeutic use of macrophages in endocrine disorders is not yet feasible and requires a great deal of further research.

“By uncovering the roles of immune cells within the pituitary gland, we have not only advanced our understanding of the physiology of the pituitary gland, but have also gained new insights into how immune cells can affect endocrine health," says Rantakari.