Recently, the demarcating boundaries that allowed separation of the fields of Endocrinology and Immunology have faded. The missing link that now ties these disciplines together is the understanding that the language by which cells communicate within these two systems is unanimous. This language is the network of products collectively called «cytokines». Cytokines and their specific receptors, initially thought to be exclusively present in the immune system, have recently been shown to be also expressed in the endocrine system. Conversely, numerous studies have demonstrated that a variety of hormones have receptors and exert biologic actions on the immune system. This bidirectional interaction is likely involved in the maintenance of physiological and immunological homeostasis.

The metabolic effects resulting of infection (by bacteria, viruses or parasites) influence a wide variety and number of host biochemical pathways including immune and endocrine responses. The general aim of these modifications is, for the infected host, to control and/or eliminate, the invading organism. On the other hand, the foreign organism has to adapt to these changes of the host`s «milieu» to insure its proper growth and development. In case of the parasite trematode Schistosoma mansoni, arguments leading to the notion that host`s hormones may influence development and survival of the parasite, have emerged.

In this review, we will consider the current state of knowledge concerning the influence of hormones on schistosome settlement and maintenance. We will in addition summerize our recent pieces of work on the role of Interleukin- (IL-) 7 in the development, migration and maturation of the parasite Schistosoma mansoni. IL-7 was first described as a major cytokine for B- and T- cell development and its role - through modifying the host`s hormonal local environment - in S. mansoni infection might enlight an unexpected and new function for Interleukin-7.

Endocrine and Immune systems have long been considered as independent, the first one using hormones as messengers, while the second used cytokines. Hormones were regarded as endocrine substances exerting effects far away from their production site. On the opposite, cytokines were considered as autocrine or paracrine messengers acting locally.

In recent years, many efforts have been undertaken to elucidate the complex interactions between mediators of the endocrine and the immune systems. Numerous studies have demonstrated that a variety of hormones have receptors and exert biologic actions on tissues of the immune system, conversely, cytokines influence the endocrine system (reviewed in (1)).

In this minireview, we would like to summarize some of the bidirectionnal interactions that have been characterized, before concentrating on the role of these connections between both systems in host- pathogen relationships. The field of endocrine- immune system interactions is very large and extremely complex and we are only beginning to comprehend the complexity of it, therefore, examples discussed in this paper are undoubtedly overly simplistic, and will not attempt a comprehensive litterature review.

We will end by summarizing our recent data on infection by the parasite Schistosoma mansoni. Indeed, this will exemplify the interactions between endocrine and immune systems since we showed that schistosomes uses a cytokine (namely interleukin-7 (IL- 7)) and hormones (thyroid hormones) to favour its settlement in the vertebrate hosts.