Prepubertal gonad investment modulates thymus function: evidence in a teleost fish

The Mediterranean sea bass Dicentrarchus labrax: A marine model species in fish immunology

The Mediterranean sea bass, Dicentrarchus labrax, is a species of great interest due to the extensive knowledge accumulated about its immune system and the application of these findings in aquaculture health management. The available data indicate that sea bass has the morphological and immunological features typical of jawed vertebrates, with minor anatomical differences compared to evolutionarily older teleosts. Namely, all the master genes coding for Tc and Th T cells have been found to be expressed, together with related cytokine families, and Tc/Th activities can be investigated using in vitro models. The B lymphocytes produce IgM/IgT/IgD antibodies in response to antigenic/vaccine stimulation and maintain an IgM-B cell memory for antigens and vaccines. Mucosal and systemic immunity with associated leukocyte populations is present and functional, and it can be modulated by substances added to water or food. Studies on the ontogenesis of immune components defined precise points of lymphocyte development during larval life. Finally, the central nervous system of sea bass has been shown to contain resident lymphocytes, whose number can be modulated by pathogenic infection. Based on the available knowledge summarized in this review, it can be certainly assumed that the Dicentrarchus labrax is a valuable marine model species for studies in immunology and physiology of vertebrates.

Endocrine disrupters affect the immune system of fish: The example of the European seabass

An organism's fitness critically relies on its immune system to provide protection against parasites and pathogens. The immune system has reached its highest complexity in vertebrates, combining the highly specific adaptive with the non-specific innate immunity. In vertebrates, a complex system of steroid hormones regulates major physiological functions comprising energy metabolism, growth, reproduction and immune system performance. This allows the organism to allocate available energy according to life-history traits and environmental conditions, thus maintaining homeostasis and survival of the individual and of the population. Immune system activation must take into account the developmental stage and the nutritional state of the organism. It should respond adequately to different pathogens, but should not overperform or consume all resources for other physiological functions. This important trade-off between immunity and reproduction is balanced by oestrogen. Many of the thousands of chemicals released by humans into the environment, so-called xenobiotics, have the ability to disrupt normal endocrine function. Such endocrine-disrupting chemicals have been demonstrated to impair reproductive functions and to be responsible for numerous diseases in humans and wild life. Given that oestrogens are established modulators of immune cell populations, exogenous oestrogens and oestrogen mimics can modulate immune functions in aquatic animals, such as fish, potentially affecting wildlife and aquaculture. This review highlights the interaction of xenoestrogens with fish immunity. It particularly focusses on the thymus, a major primary immune organ, in the European seabass, Dicentrarchus labrax an important species, both for fisheries and aquaculture.

Proteomic changes in the extracellular environment of sea bass thymocytes exposed to 17α-ethinylestradiol in vitro

The thymus is an important immune organ providing the necessary microenvironment for the development of a diverse, self-tolerant T cell repertoire, which is selected to allow for the recognition of foreign antigens while avoiding self-reactivity. Thymus function and activity are known to be regulated by sex steroid hormones, such as oestrogen, leading to sexual dimorphisms in immunocompetence between males and females. The oestrogenic modulation of the thymic function provides a potential target for environmental oestrogens, such as 17α-ethynylestradiol (EE2), to interfere with the cross-talk between the endocrine and the immune system. Oestrogen receptors have been identified on thymocytes and the thymic microenvironment, but it is unclear how oestrogens regulate thymic epithelial and T cell communication including paracrine signalling. Much less is known regarding intrathymic signalling in fish. Secretomics allows for the analysis of complex mixtures of immunomodulatory signalling factors secreted by T cells. Thus, in the present study, isolated thymocytes of the European sea bass, Dicentrarchus labrax, were exposed in vitro to 30 nM EE2 for 4 h and the T cell-secretome (i.e., extracellular proteome) was analysed by quantitative label-free mass-spectrometry. Progenesis revealed a total of 111 proteins differentially displayed between EE2-treated and control thymocytes at an α-level of 5% and a 1.3-fold change cut off (n = 5-6). The EE2-treatment significantly decreased the level of 90 proteins. Gene ontology revealed the proteasome to be the most impacted pathway. In contrast, the abundance of 21 proteins was significantly increased, with cathepsins showing the highest level of induction. However, no particular molecular pathway was significantly altered for these upregulated proteins. To the best of our knowledge, this work represents the first study of the secretome of the fish thymus exposed to the environmental oestrogen EE2, highlighting the impact on putative signalling pathways linked to immune surveillance, which may be of crucial importance for fish health and defence against pathogens.