Innate immune recognition of the microbiota promotes host-microbial symbiosis

Pattern-recognition receptors (PRRs) are traditionally known to sense microbial molecules during infection to initiate inflammatory responses. However, ligands for PRRs are not exclusive to pathogens and are abundantly produced by the resident microbiota during normal colonization. Mechanism(s) that underlie this paradox have remained unclear. Recent studies reveal that gut bacterial ligands from the microbiota signal through PRRs to promote development of host tissue and the immune system, and protection from disease. Evidence from both invertebrate and vertebrate models reveals that innate immune receptors are required to promote long-term colonization by the microbiota. This emerging perspective challenges current models in immunology and suggests that PRRs may have evolved, in part, to mediate the bidirectional cross-talk between microbial symbionts and their hosts

An Insightful Model to Study Innate Immunity and Stress Response in Deep‐Sea Vent Animals: Profiling the Mussel Bathymodiolus azoricus

Deep‐sea environments are, in some cases, largely unexplored ecosystems, where life thrives driven by the geochemical features of each location. Among these environments, chemosynthesis‐based ecosystems, in the Mid Atlantic Ridge, have an exclusive combination of high depth, high sulfur, and high methane concentrations. This is believed to modulate the biological composition of vent communities and influence the overall vent animal transcriptional activity of genes involved in adaptation processes to extreme environments. This opens, thus, the possibility of finding gene expression signatures specific to a given hydrothermal vent field. Regardless of the extreme physicochemical conditions that characterize deep‐sea hydrothermal vents, the animals dwelling around the vent sites exhibit high productivity and thus must cope with toxic nature of vent surrounding, seemingly deleterious to the animals, while developing surprisingly successful strategies to withstand adverse environmental conditions, including environmental microbes and mechanical stress whether ensuing from animal predation or venting activity. The deep‐sea vent mussel Bathymodiolus azoricus has adapted well to deep‐sea extreme environments and represents the dominating faunal community from hydrothermal vent sites in the Mid‐Atlantic Ridge, owing its successful adaptation and high biomasses to specialized exploitation of methane and sulfide sources from venting activity. Its extraordinary capabilities of adapting and thriving in chemosynthesis‐based environments, largely devoid of photosynthetic primary production and characterized by rapid geochemical regime changes are due to symbiotic associations with chemosynthetic bacteria within its large gills. In an attempt to understand physiological reactions in animals normally set to endure extreme deep‐sea environments, our laboratory has undertaken, for the last few years, a series of investigations, aimed at characterizing molecular indicators of adaptation processes of which components of the host defense system has received most attention. This study reviews recent advances on the characterization of molecules and genes participating in immune reactions, using in vivo and ex vivo models, to elucidate cellular and humoral defense mechanisms in vent mussels and the strategies they have adopted to survive under extreme environments

Current paradigms in immunology

The last decade has seen a revolution in the field of Immunology. Starting from simple views on the ability of the immune system to respond to foreign antigens or to perform self/not-self discrimination, the image has become much more complex, with the realisation that autoreactive lymphocytes normally circulate in the body, without causing harm to the organism. In fact, the critical point in the development of an immune response is the activation of lymphocytes. This depends on the functional state of antigen-presenting cells and on structural features of the so-called "immune synapse". Self/not-self discrimination is therefore not as strict as previously thought: on the contrary, it has been shown that a certain degree of self-reactivity is useful, if not necessary, to the homeostasis of the organism. Furthermore, the immune system can be viewed as a network of elements which try to connect with each other to avoid death, and are endowed with emerging properties. In this review, we will make a quick summary of the "classical" paradigms in Immunology, and will discuss the dogmas (specificity, self/not-self discrimination, tolerance) as well as the new ideas to explain how the immune system works, all of them emerging from experimental observations made in the last decade of immunological research. All this may have interesting consequences both for immunologists wanting to make mathematical models of the Immune System and for those involved in the use of immune algorithms for the development of "Artificial Immune Systems" and computational applications