XXIst scientific meeting of the Italian Association of Developmental and Comparative Immunobiology (IADCI), 12 - 14 February 2020, Department of Biotechnology and Life sciences (DBSV), University of Insubria, Varese, Italy

The immune defence system of vertebrates in its molecular and cellular components is remarkably conserved from teleost fish, the more ancient extant representatives at the base of the evolutionary lineage that brings to mammals. Multiple observations support the hypothesis that a layered system of immune responses accumulated among vertebrates over evolution, and lower layers behave as the immune system actually present in extant fish species. In this view, lymphocytes are classified as responsible of acquired responses, but recent evidences show that mammalian lymphocyte subpopulations may behave as innate cells, engaging non-self rapidly and without antigen presentation. Innate-like lymphocytes i) maintain gut homeostasis and provide early responses to intestinal infections, ii) are involved in autoimmune diseases and cancer iii) are able to combat non-self in a MHC-independent fashion, iv) produce unbiased natural polyreactive antibodies, v) are associated to typical cytokine patterns. The main lymphocyte subpopulations displaying innate-like activities in mammals have been identified as B1-B cells, -T cells, MAIT cells, and NKT cells. Our research focuses on the spatial and temporal origin of fish lymphocyte populations, on their in vitro activities, and on the molecular and morphological signatures of fish lymphocytes. The aim is to predict knowledge related to mammalian innate lymphocytes from fish lymphocytes and to model human diseases. This review will present evidences suggesting the similarities between fish lymphocytes and mammalian innate-like lymphocytes. Acknowledgements Department of Excellence-2018” Program (Dipartimenti di Eccellenza) of the Italian Ministry of Education, University and Research, DIBAFDepartment of University of Tuscia, Project “Landscape 4.0 – food, wellbeing and environment”.