Respuestas inmunes adaptativas en trucha arcoíris (Oncorhynchus mykiss): respuesta a diferentes antígenos y caracterización de subconjuntos de células B en mucosas

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología. Fecha de lectura: 12-11-2021From an evolutionary point of view, fish constitute the first animal group in which all elements of the adaptive immune system are present, however, still, many differences between the mammalian and the teleost adaptive immune systems are found. Among the most important differences are that teleost fish lack bone marrow, the main hematopoietic tissue in mammals, as well as germinal centers (GCs) and lymph nodes. In mammals, GCs are microenvironments in which B cells closely interact with cognate T helper cells and follicular dendritic cells and differentiate to long-lived plasma cells during T-dependent (TD) responses. In contrast, non-switched IgM antibody responses, which occur extrafollicularly (outside GCs), generate short-lived IgM plasma cells that produce antibodies of low affinity that interfere with pathogens and limit their expansion while follicular high-affinity responses are mounted. These extrafollicular responses are mainly orchestrated by mammalian innate-like B lymphocytes, namely B1 B cells and marginal zone (MZ) B cells, during T-independent (TI) responses. Interestingly, recent evidence points to a phenotypical and functional resemblance of fish B cells with mammalian B1 cells, as both B cell subsets produce high amounts of natural IgM antibodies, present a strong phagocytic capacity, recognize pathogens through Toll-like receptors (TLRs) and express low surface IgD and high surface IgM, among other similarities. This together with the fact that fish lack lymph nodes, GCs and specialized immunoglobulins (Ig) such as IgG, IgA or IgE, led us to think that fish B cell responses could best resemble mammalian extrafollicular IgM TI responses. In this context, in this Thesis, we explored how teleost fish B cells responded to different types of antigens, using model antigens that have been classified in mammals according to whether they require or not T cell help to fully activate B cells. These experiments were performed in rainbow trout (Oncorhynchus mykiss), first in vitro using splenic B cells and afterwards in vivo administering the antigens through different routes (anal or intraperitoneal). Finally, the second main objective of this Thesis was to contribute to a full characterization of the B cells that are present in different segments of the intestinal mucosa. All the results obtained will contribute to a better understanding of how teleost B cells respond to different types of antigens, also providing us with more insights on the different B cell subsets that colonize fish mucosal surfaces. The information provided will be of great importance for the rational development of effective vaccines for aquaculture in the futureThe work presented in this Thesis has been funded by the following projects: European Research Council (ERC) Consolidator Grant 2016 (TEMUBLYM 725061); AGL2014-54456-JIN from the Spanish Ministry of Economy and Competitiveness; AGL2017-85494-C2-1-R from the Spanish Ministry of Science, Innovation and Universities; and 2016-T1/BIO-1672 grant from the Autonomous Community of Madrid. Alba Martín Martín has been funded by a FPI-SGIT-2016 fellowship from Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA