B lymphocytes are responsible for antibody production, and therefore, are essential cells in the adaptive response to pathogens or vaccines. Even though fish are from evolutionary point of view the first animal group with adaptive immunity, and thus with B lymphocytes, there are many differences between the adaptive systems of mammals and fish and consequently in B cells from both groups. Hence, in the past years, our group has been focused in studying these differences, highlighting that B lymphocytes in fish are functionally and phenotypically more similar to mammalian B1 lymphocytes than to mammalian conventional B cells. In mammals, B1 lymphocytes are considered elements of the innate immune system, being responsible for the fast production of innate IgMs that can limit pathogen dissemination while a specific B cell response is mounted. Of course, this resemblance of fish B cells with mammalian B1 cells have many implications as to how these cells respond to antigens.
Antigen presenting cells
Our group has been the first to describe a specific lineage of dendritic cells in fish. Through the combination of antibodies against MHC II and CD8, we defined a cell population with dendritic cell characteristics. We have identified these cells in skin, gills and intestine, phenotypically and functionally characterizing the cells in each case. Our studies point to these cells as a common ancient ancestor of different mammalian dendritic cell lineages with cross-presenting capacities.
In the past years, we have studied the effects of different cytokines on fish B cells, including BAFF, APRIL, BALM IL2, IL4, IL10 and IL21 among others. We have determined the effects of these cytokines on the survival of fish B cells, their proliferative capacity, their phagocytic capacity, as well as their differentiation to plasma cells.
Vaccines and treatments
To date, most commercial vaccines for use in aquaculture are vaccines against bacterial pathogens that require an intraperitoneal injection. In contrast, the few vaccines available in the market against viruses are not very effective and there are no commercial vaccines against parasites. Therefore, part of the group efforts are focused on the design of new viral vaccine antigens, as well as on the search of effective molecular adjuvants that can increase the immunogenicity of these antigens. We have a special interest in the design of oral vaccines/adjuvants as the oral administration route would be the most interesting for the aquaculture sector, avoiding taking the fish out of the water with the stress in the fish and the workload to the fish farmer that this implies.
Additionally, we also study the effects of different diet immunostimulants that can increase the immune status of the fish, rendering them more resistant to pathogens.