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Various types of professional immune cells first emerge in fish and likely represent the primordial form and functions. Recent advancements revealed the direct connection between the central nervous system and the immune system in the mammalian brain. However, the specifics of brain-immune networks in the fish and the underlying mechanisms of teleost's brain against pathogen infection have not been fully elucidated. In this study, we investigated the distribution of markers representing cerebral cells associated with protection and professional lymphocytes in the seven major components of the Nile tilapia brain through RNA-Seq assay and observed the most dominant abundance in the medulla oblongata. The subsequent challenge test revealed the non-specific cytotoxic cells (NCCs) exhibited the strongest response against streptococcal infection of the brain. The presence of NCCs in the brain was then confirmed using immunofluorescence and the cytotoxic effects usually induced by NCCs under infection were determined as well. Collectively, these findings contribute significantly to comprehending the mechanism of fish neuroimmune interaction and enhancing our understanding of its evolutionary development., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Hou and Li.)

Imaging flow cytometry (IFC) is a powerful tool which combines flow cytometry with digital microscopy to generate quantitative high-throughput imaging data. Despite various advantages of IFC over standard flow cytometry, widespread adoption of this technology for studies in aquatic sciences is limited, probably due to the relatively high equipment cost, complexity of image analysis-based data interpretation and lack of core facilities with trained personnel. Here, we describe the application of IFC to examine phagocytosis of particles including microplastics by cells from aquatic animals. For this purpose, we studied (1) live/dead cell assays and identification of cell types, (2) phagocytosis of degradable and non-degradable particles by Atlantic salmon head kidney cells and (3) the effect of incubation temperature on phagocytosis of degradable particles in three aquatic animals-Atlantic salmon, Nile tilapia, and blue mussel. The usefulness of the developed method was assessed by evaluating the effect of incubation temperature on phagocytosis. Our studies demonstrate that IFC provides significant benefits over standard flow cytometry in phagocytosis measurement by allowing integration of morphometric parameters, especially while identifying cell populations and distinguishing between different types of fluorescent particles and detecting their localization., (Copyright © 2020 Park, Abihssira-García, Thalmann, Wiegertjes, Barreda, Olsvik and Kiron.)

Teleost B cells have phagocytic activities for ingesting particulate antigens, such as bacteria, in addition to the functional secretion of immunoglobulins (Igs). In the present study, the phagocytic activities of IgM + B cells under various differentiational conditions residing in peripheral blood leukocytes were investigated in a teleost fish Nile tilapia ( Oreochromis niloticus ). The IgM + B cells were recognized as IgM lo or IgM hi subsets based on their membrane IgM (mIgM) levels. The mIgM, secreted IgM (sIgM), major histocompatibility complex class II and reactive oxygen species were detected. Expressions of transcription factors (Pax5 and Blimp-1) and B cell signaling molecules (CD79a, CD79b, BLNK, and LYN) suggested that IgM lo B cells were resembling as plasma-like cells and IgM hi resembling as naïve/mature B cells, respectively. Analysis of phagocytic activities demonstrated that both IgM lo and IgM hi B cells have a similar phagocytic ability (phagocytosis percentage); however, the phagocytic capacity [phagocytic index and the mean fluorescence intensity (MFI)] of IgM hi B cells was significantly higher than that of IgM lo B cells. Taken together, the results indicated that B cell differentiation may cause the decrease of phagocytic capacity but not phagocytic ability of phagocytic IgM + B cells in teleost. The finding may provide an evolutionary evidence for understanding the greater specialization of the B cell in more sophisticated adaptive humoral immunity, by decreasing phagocytic activity in order to contribute its function more specifically into antibody-secreting., (Copyright © 2019 Wu, Kong, Yang, Bian, Wu, Li, Yin, Mu, Li and Ye.)