The Acute Immune Responses of the Common Carp Cyprinus carpio to PLGA Microparticles-The Interactions of a Teleost Fish with a Foreign Material.

Poly lactic-co-glycolic acid (PLGA) particles safely and effectively deliver pharmaceutical ingredients, with many applications approved for clinical use in humans. In fishes, PLGA particles are being considered as carriers of therapeutic drugs and vaccine antigens. However, existing studies focus mainly on vaccine antigens, the endpoint immune responses to these (e.g., improved antibody titres), without deeper understanding of whether fishes react to the carrier. To test whether or not PLGA are recognized by or interact at all with the immune system of a teleost fish, we prepared, characterized and injected PLGA microparticles intraperitoneally into common carp. The influx, phenotype of inflammatory leukocytes, and their capacity to produce reactive oxygen species and phagocytose PLGA microparticles were tested by flow cytometry, qPCR, and microscopy. PLGA microparticles were indeed recognized. However, they induced only transient recruitment of inflammatory leukocytes that was resolved 4 days later whereas only the smallest µm-sized particles were phagocytosed. The overall response resembled that described in mammals against foreign materials. Given the similarities between our findings and those described in mammals, PLGA particles can be adapted to play a dual role as both antigen and drug carriers in fishes, depending on the administered dose and their design.

Variations in Rainbow Trout Immune Responses against A. salmonicida: Evidence of an Internal Seasonal Clock in Oncorhynchus mykiss.

In poikilothermic vertebrates, seasonality influences different immunological parameters such as leukocyte numbers, phagocytic activity, and antibody titers. This phenomenon has been described in different teleost species, with immunological parameters peaking during warmer months and decreased levels during winter. In this study, the cellular immune responses of rainbow trout (Oncorhynchus mykiss) kept under constant photoperiod and water temperature against intraperitoneally injected Aeromonas salmonicida during the summer and winter were investigated. The kinetics of different leukocyte subpopulations from peritoneal cavity, spleen, and head kidney in response to the bacteria was measured by flow cytometry. Furthermore, the kinetics of induced A. salmonicida-specific antibodies was evaluated by ELISA. Despite maintaining the photoperiod and water temperature as constant, different cell baselines were detected in all organs analyzed. During the winter months, B- and T-cell responses were decreased, contrary to what was observed during summer months. However, the specific antibody titers were similar between the two seasons. Natural antibodies, however, were greatly increased 12 h post-injection only during the wintertime. Altogether, our results suggest a bias toward innate immune responses and potential lymphoid immunosuppression in the wintertime in trout. These seasonal differences, despite photoperiod and water temperature being kept constant, suggest an internal inter-seasonal or circannual clock controlling the immune system and physiology of this teleost fish.

Method for Isolation of Myxozoan Proliferative Stages from Fish at High Yield and Purity: An Essential Prerequisite for In Vitro, In Vivo and Genomics-Based Research Developments.

Myxozoans are a diverse group of microscopic cnidarian parasites and some representatives are associated with important diseases in fish, in both marine and freshwater aquaculture systems. Research on myxozoans has been largely hampered by the inability to isolate myxozoan parasites from their host tissues. In this study, we developed and optimized a method to isolate the myxozoan proliferative stages of different size and cellularity from fish blood, using DEAE-cellulose ion exchange chromatography. We optimized several parameters and obtained 99-100% parasite purity, as well as high survival and infectivity. Using polyclonal pan-carp blood cell-specific antibodies, we further developed a rapid cytometric assay for quantification of the proliferative stages, not only in highly concentrated DEAE-C isolates but also in dilute conditions in full blood. Early developmental stages of myxozoans are key to parasite proliferation, establishment, and pathology in their hosts. The isolation of these stages not only opens new possibilities for in vivo and in vitro studies, but also for obtaining purified DNA and protein extracts for downstream analyses. Hence, we provide a long-desired tool that will advance the functional research into the mechanisms of host exploitation and immune stimulation/evasion in this group, which could contribute greatly to the development of therapeutic strategies against myxozoans.

Identification of human plasma cells with a lamprey monoclonal antibody.

Ab-producing plasma cells (PCs) serve as key participants in countering pathogenic challenges as well as being contributors to autoimmune and malignant disorders. Thus far, only a limited number of PC-specific markers have been identified. The characterization of the unique variable lymphocyte receptor (VLR) Abs that are made by evolutionarily distant jawless vertebrates prompted us to investigate whether VLR Abs could detect novel PC antigens that have not been recognized by conventional Abs. Here, we describe a monoclonal lamprey Ab, VLRB MM3, that was raised against primary multiple myeloma cells. VLRB MM3 recognizes a unique epitope of the CD38 ectoenzyme that is present on plasmablasts and PCs from healthy individuals and on most, but not all, multiple myelomas. Binding by the VLRB MM3 Ab coincides with CD38 dimerization and NAD glycohydrolase activity. Our data demonstrate that the lamprey VLRB MM3 Ab is a unique reagent for the identification of plasmablasts and PCs, with potential applications in the diagnosis and therapeutic intervention of PC or autoimmune disorders.