The bound fraction (C4B6+ cells) contained both polymorphonuclear (PML) and mononuclear cells (L?=?leukocytes, M?=?monocytes) while the cells in the unbound portion (C4B6? cells) were small, mononuclear cells with low level of granularity. and mononuclear cells Rabbit Polyclonal to POLR1C like monocytes, macrophages and dendritic cells are all professional phagocytes. In teleosts, B-lymphocytes also have potent phagocytic ability. We have isolated a human population of small (<5 m), mononuclear blood cells from Atlantic salmon (L.) not previously characterized. In order to determine them, we have performed morphological, gene manifestation, circulation cytometry, cytochemical, ultrastructural and functional analyses. Interestingly, they highly communicate the gene encoding CD83, the most characteristic cell surface marker for dendritic cells in mammals, and MHC class II limited to professional antigen showing cells. They did not communicate genes nor did they have cell markers for B-cells, T-cells, monocytes/macrophages or neutrophils as demonstrated by qRT-PCR, flow cytometry and immunoblotting. A remarkable feature of these cells is definitely their potent phagocytic capacity. Their oxygen-independent killing mechanism, as demonstrated by intense acidity phosphatase staining, is definitely supported by lack of respiratory burst and myeloperoxidase activity and the acid phosphatase's level of sensitivity to tartrate. They display a high level of morphological plasticity, as, upon activation with mitogens, they switch morphology and obtain branching protrusions similarly to dendritic cells. We suggest, based on our findings, that the small, round cells explained here are progenitor cells with potential to differentiate into dendritic like cells, although we can not exclude the possibility that they symbolize a novel cell type. Introduction In fish, the phagocytic defense mechanism plays a pivotal part in non-specific immunity. As known, macrophages and neutrophils have high phagocytic activity. Among the small leukocytes, fish B-cells are professional phagocytes with microbicidal capabilities [1], [2]. Phagocytosis by additional professional Chlorin E6 phagocytic cells in fish like dendritic cells (DCs) have only recently been explained [3], [4]. It has also been reported that fish thrombocytes are able to take up and destroy L.) smolts from Urke Fiskeoppdrett While, Norway, were kept in the damp lab, Bergen High-Technology center, under normal optimal rearing conditions at a temp of 8C, salinity of 34 and 24 hour light. These facilities are authorized by the Norwegian Animal Research Expert for rearing of fish. The water circulation was 1200 l per hour, and the fish was feed with commercial dry feed from Skretting, Norway. There Chlorin E6 were no indications of infection and no mortality in the fish. The fish were quickly netted and killed by a razor-sharp blow to the head. Blood samples were collected as explained below and stored on snow before further processing and fish size (cm) and excess weight (g) were recorded. Isolation of Peripheral Blood Leukocytes Peripheral blood (4C8 ml) collected from vena caudalis of Atlantic salmon (L.), 600C1050 g of excess weight, using a syringe, was transferred to Chlorin E6 heparinised containers and diluted (12) in Leibovitz L-15+ (L-15, (Cambrex) (modified to 370 mOsm by adding a solution consisting of 5% (v/v) 0.41 M NaCl, 0.33 M NaHCO3 and 0.66% (w/v) D-glucose), supplemented with 100 g/ml gentamicin sulphate (Cambrex), 2 mM L-glutamine (Cambrex) and 15 mM HEPES). Leukocytes from peripheral blood (PBL) were then isolated on discontinuous Percoll gradients as explained previously [33]. Cell number, aggregation element and viability were analyzed using a CASY cell counter (Innovatis AG). Main Antibodies The polyclonal anti-TO serum utilized for immunofluorescence analysis stain all salmon leukocytes [16]. The Mab C4B6, reacting with different subtypes of leukocytes [33], [34], were used in magnetic triggered cell sorting (MACS). Chlorin E6 For circulation cytometry analyses, different monoclonal antibodies (MAbs) were used; C4B6 (anti-leukocytes), E3D9 (anti-neutrophils), C7G7 (anti-IgM/B-cells) and G2H3 (anti-IgM/B-cells). Their specificity and reactivity are explained in [33], [34]. The MAbs 22-1, 42-1 and 8-3, reacting with trout thrombocytes [31], were a generous gift from Dr. Bernd K?llner, Friedrich-Loeffler-Institut, Germany. Also, a polyclonal Rabbit Anti-Human CD3 (DakoCytomation) was used in circulation cytometry analyses. This antibody reacts with both T-cells and Ig+ cells in salmon (personal unpublished analyses, earlier described as T-cell specific of Bakke-McKellep et al. [35]). A polyclonal anti-salmon IgM antibody (from our lab) was used in immunoblotting. Magnetic Activated Cell Sorting (MACS) of Salmon PBLs PBL were fractioned having a MACS separation system (Miltenyi Biotec) using the MAb C4B6, reactive with salmon leukocytes, and goat anti-mouse IgG Chlorin E6 Microbeads (Miltenyi Biotec). PBL were incubated with 1 ml main antibody remedy (10 g ml?1 C4B6-mouse IgG antibody in 1 PBS with 0.5% BSA per 2107 cells and maximum 3.5107 cells per LD column (Miltenyi Biotec)) for 20 min at 4C and washed once with MACS buffer (1 PBS, 0.5% BSA and 2 mM EDTA, pH 7.3). Further, the cells were incubated with goat anti-mouse IgG Microbeads for 20 min at 4C, washed.