Characterization of Small, Mononuclear Blood Cells from Salmon Having High Phagocytic Capacity and Ability to Differentiate into Dendritic like Cells

Abstract

Phagocytes are the principal component of the innate immune system, playing a key role in the clearance of foreign particles that include potential pathogens. In vertebrates, both neutrophils and mononuclear cells like monocytes, macrophages and dendritic cells are all professional phagocytes. In teleosts, B-lymphocytes also have potent phagocytic ability. We have isolated a population of small (<5 µm), mononuclear blood cells from Atlantic salmon (Salmo salar L.) not previously characterized. In order to identify them, we have performed morphological, gene expression, flow cytometry, cytochemical, ultrastructural and functional analyses. Interestingly, they highly express the gene encoding CD83, the most characteristic cell surface marker for dendritic cells in mammals, and MHC class II limited to professional antigen presenting cells. They did not express genes nor did they have cell markers for B-cells, T-cells, monocytes/macrophages or neutrophils as shown by qRT-PCR, flow cytometry and immunoblotting. A remarkable feature of these cells is their potent phagocytic capacity. Their oxygen-independent killing mechanism, as shown by intense acid phosphatase staining, is supported by lack of respiratory burst and myeloperoxidase activity and the acid phosphatase's sensitivity to tartrate. They show a high level of morphological plasticity, as, upon stimulation with mitogens, they change morphology and obtain branching protrusions similarly to dendritic cells. We suggest, based on our findings, that the small, round cells described here are progenitor cells with potential to differentiate into dendritic like cells, although we can not exclude the possibility that they represent a novel cell type.

Functional characterization of IgM+ B cells and adaptive immunity in lumpfish (Cyclopterus lumpus L.)

“…These small mononuclear cells, which had ingested numerous beads, were easily observed in flow cytometry analysis and colorrapid staining of phagocytic cells from PBL. The nature of these cells is currently not known, but similar cells have been reported from trout (Li et al, 2006), Atlantic salmon (Haugland et al, 2012b) and wrasse (Haugland et al, 2014). We have earlier suggested for salmon and wrasse that these cells may be precursor cells or immature cells (Haugland et al, 2012a(Haugland et al, , 2014.…”

Insight from Molecular, Pathological, and Immunohistochemical Studies on Cellular and Humoral Mechanisms Responsible for Vaccine-Induced Protection of Rainbow Trout against Yersinia ruckeri

“…ruckeri serum antibody reactivity was determined by enzyme-linked immunosorbent assay (ELISA) as recently described (25). Dilution series of fish sera (1,10 Ϫ1 , . .…”

“…Classical histopathological studies in fish exposed to bacteria, including Y. ruckeri, have placed their focus on pathogenesis in various tissues and organs without addressing the differential and sequential immune cell involvement and dynamics in central lymphoid organs (7,8). Considering the scarcity of flow cytometric assays in vaccinated fish (9)(10)(11), due to a lack of immunological reagents (monoclonal antibodies reacting with native cell markers) (12)(13)(14)(15)(16), we were encouraged to undertake descriptions of the morphopathological alterations/modifications of immune organs following challenge. This approach would suggest specific cell types as being active during the development of immunity toward ERM.…”

Identification and expression modulation of a C-type lectin domain family 4 homologue that is highly expressed in monocytes/macrophages in rainbow trout (Oncorhynchus mykiss)

“…Two recent studies also confirm the presence of antigen presenting cells in Atlantic salmon (Salmo salar). Lagos et al (2012) showed that antigen presenting cells can be induced by CD40L stimulation and Haugland et al (2012) identified a small population of salmon blood leukocytes/putative DC progenitors, with a potent phagocytic capacity by magnetic bead depletion, using the monoclonal antibody C4B6 (reactive with salmon leukocytes) to fractionate peripheral blood leukocytes. In the present study we describe the identification and expression analysis of a CLEC4-like molecule from rainbow trout (termed CLEC4T1) to aid identification of antigen presenting cells in salmonids.…”