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Characterization of B Cell Responses in Rainbow Trout (Oncorhynchus Mykiss) Affected by Red Mark Syndrome
J Germán Herranz-Jusdado1, Samuel Vicente-Gil2, Esther Morel2
1Skretting Aquaculture Innovation, Stavanger, 4016, Norway.
Abstract:
Red mark syndrome (RMS) is a disease affecting rainbow trout. Although the precise etiology of this disease is still under debate, a Midichloria-like organism (MLO) is suspected as the triggering agent. RMS provokes characteristic skin lesions. Previous investigations pointed to a local immune response characterized by a B cell influx. To elaborate on these findings, here, this study extensively characterizes systemic and local B cell responses in RMS-affected fish. The local influx of IgM+ B cells to the skin lesions is confirmed, and a differentiation of these B cells to plasma-like cells is demonstrated. IgM repertoires suggested a polyclonal activation of local B cells and some trafficking between skin and head kidney. Finally, the fact that transcripts of the gene coding for MLO 16S rRNA are found in sorted skin IgM+ B cells and non-IgM+ skin leukocytes reveals the capacity of this intracellular bacterium to be internalized by B cells, where it may possibly directly interfere with intracellular pathways. The data significantly advances the knowledge on RMS and provides another example of a fish pathology in which fish B cells seem pivotal, possibly because of the specific ways in which teleost B cells intrinsically sense and respond to pathogens.
Insights
Red mark syndrome (RMS) in rainbow trout involves a local immune response with B cells migrating to skin lesions and differentiating into plasma cells. This study confirms Midichloria-like organism (MLO) presence within B cells, advancing understanding of this fish disease.
Area of Science:
- Aquatic animal health
- Immunology
- Fish pathology
Background:
- Red mark syndrome (RMS) is a significant disease in rainbow trout, characterized by distinct skin lesions.
- A Midichloria-like organism (MLO) is the suspected causative agent, though its role is under investigation.
- Previous studies indicated a local immune response involving B cell infiltration in RMS lesions.
Purpose of the Study:
- To comprehensively characterize the systemic and local B cell responses in rainbow trout affected by RMS.
- To investigate the interaction between MLO and B cells within the context of RMS pathogenesis.
- To elucidate the role of B cells in the immune response to RMS.
Main Methods:
- Flow cytometry and immunohistochemistry to analyze B cell populations (IgM+ B cells) in skin lesions and head kidney.
- Analysis of IgM repertoires to assess B cell activation and clonality.
- Molecular detection of MLO 16S rRNA in sorted immune cell populations from affected fish skin.
Main Results:
- Confirmed local influx and differentiation of IgM+ B cells into plasma-like cells within RMS skin lesions.
- Demonstrated polyclonal B cell activation and suggested trafficking of B cells between skin and head kidney.
- Detected MLO 16S rRNA transcripts in sorted IgM+ B cells and other skin leukocytes, indicating MLO internalization by B cells.
Conclusions:
- Fish B cells play a pivotal role in the immune response to Red Mark Syndrome.
- The findings suggest MLO can be internalized by B cells, potentially interfering with intracellular pathways.
- This study enhances knowledge of RMS pathogenesis and highlights the unique immune sensing capabilities of teleost B cells.
