The deep-sea mytilid mussel, Bathymodiolus japonicus, harbors methane-oxidizing bacteria in the gill epithelial cells that are transmitted horizontally or environmentally to the next generation of the mussel. It remains to be elucidated how the symbiotic bacteria are maintained under the immune defense system of the host mussels. As hemocytes generally play a major role in the immune system, their characterization is important in understanding the immune defense system of the symbiotic mussel. In hemocytes of B. japonicus, two types of granulocytes and one type of agranulocyte have been reported. To develop biomarkers to identify these hemocyte subpopulations, we generated a monoclonal antibody (mAb) library against mussel hemocytes. We obtained 16 hybridoma clones producing mAbs against the hemocytes. These were divided into six categories based on reactivity to the hemocyte subpopulations. Ten out of 16 mAbs reacted to all of the hemocytes. Four of the remaining six mAbs respectively and exclusively reacted to granulocytes, agranulocytes, a subset of granulocytes, and a subset of agranulocytes. Two of them recognized both granulocytes and agranulocytes but only their subsets. These suggested that granulocytes and agranulocytes are respectively composed of hetetogeneous subsets. The present mAb library may be useful not only for the classification of the hemocytes, but also for investigating their functions, differentiation and localizations in the body. The information obtained from the mAbs will be a baseline for understanding the relationship between the immunological defense system and stable maintenance of symbiotic bacteria in the deep-sea symbiotic bivalves.
2016 Japan Agency for Marine-Earth Science and Technology