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Published in Fish & shellfish immunology on June 25, 2026.

Clam immune cells reveal specialized defense strategies against bacterial infection

Classification of hemocyte subpopulations in the clam Meretrix Petechialis and their differential immune-associated responses to Vibrio infection.

Fish & shellfish immunology • June 25, 2026 • Moderately Relevant

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AI Summary

This research paper investigates the immune responses of hemocytes (blood cells) in the clam Meretrix petechialis when exposed to Vibrio parahaemolyticus infection. The researchers identified three distinct hemocyte subpopulations with specialized immune functions: granulocytes, semi-granulocytes, and hyalinocytes. Each cell type demonstrated different defensive capabilities, with granulocytes serving as the primary phagocytes (cells that engulf pathogens) and semi-granulocytes producing high levels of lysosomes, reactive oxygen species (ROS), and nitric oxide (NO)—all critical chemical defenses against bacterial infection.

Following bacterial infection, the study revealed significant changes in immune activity over time, with total hemocyte counts peaking at 3 days post-infection and declining by day 10. Early immune responses showed heightened phagocytosis, apoptosis (programmed cell death), lysosomal activity, and ROS production, indicating that hemocytes mount an aggressive early defense strategy. The researchers discovered important correlations between immune markers: apoptosis levels correlated positively with hemocyte counts and lysosomal content, while phagocytic activity was closely linked to ROS and NO production.

The study's most significant contribution is the proposal that apoptosis rates and phagocytic activity could serve as biomarkers for assessing clam health status in aquaculture settings. This finding has practical implications for the shellfish farming industry, offering a scientific foundation for monitoring disease resistance and overall immune competence in commercially important bivalve species.

📄 Original Abstract

Vibrio infection severely threatens the sustainability of the clam aquaculture industry. As the primary defenders in bivalve mollusks, hemocytes are crucial for immunity, yet their subpopulations and functional specialization are not fully investigated. In the present study, we classified clam hemocytes in Meretrix petechialis and investigated their immune responses under Vibrio parahaemolyticus infection. Three major types of hemocytes were identified in the hemolymph, which we termed as granulocyte, semi-granulocyte and hyalinocyte. After V. parahaemolyticus infection, total hemocyte counts (THC) significantly increased at 3 days post infection (dpi), while decreased significantly at 10 dpi. Hemocytes exhibited high levels of phagocytosis, apoptosis, lysosomal, and ROS in early stages after infection (1 dpi and 3dpi), and showed low production of NO, suggesting hemocytes actively initiate immune defense. We found that granulocytes were the main phagocytes, while semi-granulocytes were the main producers of lysosomes, ROS, and NO. A significant positive correlation was revealed between apoptosis and THC as well as lysosome content, while phagocytosis was primarily correlated to ROS and NO levels. Accordingly, apoptosis and phagocytic activity may represent candidate parameters for assessing the clam's health status. In conclusion, our results provide descriptive evidence for differential immune-associated responses among hemocyte subpopulations and offer a preliminary basis for health assessment in bivalves.

Paper Type

📄 Research

Publication

Journal: Fish & shellfish immunology
Published: June 25, 2026
PMID: 42349700
DOI: 10.1016/j.fsi.2026.111541

Authors (4)

Jing Tian Key Laboratory of Tropical and Subtropical Fishery Resource Application and Cultivation, Pearl River Fisheries Research Institute, Chinese Academy of Fisheries Sciences, Guangzhou 510380, China; State Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266000, China. Electronic address: zjtianjing@prfri.ac.cn.
Hongxia Wang State Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266000, China; University of Chinese Academy of Sciences, Beijing, China.
Pin Huan State Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266000, China; University of Chinese Academy of Sciences, Beijing, China. Electronic address: huanpin@qdio.ac.cn.
Baozhong Liu State Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266000, China; University of Chinese Academy of Sciences, Beijing, China.