Freeze‐Dried <i>Lactiplantibacillus plantarum</i> Regulates Formation of Extracellular Traps in <i>Penaeus vannamei</i> Ex Vivo

The formation of extracellular traps (ETosis) is an innate immune mechanism in shrimp against pathogens. Microorganisms are entrapped in extruded DNA fibres co-localised with antimicrobial peptides and eventually killed. However, as a cell death mechanism, its strict regulation is essential as excessive formation of ETs may cause detrimental effects to the host by contributing to disease pathophysiology. Here, we investigated the ability of freeze-dried Lactiplantibacillus plantarum (FD-LAB), previously reported to enhance shrimp immunity against pathogenic infections, to regulate ETosis. In an ex vivo setup, gill cells and circulating hemocytes were pre-exposed to FD-LAB and were then stimulated with Vibrio parahaemolyticus. Results showed that V. parahaemolyticus alone induced ETosis in both gill cells and circulating hemocytes, while FD-LAB alone did not. However, when cells were pre-exposed to FD-LAB prior to stimulation with V. parahaemolyticus, no ETosis occurred. Similarly, changes in reactive oxygen species (ROS) production coincided with the formation of ETs, thus signifying that FD-LAB may regulate ETosis in shrimp gill cells and circulating hemocytes possibly by dampening ROS production. These results present a novel means to regulate ETosis and indicate that FD-LAB may enhance shrimp immunity while also acting on immune regulation.