Exploring the pathogenesis of Anophryoides haemophila infection: impacts on immune responses in American lobster (Homarus americanus)

The American lobster (Homarus americanus) is a species of cultural and economic importance in eastern Canada and the northeastern United States, supporting a multi-billion-dollar commercial fishery. The ciliated protist Anophryoides haemophila threatens wild and captive lobsters as well as the sustainability of this fishery. We employed RNA sequencing (RNA-seq) to investigate expression changes in 31,803 genes of H. americanus hepatopancreas following A. haemophila challenge, revealing new insights into the lobster's immune response. RNA-seq provided much deeper and broader insights than the previous microarray study, uncovering 152 immune- and stress-related genes, including anti-lipopolysaccharide factors (ALFs), the pentraxin serum amyloid A (SAA), lectins, Toll-like receptors, peptidoglycan recognition proteins, cytokines, relish, cactus, hyperglycemic hormone, and components of coagulation and antioxidant systems. We observed that the direction and magnitude of expression for some immune-related genes differed from those reported in previous bacterial or viral pathogen challenges. However, direct comparisons across studies are constrained by differences in experimental design and sampling timepoints. These findings suggest the potential for pathogen-dependent modulation of immune responses in H. americanus, which will require direct comparative studies across pathogens and infection intensities to be fully resolved. This work sheds new light on the complexity of the crustacean immune system and provides a foundation for developing future approaches to disease research and management in aquaculture crustacean species.