Enhancing Host Immunity: Immune Priming in Manila Clams (Ruditapes philippinarum) to Combat Perkinsus olseni

The Manila clam (Ruditapes philippinarum) is one of the most economically and ecologically important bivalve species cultivated throughout Europe and Asia. In Italy, the Venice Lagoon is one of the major clam production site that supports local communities and livelihoods. However, the sustainability of clam production is increasingly threatened by outbreaks of the protozoan parasite Perkinsus olseni. Rising temperatures caused by climate change are worsening this problem by making clams more vulnerable to infection and disturbing the fragile ecological balance of the lagoon ecosystem. This study aimed to develop an immune priming protocol for R. philippinarum and to identify the optimal priming conditions that enhance the clam’s innate immune defence. Juvenile clams were exposed, via bath exposure, to varying concentrations of inactivated P. olseni under controlled laboratory conditions, and the efficacy was evaluated by analysing transcriptional responses of six immune and stress related genes (C-type lectin, oxidative stress-induced growth inhibitor 2-like, UV excision repair protein RAD23 homolog B-like, contig_4244, HEXIM1-like, and serine/arginine-rich splicing factor 6-like) using quantitative real-time PCR. Results revealed that moderate antigen doses elicited the strongest gene activation, particularly for Contig_4244 and RAD23, which were significantly upregulated following exposure. Upon secondary challenge, Contig_4244 and Oxidative stress-induced growth inhibitor exhibited enhanced expression, suggesting a transcriptional memory consistent with immune priming. These findings provide molecular evidence supporting the potential for immune priming in bivalves and highlight the roles of oxidative stress regulation and DNA repair pathways in this process. Overall, this study establishes a baseline immune priming protocol and optimal antigen concentration for R. philippinarum, laying the groundwork for sustainable, non-chemical disease management strategies in clam aquaculture and contributing to a better understanding of innate immune plasticity in marine invertebrates.