Litopenaeus vannamei heat shock protein 10 is a novel immune regulator that enhances shrimp defense against Ecytonucleospora hepatopenaei infection through LvSPL3-mediated prophenoloxidase activation.

Small heat shock proteins (sHSPs) are ATP-independent chaperones synthesized by cells in response to various stresses, including pathogen infection, to maintain cellular and protein homeostasis. However, their roles in shrimp innate immunity remain largely unknown. Here, we demonstrate that LvHSP10 is a key immune regulator in Litopenaeus vannamei during infection with the microsporidian Ecytonucleospora hepatopenaei (EHP). LvHSP10 expression in both hemocytes and hepatopancreas was markedly induced following EHP infection, with a >20-fold increase in hemocytes at 7 days post-cohabitation (dpc). Immunofluorescence analysis further revealed that LvHSP10 was localized in hyaline and semi-granular hemocytes, with its expression increasing after EHP infection. Administration of recombinant LvHSP10 significantly reduced the EHP loads and enhanced the expression of immune-related genes involved in the Toll, JAK/STAT, IMD, antimicrobial peptide (AMP), prophenoloxidase (proPO), apoptosis, and stress-response pathways. Pull-down assays and co-immunoprecipitation identified a serine protease-like protein 3 (LvSPL3) as an LvHSP10-interacting partner. Furthermore, co-incubation of recombinant LvHSP10 and LvSPL3 markedly enhanced phenoloxidase (PO) activity, suggesting that LvHSP10 promotes proPO activation through its interaction with LvSPL3. Collectively, these findings identify LvHSP10 as an immune regulator that enhances shrimp defense against EHP infection by coordinating multiple immune signaling pathways and activating the proPO system through LvSPL3.