Immunomodulatory effect of plasma-derived Streptococcus parauberis challenged olive flounder (Paralichthys olivaceus) exosomes against Streptococcus parauberis.

Abstract

This study investigates the transcriptomic and immunomodulatory effects of exosomes derived from Streptococcus parauberis-infected olive flounder (Paralichthys olivaceus) plasma (Sp-Exo) and their potential role in conferring disease resistance. RNA sequencing of kidneys in Sp-Exo treated olive flounder identified 21,581 genes, with 1182 showing substantial differential expression. Functional annotation revealed enrichment of immune-related pathways such as focal adhesion, PI3K-Akt, and MAPK signaling among upregulated genes, while downregulated genes were associated with cardiomyopathy-related pathways. To evaluate the immunomodulatory effects of Sp-Exo, olive flounders were intraperitoneally injected with PBS (control), Sp-Exo or PBS-Exo, followed by a challenge with S. parauberis (4.2 × 10 CFU/fish). Subsequently, qRT-PCR analysis of kidney tissues at 4 days post-challenge (dpc) revealed upregulation (>1.5-fold) of immune-related genes (TLR5a, IL1β, TNFα, and IL8) in the Sp-Exo group as compared to the controls. Furthermore, Sp-Exo treatment protected 50 % (RPS: 50 %) of the fish compared to control groups. Histopathological analysis demonstrated a reduced structural damage and inflammatory lesions in Sp-Exo-treated fish, supporting its role as a protective agent. These findings highlighted the immunomodulatory properties of Sp-Exo and its potential as a vaccine candidate for managing S. parauberis infections in olive flounder. Further elucidating of Sp-Exo internalization mechanisms in host cells could provide valuable insights into host-pathogen interactions and thereby support the development of novel prophylactic strategies for aquaculture.