Kinetics of pIgR and IgM immune responses in snakehead (Channa argus) to inactivated Aeromonas hydrophila via immersion and intraperitoneal injection.

This research was intended to investigate the kinetics of polymeric immunoglobulin receptor (pIgR) and its ligand immunoglobulins (Ig) in snakehead (Channa argus) through different vaccine delivery methods. First, we employed Oxford Nanopore Technologies (ONT) sequencing technology to acquire the snakehead fish's complete transcriptome, and the full coding sequence (CDS) of pIgR was identified and isolated through transcriptome sequencing named ChpIgR. The CDS sequence spanned 1251 base pairs, translating into a protein that consists of 416 amino acids and has a molecular weight of around 45.80 kDa. The ChpIgR had a pair of immunoglobulin-like domains in addition to a transmembrane region and an intracellular region. Furthermore, a polyclonal antibody targeting the snakehead recombinant ChpIgR was constructed. ChpIgR and IgM responses were analyzed after immunization with Aeromonas hydrophila. Although ChpIgR and IgM displayed a comparable transcription level, ChpIgR exhibited a more rapid increase and reached its peak earlier than IgM. Both vaccinated groups experienced an elevation in ChpIgR mRNA levels in the gill and spleen. On the other hand, the bath immersion group manifested that the skin, gills, and intestines had an elevated IgM mRNA expression, whereas the intraperitoneal vaccination group reported that the spleen and head kidney possessed a greater expression. The ELISA results indicated that the IgM and ChpIgR levels reached their highest peak more rapidly in the skin and gill mucus in the bathing group, whereas they reached a greater peak in intestinal mucus in the injection group. The outcomes indicated that both bath and intraperitoneal vaccinations increased ChpIgR and secretory Ig levels in mucus and bile, shedding light on the function of pIgR in immune response and laying the foundation for future studies on pIgR-linked immune defenses in teleosts.