PIgR and Ig responses in largemouth bass (Micropterus salmoides) following intraperitoneal injection and bath immunization with inactivated Aeromonas hydrophila

The immunoglobulins (Ig) and polymeric immunoglobulin receptor (pIgR) are crucial in protecting organisms against pathogen invasion. However, further clarification regarding their mucosal immune responses is required, particularly when considering various vaccine administration routes. Herein, polyclonal antibodies against largemouth bass (Micropterus salmoides) recombinant pIgR and IgM were prepared, respectively. Moreover, pIgR and IgM response features were investigated after immunization via bath and intraperitoneal injection with Aeromonas hydrophila. The findings indicated that the pIgR transcription level was comparable to that of IgM in the skin, gills, intestine, liver, spleen, and head kidney. Nonetheless, pIgR increased at a quicker rate and peaked earlier than IgM. The pIgR was overexpressed in the skin in the bath immersion group and the spleen in the intraperitoneal immunization group. Meanwhile, IgM expression levels exhibited higher results in the skin and gills in the bath immersion group as well as the liver and spleen in the intraperitoneal immunization group. The ELISA results demonstrated an elevation of IgM and pIgR protein concentrations in the bile as well as skin, gill, and intestine mucus. The bath immersion group exhibited earlier peak levels in skin and gill mucus, whereas the intraperitoneal immunization group displayed a greater peak extent in the bile. Secretory component molecules (SC) were found at about 37 kDa in the bile as well as skin, gill, and intestine mucus, excluding serum, which was close to the theoretical molecular mass derived from the largemouth bass pIgR sequence. The findings have revealed that both bath immunization and intraperitoneal administration vaccination could induce pIgR and IgM production in mucus and bile. Nevertheless, variations within pIgR and IgM responses were detected via various immunization pathways, providing valuable insights into teleost mucosal immunity and strategies for safeguarding against pathogen invasion.