Phagocytic and Bactericidal Properties of Channel Catfish Peritoneal Macrophages Exposed to Edwardsiella ictaluri Live Attenuated Vaccine and Wild-Type Strains

Abstract

Edwardsiella ictaluri (E. ictaluri), a Gram-negative, intracellular, facultative bacterium, is the causative agent of enteric septicemia of catfish (ESC), which is one of the most significant diseases of farmed channel catfish. Macrophages have a critical role in major defense mechanisms against bacterial infections by migrating to the site of infection, engulfing and killing pathogens, and priming adaptive immune responses. Vaccination of catfish with E. ictaluri live attenuated vaccine (LAV) strains increased the efficiency of phagocytosis and bacterial killing in catfish peritoneal macrophages compared in vitro with macrophages from non-vaccinated fish. Recently, our group developed several protective LAV strains from E. ictaluri. However, their effects on the antigen uptake and bacterial killing in catfish macrophages have not been evaluated. In this study, we assessed the phagocytic and bactericidal activity of peritoneal macrophages in the uptake of E. ictaluri wild-type (WT) and two LAV strains. We found that phagocytosis of LAV strains was significantly higher compared to their WT counterpart in peritoneal macrophages. Moreover, the uptake of E. ictaluri opsonized with sera from vaccinated catfish was more efficient than when opsonized with sera from sham-vaccinated fish. Notably, catfish macrophages did not lose their phagocytic properties at 4°C, as described previously in mammalian and zebrafish models. Also, opsonization of E. ictaluri with inactivated sera from vaccinated and sham-vaccinated catfish decreased significantly phagocytic uptake of bacteria at 32°C, and virtually suppressed endocytosis at 4°C, suggesting the important role of complement-dependent mechanisms in catfish macrophage phagocytosis. In conclusion, our data on enhanced phagocytic capacity and effective killing ability in macrophages of vaccine strains suggested the LAVs’ advantage if processed and presented in the form of peptides to specific lymphocytes of an adaptive immune system and emphasize the importance of macrophage-mediated immunity against ESC. Furthermore, we showed the role of complement-dependent mechanisms in the phagocytic uptakes of E. ictaluri in catfish peritoneal macrophages at 4 and 32°C. Finally, LAV vaccine-induced bacterial phagocytosis and killing properties of peritoneal macrophages emphasized the importance of the innate immune responses in ESC.

Haemato-immunological responses and effectiveness of feed-based bivalent vaccine against Streptococcus iniae and Aeromonas hydrophila infections in hybrid red tilapia (Oreochromis mossambicus × O. niloticus)

“…The phagocytic cells are functioned in stimulating an inflammatory response, phagocytosis and bactericidal action and nitric oxide (NO) for killed pathogens. In the current study, the phagocytosis activity in vaccinated fish was higher both before and after infection with S. iniae and A. hydrophila compared with the unvaccinated fish, which was similar to record by Kordon [51]. Additionally, similar results have been also shown in vaccinated striped catfish (Pangasianodon hypophthalmus) those were immunised with A. hydrophila [49].…”

Edwardsiella ictaluri evpP is required for colonisation of channel catfish ovary cells and necrosis in anterior kidney macrophages

“…We previously reported that deletion of evpB of T6SS caused nearly complete loss of E. ictaluri virulence in catfish and EievpB provided good protection against EiWT infection (Abdelhamed, Lawrence, & Karsi, 2018). EievpB also showed high-internalisation rate in catfish peritoneal macrophages (Kordon et al, 2018). In this study, removal of evpP caused numerical but not statistically significant virulence attenuation in catfish, and the internalisation rate of EiΔevpP in catfish peritoneal macrophages was similar to that of EiWT.…”

“…Bacterial killing and cytospin were performed as previously described (Booth, Beekman, & Thune, 2009;Kordon et al, 2018;Russo, Shoemaker, Panangala, & Klesius, 2009 Peritoneal macrophages were incubated with EiΔevpP and EiWT at 32°C for 2 hr. Then, cells were harvested and washed, and the cytospin slides were prepared by using a Cyto-Tek cytocentrifuge (Sakura) set at 160 g (500 rpm) for 1 min.…”

“…Then, cells were harvested and washed, and the cytospin slides were prepared by using a Cyto-Tek cytocentrifuge (Sakura) set at 160 g (500 rpm) for 1 min. Samples were fixed and stained with Wright's stain (Merck; Kordon et al, 2018). Samples were analysed with an Olympus BX60 microscope (Olympus U-TV1 X) and pictured by using Infinity software (Lumenera Corporation).…”

Zinc transporter SLC39A7 relieves zinc deficiency to suppress alternative macrophage activation and impairment of phagocytosis

“…Cells were examined under fluorescence microscopy. For flow cytometry, the phagocytosis to BCG-p was performed as previously report [41]. Briefly, THP-1 cells were infected by GFP-expressing BCG-p for 4 h, then the cells were rinsed with PBS, next the cells were removed form plates and were measured with BD Accuri C6.…”