Induction of IL-22 protein and IL-22-producing cells in rainbow trout Oncorhynchus mykiss

Abstract

IL-22 is a critical cytokine which is involved in modulating tissue responses during inflammation, and is produced mainly by T cells and innate leucocytes. In mammals, IL-22 is a key component in mucosal defences, tissue repair, epithelial cell survival and proliferation. In teleosts, IL-22 has been cloned and studied in several species, and the transcript is highly expressed in mucosal tissues and induced by pathogen associated molecular patterns (PAMPs), suggesting IL-22 also functions as an important component of the innate immune response in fish. To investigate these immune responses further, we have validated and characterised two monoclonal antibodies (mAbs) which were raised against two different peptide immunogens of salmonid IL-22. Our results show that both mAbs specifically react to their own peptide immunogens and recombinant IL-22, and are able to detect the induction of native protein expression after stimulation. In flow cytometry, an increase in IL-22 positive cells was detected after stimulation in vitro with cytokines and PAMPs and in vivo after bacterial challenge. The immunohistochemistry results showed that IL-22 is highly upregulated in the gills after challenge, both in cells within the gill filaments and in the interbranchial lymphoid tissue. Such results suggest IL-22 may have a role in triggering local antimicrobial defences in fish that may facilitate efficient microbial clearance. Hence monitoring IL-22 producing cells/protein secretion may provide an alternative mean to assess the effectiveness of mucosal vaccines.

The Atlantic Salmon Gill Transcriptome Response in a Natural Outbreak of Salmon Gill Pox Virus Infection Reveals New Biomarkers of Gill Pathology and Suppression of Mucosal Defense

“…Interestingly, the suppression is observed during early infection, suggesting that this could be a virus-regulated effect. This inhibitory effect contrasts previous findings in rainbow trout gills after infection with A. salmonicidae, where IL-22 was strongly upregulated (47). In that study, the infection was shown to increase the number of IL-22 producing cells in the gill epithelium and interbranchial lymphoid tissue (47).…”

“…This inhibitory effect contrasts previous findings in rainbow trout gills after infection with A. salmonicidae, where IL-22 was strongly upregulated (47). In that study, the infection was shown to increase the number of IL-22 producing cells in the gill epithelium and interbranchial lymphoid tissue (47). IL-22 is expressed by innate T-cells (γδ T cells), abundant in mucosal tissue (48).…”

Characterization of IL-22 Bioactivity and IL-22-Positive Cells in Grass Carp Ctenopharyngodon idella

“…IL-22 was constitutively expressed in most tissues with immune-related functions in healthy grass carp but was more highly expressed in the gills and hindgut (Figure 2). This observation is consistent with previous studies in which basal transcription was higher in mucosal tissues such as in the gills, pyloric cecae, and the intestine (12,14,17,20,23). These studies have suggested that IL-22 may mediate inflammation and facilitate the maintenance of homeostasis of the mucosal barrier in order to provide protection against pathogens.…”

“…Further, it was found that IL-22 was markedly upregulated at mucosal sites in fish infected with gram-negative or gram-positive bacterial pathogens (15). Recently, IL-22-producing cells were characterized in rainbow trout (Oncorhynchus mykiss) and were found to reside in gill filaments and interbranchial lymphoid tissues, having accumulated thereafter the fish infected with Aeromonas salmonicida (20). That study demonstrated that IL-22 is a key regulator, which coordinates the immune responses against bacterial pathogens (20).…”

“…Recently, IL-22-producing cells were characterized in rainbow trout (Oncorhynchus mykiss) and were found to reside in gill filaments and interbranchial lymphoid tissues, having accumulated thereafter the fish infected with Aeromonas salmonicida (20). That study demonstrated that IL-22 is a key regulator, which coordinates the immune responses against bacterial pathogens (20). IL-22 bioactivity has been examined in several fish species, including Mandarin fish (17), pufferfish (21), zebrafish (13), rainbow trout (12), So-iuy mullet (Liza haematocheila) (22), turbot (Scophthalmus maximus) (14), Atlantic cod (Gadus morhua), and haddock (23).…”