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.
Highlights
Interleukin (IL)-22 was originally identified as an IL-10-related T cell-derived inducible factor in 2000 (Dumoutier et al, 2000)
MAb L8 reacted with peptide L8 and rIL-22 but not peptide L7 and rIFN-γ (Fig. S3), indicating that both monoclonal antibodies (mAbs) can react with trout rIL-22 in ELISA
IL-22 appears to have a similar biological function to mammals, and can modulate antimicrobial peptide (AMP) expression suggesting a potent role in triggering antimicrobial defences for microbial clearance (Monte et al, 2011)
Summary
Interleukin (IL)-22 was originally identified as an IL-10-related T cell-derived inducible factor in 2000 (Dumoutier et al, 2000). It is a member of the IL-10 family that in mammals includes IL-10, IL-19, IL20, IL-24, and IL-26, in addition to IL-22 (Dudakov et al, 2015). IL-10 family cytokines are produced by both innate and adaptive immune cells, and exert essential functions to maintain tissue homeostasis during infection and inflammation (Ouyang and O'Garra, 2019). Myeloid cells such as macrophages, neutrophils and mast cells, as well as non-hematopoietic fibroblasts have been reported to have the ability to produce IL-22 in different disease models (Lanfranca et al, 2016)
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