title: IL-25 improves IgA levels during parenteral nutrition through the JAK-STAT pathway.
abstract: BACKGROUND
  Parenteral nutrition (PN) impairs mucosal immunity and increases the risk of infection in part via lower IgA levels at mucosal surfaces. Transport of immunoglobulin A (IgA) across the mucosa to the gut lumen depends on the epithelial transport protein, polymeric immunoglobulin receptor (pIgR), which is reduced during PN. In vitro, studies demonstrate that IL-4 up-regulates pIgR production via Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling. Because IL-4 stimulates IgA and is reduced during PN, we hypothesized that the suppressed pIgR is a result of decreased JAK-1 and STAT-6 phosphorylation. Because IL-4 is mediated by IL-25, we also hypothesized that PN + IL-25 would restore luminal IgA by increasing phosphorylated JAK-1 and STAT-6, resulting in increased tissue pIgR and luminal IgA.
  
  
  METHODS
  Experiment 1: 2 days after intravenous cannulation, male Institute of Cancer Research mice were randomized to chow (n = 11) or PN (n = 9). Experiment 2: 2 days after intravenous cannulation, male Institute of Cancer Research mice were randomized to chow (n = 12), PN (n = 10), or PN + 0.7 μg of exogenous IL-25 (n = 11) per day. After 5 days, distal ileum tissue was collected, homogenized, and protein extracted for JAK-STAT expression levels using a phospho-specific antibody microarray. Tissue was homogenized to measure pIgR expression via Western blot or fixed in 4% paraformaldehyde to measure pIgR expression via immunohistochemistry. Small intestinal wash fluid was collected and IgA was quantified using enzyme-linked immunosorbent assay.
  
  
  RESULTS
  Experiment 1: PN significantly reduced phosphorylated JAK-1 and STAT-6 compared with chow. PN also decreased the tissue levels of the Th2 cytokines, IL-4 and IL-13, as well as pIgR, and luminal IgA compared with chow. Experiment 2: Exogenous administration of PN + IL-25 increased the phosphorylated JAK-1 and STAT-6 compared with PN alone. IL-25 completely restored expression of IL-13 to chow levels. IL-4, pIgR, IgA, and phosphorylated JAK-1 were significantly increased with IL-25 treatment compared with PN but failed to reach levels measured in chow. STAT-6 was significantly increased with IL-25 treatment compared with chow and PN.
  
  
  CONCLUSIONS
  PN significantly decreases the JAK-STAT pathway by reducing levels of phosphorylated STAT-6 and JAK-1. Consistent with our previous work, sIgA, pIgR, and IL-4 decreased with PN, whereas the addition of IL-25 to PN reversed these decreases and demonstrated the role of the JAK-STAT pathway in vivo during PN.
authors.affiliation: *Department of Surgery, University of Wisconsin-Madison School of Medicine and Public Health; and †Veteran Administration Surgical Service, William S. Middleton Memorial Veterans Hospital, Madison, WI.
authors.forename: Aaron F
authors.initials: AF
authors.lastname: Heneghan
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Pierre
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Kudsk
mesh_terms: D000818:Animals; D007070:Immunoglobulin A / Q000032:analysis*; D020381:Interleukin-17 / Q000627:therapeutic use*; D053612:Janus Kinases / Q000502:physiology*; D051379:Mice; D010288:Parenteral Nutrition; D050791:STAT Transcription Factors / Q000502:physiology*; D015398:Signal Transduction
chemical_list: C486701:IL25 protein, human; D007070:Immunoglobulin A; D020381:Interleukin-17; D050791:STAT Transcription Factors; D053612:Janus Kinases