IL-33 shifts macrophage polarization, promoting resistance against Pseudomonas aeruginosa keratitis.
OBJECTIVE
To determine the role of IL-33 in resistance to Pseudomonas aeruginosa keratitis.


METHODS
Corneal IL-33 mRNA and protein levels were tested in susceptible C57BL/6 (B6) and resistant BALB/c mice. B6 mice were injected with recombinant mouse IL-33 (rmIL-33) and disease severity, bacterial load, polymorphonuclear neutrophils (PMN) infiltrate, gene expression of inflammatory, and T-helper (Th)1/Th2 cytokines were tested by RT-PCR. IL-33 signaling and macrophage (Mvarphi) polarization also were examined.


RESULTS
IL-33 mRNA and protein were expressed constitutively in the normal corneas of both groups and were significantly elevated at 1 to 5 days after infection in BALB/c over B6 mice. rmIL-33-treated B6 mice showed less severe disease than did PBS controls and exhibited decreased bacterial load, PMN infiltrate, and corneal mRNA levels for IL-1beta, MIP-2, and TNF-alpha. Th2-type cytokines (IL-4, -5, -10) also were significantly upregulated, and protein levels for TNF-alpha and IL-10 confirmed the mRNA data. To further investigate IL-33 in corneal inflammation, it was overexpressed in Mvarphi (RAW264.7 cells). This significantly increased IL-5 and IL-10, while it decreased IFN-gamma and other pro-inflammatory cytokines. The role of the Mvarphi was further tested in infected rmIL-33 compared with PBS-injected mice. Immunostaining showed that rmIL-33 injection shifted Mvarphi polarization from NO synthase 2 to arginase production. Furthermore, peritoneally elicited cells (B6 mice) treated with lipopolysaccharide and rmIL-33 exhibited elevated ST2 levels and a shift from IL-12 to IL-10 mRNA production.


CONCLUSIONS
These data provide evidence that IL-33 promotes a Th2-type immune response and reduces inflammation by polarizing the Mvarphi production of anti-inflammatory mediators in the cornea.
Hazlett
Linda D
LD
Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA. lhazlett@med.wayne.edu
McClellan
Sharon A
SA
Barrett
Ronald P
RP
Huang
Xi
X
Zhang
Yunfan
Y
Wu
Minhao
M
van Rooijen
Nico
N
Szliter
Elizabeth
E
D000818:Animals; D001119:Arginase / Q000378:metabolism; D003320:Corneal Ulcer / Q000276:immunology / Q000517:prevention & control*; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D019573:Epithelium, Corneal / Q000378:metabolism*; D015818:Eye Infections, Bacterial / Q000276:immunology / Q000517:prevention & control*; D005260:Female; D000067596:Interleukin-33; D007378:Interleukins / Q000502:physiology*; D017737:Macrophages, Peritoneal / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009504:Neutrophils / Q000276:immunology; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D011552:Pseudomonas Infections / Q000276:immunology / Q000517:prevention & control*; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018417:Th1 Cells / Q000276:immunology; D018418:Th2 Cells / Q000276:immunology; D015854:Up-Regulation
C506535:Il33 protein, mouse; D000067596:Interleukin-33; D007378:Interleukins; D012333:RNA, Messenger; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C544448:Arg1 protein, mouse; D001119:Arginase