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Published on: August 2, 2021
IL-33 shifts macrophage polarization, promoting resistance against Pseudomonas aeruginosa keratitis
Linda D Hazlett1, Sharon A McClellan, Ronald P Barrett
1Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA. lhazlett@med.wayne.edu
Purpose:
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.
Insights
Interleukin-33 (IL-33) enhances resistance to Pseudomonas aeruginosa keratitis by promoting a T-helper 2 (Th2) immune response. IL-33 also reduces inflammation through macrophage polarization, leading to anti-inflammatory mediator production in the cornea.
Area of Science:
- Immunology
- Ophthalmology
- Microbiology
Background:
- Pseudomonas aeruginosa keratitis is a serious eye infection.
- The role of interleukin-33 (IL-33) in ocular defense against bacterial keratitis is not fully understood.
- Understanding immune responses in keratitis is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the function of IL-33 in the context of Pseudomonas aeruginosa keratitis.
- To determine if IL-33 influences disease severity and immune cell infiltration in the cornea.
- To explore the impact of IL-33 on T-helper cell polarization and macrophage activity during infection.
Main Methods:
- Compared IL-33 expression in susceptible (C57BL/6) and resistant (BALB/c) mice during infection.
- Administered recombinant mouse IL-33 (rmIL-33) to susceptible mice to assess its effects on disease.
- Analyzed bacterial load, immune cell infiltration (PMNs), cytokine profiles (RT-PCR), and macrophage polarization (immunostaining).
Main Results:
- IL-33 levels were elevated in resistant mice post-infection.
- rmIL-33 treatment in susceptible mice reduced disease severity, bacterial load, and PMN infiltration.
- IL-33 promoted a T-helper 2 (Th2) cytokine profile (IL-4, IL-5, IL-10) and shifted macrophages towards an anti-inflammatory phenotype (arginase production).
Conclusions:
- IL-33 plays a protective role in Pseudomonas aeruginosa keratitis.
- IL-33 promotes Th2 immune responses and reduces corneal inflammation.
- Macrophage polarization induced by IL-33 contributes to the anti-inflammatory effect.
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