IL-18 contributes to host resistance against infection with Pseudomonas aeruginosa through induction of IFN-gamma production.
Pseudomonas aeruginosa keratitis destroys the cornea in susceptible (B6), but not resistant (BALB/c) mice. To determine mechanisms mediating resistance, the role of IFN-gamma, IL-12, and IL-18 was tested in BALB/c mice. RT-PCR analysis detected IFN-gamma mRNA expression levels in cornea that were significantly increased at 1-7 days postinfection. IL-18 mRNA was detected constitutively in cornea and, at 1-7 days postinfection, levels were elevated significantly, while no IL-12 mRNA was similarly detected. To test whether IL-18 contributed to IFN-gamma production, mice were treated with anti-IL-18 mAb. Treatment decreased corneal IFN-gamma mRNA levels, and bacterial load and disease increased/worsened, compared with IgG-treated mice. To stringently examine the role of IFN-gamma in bacterial killing, knockout (-/-) vs wild-type (wt) mice also were tested. All corneas perforated, and bacterial load was increased significantly in -/- vs wt mice. Because disease severity was increased in IFN-gamma(-/-) vs IL-18-neutralized mice, and since IL-18 also induces production of TNF, we tested for TNF-alpha in both groups. ELISA analysis demonstrated significantly elevated corneal TNF-alpha protein levels in IFN-gamma(-/-) vs wt mice after infection. In contrast, RT-PCR analysis of IL-18-neutralized vs IgG-treated infected mice revealed decreased corneal TNF-alpha mRNA expression. Next, to resolve whether TNF was required for bacterial killing, TNF-alpha was neutralized in BALB/c mice. No difference in corneal bacterial load was detected in neutralized vs IgG-treated mice. These data provide evidence that IL-18 contributes to the resistance response by induction of IFN-gamma and that IFN-gamma is required for bacterial killing.
Huang
Xi
X
Department of Anatomy/Cell Biology, Wayne State University School of Medicine, Detroit, MI 48201.
McClellan
Sharon A
SA
Barrett
Ronald P
RP
Hazlett
Linda D
LD
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D003315:Cornea / Q000276:immunology / Q000382:microbiology; D005260:Female; D007371:Interferon-gamma / Q000096:biosynthesis* / Q000235:genetics; D018664:Interleukin-12 / Q000235:genetics; D020382:Interleukin-18 / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D011552:Pseudomonas Infections / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification; D012333:RNA, Messenger / Q000032:analysis
D000911:Antibodies, Monoclonal; D020382:Interleukin-18; D012333:RNA, Messenger; D018664:Interleukin-12; D007371:Interferon-gamma