Substance P promotes susceptibility to Pseudomonas aeruginosa keratitis in resistant mice: anti-inflammatory mediators downregulated.
OBJECTIVE
Studies have shown that blocking substance P (SP) binding to neurokinin 1 receptor with spantide I prevents Pseudomonas aeruginosa-induced corneal perforation in susceptible C57BL/6 mice. This study tested the effect of SP injection on the resistance response (cornea heals) of BALB/c mice.


METHODS
The day before infection, mice were injected intraperitoneally with SP or PBS. Disease was graded by clinical score, slit lamp, plate count, real-time RT-PCR, and ELISA assays, and polymorphonuclear neutrophils (PMNs) were quantitated using a myeloperoxidase assay. In additional experiments, BALB/c mice were injected intraperitoneally with vasoactive intestinal peptide (VIP) antagonist and similarly analyzed.


RESULTS
Mice injected with SP exhibited worsened disease on days 1 to 7 after infection compared with controls. SP injection resulted in elevated PMN levels and viable bacterial counts in the cornea 3 and 5 days after infection. mRNA expression for NFkappaB and type 1 cytokines (e.g., IFN-gamma), as well as for TNF-alpha, MIP-2, IL-18, IL-6, and IL-1beta, were significantly elevated, whereas VIP and cytokines TGF-beta and IL-10 were significantly reduced. Differences in mRNA expression were selectively confirmed at the protein level by ELISA for NFkappaB, IL-1beta, and IL-10. VIP antagonist treatment also resulted in exacerbated disease scores, elevated proinflammatory mediators, and reduced anti-inflammatory mediators.


CONCLUSIONS
These data provide evidence that the neuropeptide SP, among its broad systemic effects, is a potent neuroimmunoregulator that promotes susceptibility in the resistant BALB/c mouse by overcoming the anti-inflammatory effects of VIP and IL-10 and that a balance between SP and VIP levels may be critical in disease resolution.
McClellan
Sharon A
SA
Department of Anatomy & Cell Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201, USA.
Zhang
Yunfan
Y
Barrett
Ronald P
RP
Hazlett
Linda D
LD
D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D003320:Corneal Ulcer / Q000276:immunology / Q000382:microbiology*; D016207:Cytokines / Q000235:genetics; D004198:Disease Susceptibility; D015536:Down-Regulation / Q000187:drug effects*; D004797:Enzyme-Linked Immunosorbent Assay; D015818:Eye Infections, Bacterial / Q000276:immunology / Q000382:microbiology*; D005260:Female; D018836:Inflammation Mediators / Q000378:metabolism*; D007694:Killer Cells, Natural / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D018613:Microscopy, Confocal; D016328:NF-kappa B / Q000235:genetics; D009504:Neutrophils / Q000502:physiology; D011552:Pseudomonas Infections / Q000276:immunology / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013373:Substance P / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D018417:Th1 Cells / Q000276:immunology; D014660:Vasoactive Intestinal Peptide / Q000037:antagonists & inhibitors / Q000378:metabolism
D016207:Cytokines; D018836:Inflammation Mediators; D016328:NF-kappa B; D012333:RNA, Messenger; D013373:Substance P; D014660:Vasoactive Intestinal Peptide; C042867:spantide