VIP promotes resistance in the Pseudomonas aeruginosa-infected cornea by modulating adhesion molecule expression.

Purpose: This study tested the hypothesis that the neuropeptide vasoactive intestinal peptide (VIP) regulates adhesion molecule expression, reduces inflammatory cell migration and infiltration into the Pseudomonas aeruginosa-infected cornea of susceptible B6 mice, and promotes corneal healing and resistance.

Methods: B6 mice received daily intraperitoneal (IP) injections of VIP from -1 through 5 days after infection. Control mice were similarly injected with sterile phosphate-buffered saline (PBS). Transcript levels of adhesion molecules were determined by PCR array, then select molecules were tested individually by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and confirmed at the protein level by enzyme-linked immunosorbent assay (ELISA) or immunofluorescent staining with confocal laser scanning microscopy at various time points after infection to assess the effects of VIP treatment in the regulation of adhesion molecule expression.

Results: Injection of B6 mice with VIP compared with PBS resulted in significant downregulation of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, platelet-endothelial cell adhesion molecule-1, and P-selectin and L-selectin mRNA expression. Protein levels for ICAM-1 and VCAM-1, detected by ELISA, supported the mRNA data at similar time points. Immunofluorescence staining further confirmed the effects of VIP treatment, showing reduced corneal expression of ICAM-1/leukocyte function-associated antigen (LFA-1) and VCAM-1/very late antigen-4 (VLA-4) at select time points compared with PBS-treated animals.

Conclusions: VIP treatment downregulates the production of adhesion molecules integral to the transmigration process of host inflammatory cells (polymorphonuclear neutrophils, macrophages) into the infected cornea. This results directly in reduced cellular infiltration, less stromal destruction, and better disease outcome.