Abstract
Abstract: :
Purpose: IFN–γ is an important Th1 type cytokine that plays a major role in bacterial killing and development of the resistance phenotype following P. aeruginosa infection in BALB/c mice (Huang et al., J. Immunol. 2002;168:5756.). Since T cells are not normally detectable in the corneas of these mice after P. aeruginosa infection, the purpose of this study was to identify the source of corneal IFN–γ.Methods:BALB/c mice were injected intraperitoneally (i.p.) with anti–asialoGM1 pAb (Wang et al., J. Immunol. 1998;160:1098.) to deplete Natural Killer (NK) cells, (efficiencey confirmed by immunostaining), while control mice received normal rabbit serum on –2, day of infection (0) and 5 days post–infection (p.i.) with 1.0x106 CFU P. aeruginosa, ATCC 19660. Ocular disease was graded by clinical score for 7 days p.i. Viable bacteria in cornea were quantitated by plate count at days 3 and 5 p.i. At the latter time points, a myeloperoxidase (MPO) assay was performed in both groups to quantitate the number of PMN infiltrating the cornea after infection. At 3 and 5 days p.i., corneas from NK–cell depleted and control mice were collected and mRNA levels of IFN–γ measured by real time PCR. Results: Clinical scores were significantly different in anti–asialoGM1–vs. control–treated mice at days 1, 3, 5 and 7 p.i. (p= 0.0047, 0.0357, 0.0003, <0.0001, respectively). All corneas in the NK–cell depleted group perforated by day 5 p.i. vs. no perforation in the rabbit serum treated controls. Viable bacteria were increased in NK–cell depleted vs. control mice at 3 (p=0.0424) and 5 (p=0.0144) days p.i. Significantly increased MPO activity (more PMN) was detected in NK–cell depleted BALB/c compared to rabbit serum–treated mouse cornea at days 3 and 5 p.i. (p=0.0002 and 0.0012, respectively). IFN–γ mRNA levels were similar in both groups at day 3 p.i., however at day 5 p.i., significantly (p=0.0011) lower mRNA levels were detected in the cornea of the NK–cell depleted vs. control animals. Conclusion:NK cells are a major source of IFN–γ in the cornea of BALB/c mice after P. aeruginosa corneal infection and these cells are required to effectively regulate bacterial killing and PMN number in the cornea of these mice. Support: R01EY02986; P30EY04068
Keywords: Pseudomonas • immunomodulation/immunoregulation