Defensins In Ocular Immunity

Corneal infection with P. aeruginosa results in corneal perforation in susceptible B6, but not resistant BALB/c mice. This study explored their role mBD 1-4 in corneal infection, and their potential synergy. Immunostaining and real-time RT-PCR data demonstrated that their expression was either constitutive (mBD1 and mBD2) or inducible (mBD3 and mBD4) in normal BALB/c and B6 corneas, and disparately regulated in BALB/c vs B6 corneas after infection. Knock down studies using siRNA treatment indicated that mBD2 and mBD3, but neither mBD1 nor mBD4, is required in ocular defense. Moreover, in vivo studies demonstrated individual and combined effects of mBD2 and mBD3 that modulate bacterial load, PMN infiltration, and production of pro-inflammatory molecules (e.g., IFN-gamma, MIP-2, IL-1beta, TNF-alpha), iNOS, as well as TLR signaling molecules (e.g., TLR2, TLR4, MyD88) and transcription factor NF-kappaB. Most notably, bacterial load was increased at 5 days p.i. by silencing either mBD2 or mBD3, but was elevated at both 1 and 5 days p.i. when silencing both defensins. PMN infiltration was increased at 1 day p.i. by silencing both defensins or mBD3, but not mBD2 alone. iNOS expression was elevated by silencing mBD2, but reduced after silencing mBD3 or both defensins. Additionally, cell sources of mBD2 and mBD3 in corneal stroma were identified by dual label immunostaining after infection: PMN produce both defensins, whereas macrophages and fibroblasts produce mBD2 but not mBD3. Collectively, the data provide evidence that mBD2 and mBD3 together promote resistance against corneal infection. The conclusions may be relevant to potential treatment of other ocular diseases, in addition to P. aeruginosa keratitis