山口 泰弘

OBJECTIVE: Recently, human beta-defensin-2 (hBD-2), an inducible defensin, has been reported to be involved in innate immunity and host defence. To examine the exact roles of hBD-2 in the respiratory system, we examined the molecular mechanisms of hBD-2 gene expression in vitro. METHODOLOGY: Using a human airway cell line (LC-2/ad), lipopolysaccharide (LPS)-induced gene expression of hBD-2 was studied in the absence or the presence of (i) dexamethasone, (ii) inhibition of NF-kappaB and AP-1, (iii) intracellular calcium chelator, and (iv) cyclooxygenase (COX) inhibitors. RESULTS: Lipopolysaccharide-induced gene expression of hBD-2 was down-regulated by (i) dexamethasone, (ii) inhibition of NF-kappaB and AP-1, and (iii) intracellular calcium chelator. However, COX inhibitors had no effect on LPS-induced mRNA expression of hBD-2. CONCLUSION: These findings suggest that glucocorticoids (GC), but not COX inhibitors, reduce hBD-2 gene expression, while NF-kappaB, AP-1 and intracellular calcium are essential for hBD-2 expression. Glucocorticoid-induced down-regulation of hBD-2 might be involved in the GC-induced suppression of respiratory host defence associated with hBD-2.

Bronchial hyperresponsiveness and eosinophilia are major characteristics of asthma. Calcitonin gene-related peptide (CGRP) is a neuropeptide that has various biological actions. In the present study, we questioned whether CGRP might have pathophysiological roles in airway hyperresponsiveness and eosinophilia in asthma. To determine the exact roles of endogenous CGRP in vivo, we chose to study antigen-induced airway responses using CGRP gene-disrupted mice. After ovalbumin sensitization and antigen challenge, we assessed airway responsiveness and measured proinflammatory mediators. In the sensitized CGRP gene-disrupted mice, antigen-induced bronchial hyperresponsiveness was significantly attenuated compared with the sensitized wild-type mice. Antigen challenge induced eosinophil infiltration in bronchoalveolar lavage fluid, whereas no differences were observed between the wild-type and CGRP-mutant mice. Antigen-induced increases in cysteinyl leukotriene production in the lung were significantly reduced in the CGRP-disrupted mice. These findings suggest that CGRP could be involved in the antigen-induced airway hyperresponsiveness, but not eosinophil infiltration, in mice. The CGRP-mutant mice may provide appropriate models to study molecular mechanisms underlying CGRP-related diseases.

Defensins comprise a family of cationic antimicrobial peptides that are characterized by the presence of six conserved cysteine residues. We identified two novel human beta-defensin (hBD) isoforms by mining the public human genomic sequences. The predicted peptides conserve the six-cysteine motif identical with hBD-4, termed hBD-5 and hBD-6. We also evaluated the characteristics of the mouse homologs of hBD-5, hBD-6, and HE2beta1, termed mouse beta-defensin (mBD)-12, mBD-11, and mouse EP2e (mEP2e). The mBD-12 synthetic peptide showed salt-dependent antimicrobial activity. We demonstrate the epididymis-specific expression pattern of hBD-5, hBD-6, mBD-11, mBD-12, and mEP2e. In situ hybridization revealed mBD-11, mBD-12, and mEP2e expression in the columnar epithelium of the caput epididymis, contrasting with the predominant expression of mBD-3 in the capsule or septum of the whole epididymis. In addition, the regional specificity of mBD-11, mBD-12, and mEP2e was somewhat overlapping, but not identical, in the caput epididymis, suggesting that specific regulation may work for each member of the beta-defensin family. Our findings indicated that multiple beta-defensin isoforms specifically and cooperatively contribute to the innate immunity of the urogenital system.