Matrix metalloproteinases (MMPs) are a family of proteinases which have zinc dependent structure centre, widely degrade extracellular matrix components and cleave non-matrix proteins including growth factors, chemoattractants and cell surface receptors.1) Most of the MMPs contain pro-domain which is accordant, through binding of the cysteine of pro-domain and histidines of the catalytic domain, to the metallo cation Zn 2ϩ . MMPs are activated by cleavage to set the catalytic domain free to act on substrates.MMP-12, which is also called metalloelastase and macrophage elastase, was firstly detected in mouse peritoneal macrophage.2) Subsequently, it was also found in alveolar macrophages, 3,4) bronchial epithelial cells 5) and airway smooth muscle cells. 6) Like other MMPs, MMP-12 consists of a pro-domain, a catalytic domain and a hemopexin domain, and is activated by taking off the pro-domain and then the hemopexin domain remaining the catalytic domain. It has been reported that the rat MMP-12 catalytic domain can degrade collagen-V and partially degrade collagen-I 7) and other extracellular matrix proteins.
8)Although the role of MMP-12 in airways is not fully understood, an involvement of MMP-12 has been reported in cigarette smoking-associated airway inflammatory diseases, such as chronic obstructive pulmonary disease (COPD).
9)MMP-12 has been reported to be associated with cigarette smoke-induced emphysema 10) and macrophage migration.
11)In patients with COPD, MMP-12-positive macrophages were increased in airway epithelial layers and bronchoalveolar lavage fluids when compared with normal subjects. 12) On the other hand, an upregulation of MMP-12 was also found in a mouse model of airway inflammation and remodeling induced by IL-13.13) Furthermore, an increased expression of MMP-12 was reported in a mouse model of allergic airway inflammation: the MMP-12 upregulation was not observed in IL-13-knockout mice.14) It is thus possible that MMP-12 is also relating to airway diseases mediated by Th2 cytokines such as allergic bronchial asthma. Indeed, MMP-12 has been proposed as one of the asthma candidate genes. 15) In the present study, the changes in the expression and localization of MMP-12 in airways of repeatedly antigen-challenged rats were investigated to reveal whether or not MMP-12 has relevance to allergic bronchial asthma.
MATERIALS AND METHODS
Sensitization and Antigenic ChallengeMale Wistar rats (6 weeks of age, specific pathogen-free, 170-190 g; Charles River Japan, Inc.) were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen (DNP-Asc) by the method described in the previous papers. [16][17][18][19][20][21][22][23][24] In brief, the rats were sensitized with DNP-Asc together with Bordetella pertussis and were boosted 5 d later. Eight days after the first immunization, the rats were challenged by inhaling DNP-Asc for 40 min under conscious state. Then the animals were subjected to totally three times repeated antigen challenge every 48 h with the same inhalational cha...