Enhanced expression of mucin genes in a guinea pig model of allergic asthma

The ovalbumin (OVA)-sensitized guinea pig is often used as an animal model of asthma and airway hyperreactivity. A characteristic lesion of asthma is excessive production of mucin in the airways. Mechanistic studies of this lesion in guinea pigs have been limited due to lack of mucin gene probes for this species. The aim of the present study was to clone the cDNAs encoding two major airway mucins (Muc2 and Muc5ac) from the guinea pig, and investigate mucin gene expression in lungs of sensitized animals in response to antigen challenge. We isolated and sequenced two cDNA fragments coding for the sequences located within the carboxyl-terminal cysteine-rich region of guinea pig Muc2 and Muc5ac mucins. Comparison of cloned cDNAs with those from other species revealed high degrees of sequence identity and conservation of all cysteine residues in deduced primary sequences. Based on the resultant sequence information, we also designed oligonucleotide primers for specific detection of guinea-pig Muc2 and Muc5ac steady-state mRNA levels via reverse transcriptase/ polymerase chain reaction (RT-PCR). Levels of both Muc2 and Muc5ac mRNA in lungs of OVA-sensitized guinea pigs increased significantly by 30 min after an acute exposure to 0.3% OVA. In addition, levels of eotaxin mRNA also increased in these tissues, but the increases were not significant until 2 h after challenge. Correspondingly, the number of eosinophils in bronchoalveolar lavage fluid did not increase until 4 h postchallenge. Results of these studies suggest that the OVA-sensitized guinea pig responds to allergic challenge with enhanced expression of genes (e.g., eotaxin, Muc2, and Muc5ac) that likely play a role in increased airway inflammation and mucin overproduction, and enhanced mucin gene expression appears to occur before eosinophil infiltration.