In the present study the gene expression of DEFA 1/3 ad DEFA 4 was analyzed in healthy salivary gland tissue in comparison with different benign and malignant salivary gland tumours and inflamed salivary gland tissue. Additionally the peptides were visualized by immunostaining.
Both α-defensins were detectable in healthy tissue, inflamed tissue as well as tumour tissue. In comparison with healthy salivary gland tissue, which was taken as baseline, the gene expression of DEFA 1/3 and DEFA 4 was altered in all investigated tissues – but most interesting were the findings in cystadenolymphomas and pleomorphic adenomas (Tables 2 and 3):
Cystadenolymphomas, although first mentioned by Hildebrad in 1885  and more precisely described by the German pathologist Albrecht in 1910  are named “Warthin tumor” after the American pathologist Aldred Warthin who published 34 years later the first two cases of this entity in American literature . Cystadenolymphomas are composed of a bilayered oncocytic and basaloid epithelium, forming cystic structures, papillae and glands that are accompanied by a dense lymphoid stroma [29–31]. Their origin is still a kind of cryptic today: some authors think that they might develop of heterotopic epithelial tissue enclosed in the lymph nodes within the parotid gland whereas others believe that they are adenomas with a lymphocytic infiltration [29–31]. But Interestingly recent studies have shown, that the above mentioned epithelial component is polyclonal, which means that it does not exhibit the clonal allelic losses which are typical for a true neoplasm . This finding is supported by the present and further studies of our group concerning the gene expression and distribution of AMPs in different lesions of the salivary glands.
Among the benign salivary gland tumours, pleomorphic adenomas are by far the most frequent adenoma of the parotid gland, whereas oxyphil adenomas and other monomorphic adenoma seem to be seldom . As pleomorphic adenomas show very distinct molecular features concerning the β-defensins which differ from other benign salivary gland tumours, it seems unlikely, that cystadenolymphomas are adenomas with a lymphocytic infiltration [4–6]. A nuclear shift of the hBD-1 gene product and a decrease of hBD-1 gene expression underlines their potency for a malignant transformation into adenocarcinomas [4, 5]. In vitro deficiency of insulin-like growth factor-1 (IGF-1) and a low basic hBD-2 and hBD-3 gene expression could be protective against a malignant transformation .
Because of this recent evidence that β-defensin might play an important role in the formation and malignant progression of salivary gland tumours, because of their structural and functional similarities and their gene loci on chromosome 8, the present study focused on the α-defensins. The increase of DEFA 1/3 gene expression was in pleomorphic adenomas only slight, but in cystadenolymphomas very explicit. The increase of DEFA 4 was in cystadenolymphomas 48.2-fold, but in pleomorphic adenomas there was a 3.4-fold decrease in DEFA 4 gene expression. This inversely alteration of DEFA 4 gene expression and the abundantly clear difference in DEFA 1/3 gene expression additionally contradict the hypothesis of cystadenolymphomas being adenomas with a lymphocytic infiltration. The comparable increase of DEFA 1/3 and DEFA 4 in inflamed salivary gland tissue (146.9 and 30.3-fold respectively) and cystadenolymphomas (146.9 and 48.2-fold respectively) might suggest an inflammatory aetiology and supports the theory, that cystadenolymphomas due to their polyclonal epithelial component are not a true neoplasm .
Pleomorphic adenomas, presenting as benign mixed tumours, are the most common neoplasms of the major salivary glands. Although benign, it is not uncommon for pleomorphic adenomas to recur, and a subset of them might undergo a malignant transformation . In prior studies the authors demonstrated, that pleomorphic adenomas differ from other salivary gland tumour in their β-defensin gene expression and the cellular distribution of the hBD-1 gene product [4–6]. The down-regulation of hBD-1 gene expression is an event which could be observed in many tumour entities [16–21] and which is common in head and neck cancers also [4–6, 16–21]. Additionally an up-regulation of hBD-3 was observed in oral squamous cell carcinomas (OSCC) [19, 20]. This observation led to the hypothesis that in OSCCs hBD-1 works as a tumour-suppressor, whereas hBD-3 is a proto-oncogene – which could be verified by in vitro experiments . In the present study pleomorphic adenomas clearly differ from other salivary gland tumours by their α-defensin gene expression as well: In comparison with healthy salivary gland tissue the increase of DEFA 1/3 gene expression was clearly in adenocarcinomas, adenoidcystic carcinomas and mucoepidermoid carcinomas, but only slight in pleomorphic adenomas. The gene expression of DEFA 4 was elevated in all lesions but only in pleomorphic adenomas there was as 3.4-fold decrease. This distribution of DEFA 4 gene expression is evocative of hBD-1 gene expression in pleomorphic adenomas and other head and neck cancers. It seems to be likely, that α-defensins as well as β-defensins are involved in tumour formation and progression of salivary gland tumours - but the interpretation of α-defensin gene expression in different head and neck lesions remains difficult and particularly inconsistent. For example in oral leukoplakia DEFA 4 is highly up-regulated (179.2-fold) whereas DEFA 1/3 does not differ much from healthy gingiva . In irritation fibromas of the oral cavity it is vice versa: DEFA 1/3 is up-regulated (14-fold) and DEFA 4 is comparable to gingiva . For this reason our group at the moment carefully investigates the influence of α-defensins in different head and neck tumours in vitro. To have this knowledge will help us to a better understanding of the molecular mechanisms which make a benign tumour malignant and could therefore enable us in the future to early diagnose and treat these tumours.