CHANGE OF SALIVARY IGA SECRETION AND CARIES DEVELOPMENT IN IRRADIATEDRATS

Xerostomia is a serious side-effect of radiotherapy for head and neck cancer and often enhances caries activity. However, the relationship b etween caries induction and the IgA level in saliva in rats subjected to irradiation of the salivary glands is unclear. The effect of saliva ry gland irradiation on salivary function was examined in specific pat hogen-free Sprague-Dawley rats infected with or without Streptococcus mutans MT8148R (serotype c). The flow rate of saliva and the protein c oncentration in saliva were significantly reduced in irradiated rats, regardless of infection of S. mutans. The caries activity was enhanced in these rats, and an irradiation level of 50 Gy significantly increa sed the caries score. However, longitudinal study indicated that the s alivary concentration of IgA reactive with S. mutans whole cells maint ained similar or significantly higher levels in irradiated rats, when compared with those of nonirradiated rats. In addition, there was no n egative correlation between the caries score and the salivary concentr ation of IgA reactive with S. mutans. These findings suggest that the secreted IgA against S. mutans may not play a significant role in the caries induction of hyposalivated rats.