Interleukin-1β (IL-1β) has been considered as a major potent mediator of bone resorption and implicated in the development of human periapical lesions. Among naturally occurring interleukin-1 (IL-1) inhibitors, IL-1 receptor antagonist (IL-1ra) is a 22 kDa protein that shares homology with IL-1β and IL-1 a, binds to IL-1 receptor with similar affinity to IL-1, and has no known agonist properties. In this study, we measured the periapical exudate (PE) levels of IL-1β and IL-1ra from human periapical lesions. PE samples were collected from root canals during routine endodontic treatments, and the enzyme-linked immunosorbent assay was used to measure PE-IL-1β and IL-1ra. Detectable levels of both IL-1β and IL-1ra were found in 25 of 29 clinical samples. Relatively high levels of IL-1ra compared with IL-1β (mean IL-1ra:IL-1β ratio = 128.7; range: 0.9 to 495.4), and significantly positive correlation between IL-1ra and IL-1β levels was found. The PE-IL-1ra:IL-1β ratios obtained from symptomatic lesions were significantly lower than those from asymptomatic lesions. These results suggest that IL-1ra-mediated IL-1 antagonism occurred to block locally produced IL-1 activity, and the balance of IL-1 to IL-1ra production may be crucial in the development of periapical lesions.
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