慢性根尖性歯周炎の主病巣は線維芽細胞と血管芽細胞の過剰増殖より成る肉芽組織で、感染根管からの感染による慢性増殖性炎を原病巣としている。今回、b-FGF、IL-1α、TGF-α、TGF-β1、HGF、TNF-α、EGF、PDGFとこれらのレセプターのFGFR(Bek)、IL-1R、TGFβRI、TGFβR II、HGFR、TNFR、EGFR、PDGFRαについて、60例の慢性根尖性歯周炎を病理組織学的にI型からVI型に分け、各病型における各増殖因子とレセプターの発現の特徴を免疫組織化学的に検索した。続いて、感染根管から採取した細菌の培養菌(Wb)と純培養したActinomyces naeslunndii ATCC12104(An)をラットの頬粘膜に接種し、50日間にわたる実験的感染病巣における経時的動態を検索した。各種病型は、I型(膿瘍の形成を伴う病型、15例)、II型(病巣のほとんどが肉芽腫より成り多数の好中球の浸潤を伴う病型、10例)、III型(II型と同様の肉芽腫性病変で好中球の浸潤のない病型、10例)、IV型(歯根肉芽腫の一型で線維成分が多く肉芽組織の少ない病型、15例)、V型(IV型よりも線維成分が多く肉芽組織が30%以下の病型、5例)、VI型(硬化性根尖性歯周炎の病型、5例)とした。慢性根尖性歯周炎のIII型はI型の治癒型であり、II型はその一過程にある病型かあるいはIII型からI型への再燃過程にあり、IV型やV型はVI型へ向う病巣であることがそれぞれ示唆された。一方、実験的感染病巣はいずれも膿瘍が生じ、肉芽組織性膿瘍膜が形成されたが、An接種群では広範な肉芽組織を形成し、Mφや増殖因子の発現細胞はWB接種群よりも明らかに多かったことから、慢性根尖性歯周炎の肉芽腫性変化に根管内細菌の主要細菌と目されているActinomycesの関わりが深いことも伴わせて示唆された。The mechanism of granuloma formation due to chronic apical periodontitis This study is focused on the chronic apical periodontitis consists of granulation tissue formed by proliferation of fibroblasts and angioblasts during chronic proliferative inflammation due to infected root canal. The overgrowth of fibroblasts and angioblasts is considered directly caused by the expression of several growth factors and receptors. The relationship between the expression of growth factors [basic fibroblast growth factor(bFGF), Interlukin-1α(1L-1α), transforming growth factor-α and -β1(TGF-α and -β1), hepatocyte growth factor(HGF), tumor necrosis factor-α(TNF-α), epidermal growth factor(EGF), platelet derived growth factor(PDGF)] and their receptors(FGFR, IL-1R, TGF-R I and -RI II , HGFR, TNFR, EGFRand PDGFR)was analyzed by immunohistochemical study. The rat lesion induced by bacterial injection obtained from a human root canal was also analyzed. The chronic apical periodontitis(60 cases)were classified into six types lesions based on histopathological findings as follows; Type I(abscess formation; 15 cases), Type II(leukocyte infiltration; 10 cases), Type III(granulation without abscess or inflammatory cells infiltration; 10 cases), Type IV(granulation with fibrous tissue;15cases), Type V(fibrous tissue lesser granulation; 5 cases), and Type VI(scar tissue; 5 cases). Immunohistochemistry demonstrated that CD68-positive macrophages comprise an overwhelming majority of the inflammatory cells in the granulation tissue of chronic apical periodontitis, and these cells are the principal source of IL-1α, TGF-α, TGFβ1, b-FGF and PDGF. IL-1R, TGFβRI, TGFβRII, FGFR and PDGFR were expressed by fibroblasts, vascular endothelial cells and lymphocytes. The experimental infection of bacteria from a human root canal demonstrated that abscess formation occurs during several days after bacterial infection into rat buccal mucosa and CD68 positive macrophages infiltrate accompanying the abscess formation. Based on these findings, it was suggested that chronic apical periodontitis, classified into Type I to Type III, was suggested to comprise transforming types during the healing. Type IV was regarded as a healing type with scar tissue formation progressing in Type V. The granulation tissue, the foci of Type I, Type II and Type III and/or Type IV is considered to be the major lesion, which forms granuloma as a function of IL-1α, b-FGF, PDGF, IL-1R, FGFR and PDGFR producing.