ラット歯髓腔への内毒素 (LPS) 接種後の免疫反応に関する研究

抄録

Gram-negative microorganisms are usually found in infected root canals with necrotic pulps. The outer membrane of these microorganisms contains lipopolysaccharide complexes (LPS), so-called endotoxins. Endotoxins are capable of initiating various biological effects. Especially, endotoxins have been demonstrated to activate the complement pathways and to stimulate the degranulation of mast cells. These events result in increase of the vascular permeability, inducement of the polymorphonuclear leucocyte (PMN) chemotaxis, and resorption of the bone. Therefore, endotoxins seem to play an important role in the development of pulpal and periapical disease. The purpose of this thesis is to investigate the effects of endotoxins after inoculating Escherichia coli-LPS into the pulp chambers in rats. The animals were divided into following three groups : 1. repeated applications of LPS (0.6μg) in the pulp chambers of the right mandibular molars ; 2. repeated applications of LPS (6μg) in the pulp chambers of the right mandibular molars ; 3. repeated applications of LPS (6μg) in the pulp chambers of the right mandibular incisor. The responses against LPS were studied in the ratio of T-cells and B-cells in the submandibular lymph nodes by using rosette technique, serum titers by using the indirect hemagglutination test and the complement fixing test, and the histological evaluations. The results obtained were as follows : 1. In the experimental side of the submandibular lymph nodes, the ratio of T-cells slightly changed during experimental period, regardless of the inoculating regions (molars or incisor) and the dose of LPS (0.6μg or 6μg). In contrast, that of B-cells significantly increased on the 7-21st day after the first inoculation, when LPS was administered to the incisor. In the non-experimental side of the submandibular lymph nodes, the ratio of T-cells and B-cells showed no notable changes in all groups. 2. In the results of the indirect hemagglutination test and the complement fixing test, the serum titer following the inoculations into the incisor was greater than that into molars. The larger amounts LPS administered, the higher titers detected. The hemagglutinating antibody responses were somewhat greater than the complement fixing antibody responses. 3. In histological findings, the specimens of all groups showed acute inflammatory lesions during experimental period. These responses were characterized by extreme disturbance of circulation and intense PMN infiltration. On the 28th day after the first inoculation, marked bone resorption was observed in the group of repeated applications of LPS (6μg). The results of this study suggest that endotoxins (LPS) may have an important role in pulpal and periapical lesions by biological activity, and immunological activity which seems to mainly elicite humoral immune responses.