Response of Periodontal Tissue Produced by E. coli Endotoxin Injections in Immunized and Non-immunized Rats

Examinations were made to elucidate histopathological changes of periodontal tissues in immunized and non-immunized conventional (CV) rats. The immunization was produced by single periodontal injection of E. coli endotoxin. The following results were obtained: 1) Anti-endotoxin titer of the rat serum was measured by the passive hemagglutination (PHA) test. Anti-endotoxin serum in rats ranged between 26 and 28. 2) The titer of five series of serum of eight nonimmunized rats against E. coli O111: B4 coated SRBC, ranged between 20 to 22. 3) Even after the topical endotoxin stimulation, the serum anti-endotoxin titer maintained almost the same level in pre-immunized rats. On the other hand, PHA titer produced by topical application of endotoxin in non-immunized rats increased gradually from 20 to 22 in 24-48 hours and reached to the range between 24 and 25 PHA titer at one week. Histo-pathological changes observed were as follows: Both in pre-immunized and non-immunized rats, exudative inflammation was observed in the gingival tissue after topical endotoxin stimulation. Significant neutrocyte infiltration was observed between 24 and 48 hours after the topical stimulation. Marked lymphocyte infiltration was observed between 72 and 96 hours after the stimulation. At this period, plasma cells and fibroblasts were also observed. Topical gingival endotoxin stimulation in pre-immunized rats induced severer exudative inflammation in the gingival tissue than in non-immunized rats. Although marked inflammatory responses were resulted in soft tissues of pre-immunized rats after the stimulation, inflammatory bone resorption was not pronounced in all of the specimens examined.