RESUMEN
AIM: To characterize the histologic and cellular response to A. actinomycetemcomitans (Aa) infection. MATERIAL & METHODS: Wistar rats infected with Aa were evaluated for antibody response, oral Aa colonization, loss of attachment, PMN recruitment, TNF-α in the junctional epithelium and connective tissue, osteoclasts and adaptive immune response in local lymph nodes at baseline and 4, 5 or 6 weeks after infection. Some groups were given antibacterial treatment at 4 weeks. RESULTS: An antibody response against Aa occurred within 4 weeks of infection, and 78% of inoculated rats had detectable Aa in the oral cavity (p < 0.05). Aa infection significantly increased loss of attachment that was reversed by antibacterial treatment (p < 0.05). TNF-α expression in the junctional epithelium followed the same pattern. Aa stimulated high osteoclast formation and TNF-α expression in the connective tissue (p < 0.05). PMN recruitment significantly increased after Aa infection (p < 0.05). Aa also increased the number of CD8(+) T cells (p < 0.05), but not CD4(+) T cells or regulatory T cells (Tregs) (p > 0.05). CONCLUSION: Aa infection stimulated a local response that increased numbers of PMNs and TNF-α expression in the junctional epithelium and loss of attachment. Both TNF-α expression in JE and loss of attachment was reversed by antibiotic treatment. Aa infection also increased TNF-α in the connective tissue, osteoclast numbers and CD8(+) T cells in lymph nodes. The results link Aa infection with important characteristics of periodontal destruction.