HOST RESPONSES INDUCED BY COINFECTION WITH PORPHYROMONAS-GINGIVALIS AND ACTINOBACILLUS-ACTINOMYCETEMCOMITANS IN A MURINE MODEL

In this study, evidence is presented that mixed infection with the per iodontal pathogens Porphyromonas gingivalis and Actinobacillus actinom ycetemcomitans results in a synergistic effect in their pathogenicity and in their ability to induce humoral and cellular host responses. BA LB/c mice were injected subcutaneously on the back with P. gingivalis ATCC 53977, A. actinomycetemcomitans 75 or a mixture of both bacteria. Samples of blood and fluid from abscesses formed at the site of injec tion (first degree) or distant from the injection site were collected for microbiologic analysis. Serum and spleens were obtained for evalua tion of humoral and cellular responses to P. gingivalis and A actinomy cetemcomitans. Mice injected with A. actino-mycetemcomitans had first- degree lesions only, whereas mice injected with P. gingivalis and A. a ctinomycetemcomitans had lesions at first- and second-degree sites fro m which both bacterial species were isolated. A serum anti-P. gingival is response was induced in P. gingivalis-injected mice, which was high er in mice injected with P. gingivalis and A. actinomycetemcomitans. T his pattern was not seen in the anti-A. actinomycetemcomitans response . Lymphoproliferative responses to phytohemagglutinin, Escherichia col i lipopolysaccharide and P, gingivalis of spleen cells from infected m ice were decreased, especially following co-infection, Furthermore, co -infection of mice resulted in the greatest decrease in the number of CD5(+), especially CD4(+) lymphocytes.