The soluble sonicated extract (SE) from Actinobacillus actinomycetemcomitans inhibited primary T cell-dependent antibody responses in vivo. The production of IgG and IgM to sheep red blood cells (SRBC) was depressed when mice were treated with high concentrations of SE plus SRBC. Preinjection of SE 3 days prior to SRBC completely inhibited IgG production. SE plus SRBC-primed mice showed markedly depressed CD4/CD8 ratios relative to phosphate-buffered saline plus SRBC- or SRBC-immunized mice. SE-sensitized mice showed low blastogenic activity to concanavalin A (Con A) depending on sensitized periods induced by SE. This inhibitory mechanism was, in part, clarified by a suppression of IL-2 synthesis, IL-2 receptor expression and IL-6 secretion by the splenic T cells stimulated with Con A. These results support the hypothesis that the severe infection of A. actinomycetemcomitans suppresses the immune response by affecting CD4/CD8 ratios, followed by lymphokine production and finally antibody responses.

The mechanisms of immune reaction were studied by observations of antigen transition, antibody producing cells, antibody titers and factors affecting them following the transtracheobronchial inoculation of antigens. Results were obtained as follow: Using immuno fluorescence method, intake of labeled antigen was confirmed in alveolar wall and also antibody containing cells were observed.Higher antibody titers and higher IgA levels were confirmed in serum and washing fluid of airway by the transtracheo-bronchial inoculation of antigen than by subcutaneous injection. Additionally, similar studies were performed following the exposure to irritant gases and subcutaneous injection of the immuno-suppressive drugs and some effects were revealed on antibody titers, IgA levels and antibody containing cells.