Inhibitory effects of rabbit antisera on mitogenic activity of Actinobacillus actinomycetemcomitans lipopolysaccharide.

Lipopolysaccharides (LPSs) were isolated from Actinobacillus actinomycetemcomitans strains ATCC 29523 (serotype a), Y4 (b), and NCTC 9710 (c) by the hot phenol-water procedure. Y4 lipid A was obtained by the hydrolysis of Y4 LPS in 1% acetic acid. All the LPS preparations and Y4 lipid A were mitogenic for C3H/HeN mouse spleen cells, but not for C3H/HeJ mouse spleen cells. Immunoglobulin preparations partially purified by ammonium sulfate precipitation at 33% saturation from rabbit antisera against Y4 whole cells inhibited the mitogenic response of C3H/HeN mouse spleen cells to LPSs from all the strains of A. actinomycetemcomitans and Y4 lipid A. Anti-Y4 LPS immunoglobulin preparation inhibited the mitogenic activity of Y4 LPS and Y4 lipid A. Furthermore, anti-Y4 whole cell Fab fragments inhibited the mitogenic activity of both Y4 LPS and Y4 lipid A. These results suggest that antibodies against A. actinomycetemcomitans LPS may modify immune responses of lymphocytes to this organism at periodontal sites.