Peptidoglycan from the potentially pathogenic oral bacterium Actinomyces viscosus is a B-cell mitogen

Cell walls and peptidoglycan from Actinomyces viscosus, strain M-100 were compared for their ability to act as mitogens with spleen cells from germ-free Fischer rats. The cell walls were prepared from trypticase soy broth grown whole cells using a French press, followed by two consecutive washes with 0.1 M tris-HCl buffer, pH 8.0, 1 M NaCl and distilled water. Peptidoglycan was prepared from cell walls by three consecutive formamide extractions at 165 degrees C. On a dry-weight basis, the peptidoglycan was a significantly-better mitogen than cell walls, suggesting that the peptidoglycan is the major mitogenic component of A. viscosus cell walls. Mononuclear spleen cells were separated on a Nylon-wool column into a non-adherent subpopulation enriched for T lymphocytes and a weakly-adherent, plunger-removable subpopulation enriched for B lymphocytes. The non-adherent T-cell subpopulation responded strongly to the T-cell mitogen PHA, but was unresponsive to both the peptidoglycan and cell walls from A. viscosus. In contrast, the weakly-adherent enriched B-cell subpopulation was less responsive to PHA, but was strongly stimulated by A. viscosus peptidoglycan and cell walls. These results indicate that peptidoglycan and cell walls from A. viscosus are B-cell mitogens.