<i>Actinobacillus actinomycetemcomitans</i> mitogenicity for B cells can be attributed to lipopolysaccharide

Abstract

The purpose of this investigation was to determine the component(s) of whole Actinobacillus actinomycetemcomitans bacteria responsible for B cell mitogenic activity. Congenitally athymic “nude” rats were used as a source of B cells devoid of T lymphocyte activity. Spleen cells were cultured with, or without, whole formalin‐killed A. actinomycetemcomitans bacteria or with purified LPS from A. actinomycetemcomitans. Dose‐response curves to A. actinomycetemcomitans cells or to A. actinomycetemcomitans ‐LPS showed that responses were dose dependent. If optimal quantities of both A. actinomycetemcomitans and A. actinomycetemcomitans ‐LPS were added in combination, the proliferative responses were the same as if either was added alone, i.e., the responses were not additive. Polymyxin B at 2μg/well completely abrogated the proliferative response of athymic rat splenocytes to 10 7 A. actinomycetemcomitans cells or to 1.25 μg A. actinomycetemcomitans ‐LPS/well. Therefore, the in vitro early proliferative response of B cells to A. actinomycetemcomitans can be attributed to the presence of LPS on A. actinomycetemcomitans cells. A considerable portion of the in situ lymphocytic gingival response to A. actinomycetemcomitans infection seen in periodontal disease patients may be a B cell mitogenic response to the LPS of this bacterium.