Extracellular proteinaceous substances from Haemophilus actinomycetemcomitans induce mitogenic responses in murine lymphocytes

An extracellular proteinaceous substance (ES) and lipopolysaccharide (LPS) were prepared from culture supernatants and whole cells of Haemophilus actinomycetemcomitans Y4, respectively. In addition, extracellular LPS (E‐LPS) was isolated from the ES preparation by the phenol‐water procedure. Both the ES and LPS induced Limulus amebocyte lysate clotting and the local Shwartzman reaction. LPS and E‐LPS from the strain were mitogenic for BALB/c, BALB/c (nu/nu) and C3H/HeN mouse spleen cells, but not for C3H/HeJ spleen cells and BALB/c thymocytes. On the other hand, ES was also mitogenic for C3H/HeJ spleen cells. Polymyxin B suppressed to a lesser extent the mitogenicity of ES than that of LPS and E‐LPS. The mitogenicity of ES was markedly inhibited by pronase treatment. These results suggest that H. actinomycetemcomitans produces extracellularly proteinaceous mitogenic substances as well as LPS.