[Mechanism of stimulation of spleen mononuclear cells by gram-positive bacterial peptidoglycan].

Periodontal disease is a chlonic inflammatory disorder, and for which oral microbes are supposed to be responsible. Among oral microbials, gram-negative bacterias have been studied extensively in relation to periodontal disease for their pathogenicity due to their lipopolysaccharide (LPS), exocellular enzymes or bacterial toxin. As for gram-positive bacterials, it has been reported recently that gram-positive bacteria can elicit immunological responses, and this may be responsible for the initiation and/or development of periodontal disease. However, precise mechanisms of bacterial action, especially of gram-positive bacteria, on periodontal disease have not been elucidated yet. In this experiment, therefore, gram-positive bacteria (S. epidermidis), peptidoglycan subunits of S. epidermidis (SEPS) and muramyl dipeptide (MDP) were used to investigate for their activities to stimulate spleen mononuclear cells to replicate and produce various kinds of cytokines. Immunological responsibilities of various strains of mice were explored to investigate the difference of defence of mechanisms. Following results were obtained. (1) S. epidermidis itself showed a extremely low cell-mediated activity to stimulate the replication of spleen mononuclear cells in contrast to E. coli. Staphylococcal phage lysate and SEPS stimulated remarkally the replication of spleen mononuclear cells. (2) The stimulation of spleen mononuclear cells was accompanied by the production of interleukin 3 (IL-3) and colony stimulating factor (CSF), but interleukin 2(IL-2) was not produced as in the case of E. coli. (3) Analysis of cell surface antigens revealed the increase of the numbers of Ia+ and Mac-2+ bone marrow cells following stimulation of spleen mononuclear cells with SEPS. However, T or B cells were not increased. (4) Macrophage-depleted and antisera Ia-treated spleen mononuclear cells showed a marked decrease of replicating activity of spleen mononuclear cells. (5) Among the various strains of mice tested C3H/HeN, Balb/c, AKR, DBA/2, C57BL/6, ddY, C3H/HeJ, MRL/lpr and showed a high immunological responses, but Balb/c did not. C3C/HeJ and MRL/lpr also lacked immunological reactivity. These results suggest that proliferative response of lymphocyte with peptidoglycan in gram-positive bacterium is very important for infection and its defensive reaction against gram-positive bacteria.