Cellular responses of the mouse to the peptidoglycan of a gram-positive bacterium (Streptococcus pyogenes).

The cellular responses and the stimulation of the reticulo-macrophagic system induced in the mouse by a purified bacterial peptidoglycan (PGL) as previously described, were studied by the changes in the peritoneal cytology, the macrophage-migration-inhibition test and the clearance of colloidal carbon. PGL was submitted to chemical and immunochemical characterization and was shown to be substantially free of contamination by polysaccharides, phospholipids, teichoic acid and nucleic acids, but to contain a detectable amount of peptide contaminants; N-acetylglucosamine and the tetrapeptide (with terminal D-alanine) were shown to be the main antigenic determinants. This substance had no action on polymorphonuclear leucocytes but induced an inhibition of the migration of macrophages. This was due to an immunological reaction rather than to direct cytotoxicity, as shown by the negative cytotoxicity tests and the age and life-environment-dependence of the phenomenon. The reticulomacrophagic system was significantly stimulated after primary inoculation, and still more so after a booster. The possible mechanisms of these activities, which are therefore independent from toxic and/or inflammatory responses, are discussed.