Response of the lymphoid organs of the mouse to the peptidoglycan of a gram-positive bacterium (Streptococcus pyogenes).

The response of the lymphoid organs of the mouse to the injection of a Gram-positive (Streptococcus pyogenes) bacterial peptidoglycan (PGL) has been investigated by several complementary techniques. Special cares were brought to: a) the extraction mode and the characterization of the bacterial fraction, b) the sanitary and microbiological status of the mice, and c) the lack of biologically active contaminants, even at a trace level. In these conditions, the local reaction at the site of inoculation was very moderate, transient and not very distinctive. No toxic reactions were observed, even with doses of several milligrams per mouse. Changes in lymphoid organs, as determined by changes in weight, incorporation of radioactive precursors and detailed histological study revealed that PGL did not induce the typical responses of ordinary antigens. Changes in the weight of organs were not significant and there was no dose-response relationship. In the lymph node, the response was confined to the paracortical area; the lymphocyte activation stood at an early stage and became characterized only after booster injection. There was no activation of antibody-producing cells. An important recruitment of active macrophages was observed; this could participate to the adjuvant activity of PGL, whose at least a part of the biological activity is therefore independent of the inflammatory and/or toxic response.