Antibody formation in mouse bone marrow. V. The response to the thymus-independent antigen Ecsherichia coli lipopolysaccharide.

The occurrence of plaque-forming cells (PFC) in mouse bone marrow was studied during primary and secondary responses to the thymus-independent antigen Escherichia coli lipopolysaccharide (LPS). Anti-LPS responses were induced by various doses of LPS. During the primary response, doses of 1 and 10 mug LPS intravenously (i.v.) were found to evoke a distinct PFC response in both spleen and bone marrow. The spleen contained the majority of PFC until about 5 days after immunization. During the course of the reaction the number of PFC in the bone marrow rose to a level which equalled or surpassed the level in the spleen. LPS doses of 0-001, 0-01 and 0-1 mug i.v. only induced a PFC response in the spleen. Apparently there is a minimal threshold dose of LPS of about 1 mug for PFC to appear in the bone marrow. The secondary response was studied in mice primed with 1 mug LPS i.v. and boosted with either 0-001, 0-1 or 10 mug LPS i.v. 3 months later. After each dose tested the PFC activity in the spleen was several times higher than during the primary response. As was observed in the primary response doses of 0-001 and 0-1 mug LPS i.v. did not evoke a PFC response in the bone marrow. After boosting with 10 mug of LPS i.v. a significant PFC response was found in spleen, bone marrow, thymus, lymph nodes, Peyer's patches and blood. From about 5 days after the booster injection the number of PFC in the bone marrow exceeded the total number found in all other lymphoid organs. The results are discussed in relation to the bone marrow PFC response to the thymus-dependent antigen sheep red blood cells. To this antigen a clear PFC response in the bone marrow is found only during the secondary response.