The capacity and mechanism of bone marrow antibody formation by thymus-independent antigens.

Primary immunization of mice with certain thymus-independent (TI) antigens (i.e., TNP-LPS and DNP-Ficoll) leads to antibody formation in the bone marrow (BM). TNP-Brucella abortus, Pneumococcus pneumoniae organisms, and alpha-(1,6) dextran, on the other hand, do not induce a BM antibody-producing plaque-forming cell (PFC) response. This paper deals with the mechanism underlying antibody formation in the BM to TNP-LPS and DNP-Ficoll. The majority of the BM-localizing PFC induced by TNP-LPS are formed within the BM from the proliferating lymphocyte pool, because this response was found to be resistant to splenectomy and sensitive to treatment with hydroxyurea (HU) before immunization. This local activation of newly formed B cells requires in addition to the antigenic signal of TNP-LPS the mitogenic signal from the lipid A component of LPS. In contrast, the BM PFC response to DNP-ficoll was reduced in splenectomized mice and resistant to HU treatment before the primary immunization. Thus, antibody formation in the BM to DNP-Ficoll is mainly dependent on long-lived B cells that migrate from the peripheral lymphoid organs into the BM.