The effect of endotoxin or lipopolysaccharide (LPS) on tolerance induction in bone marrowderived lymphoid cells (B cells) was investigated.Dinitrophenylated amino acid copolymer-L-(glutamic acid, lysine) (DNP-GL) acts as a potent tolerogen on normal and DNP-primed B cells. LPS significantly enhanced the anti-sheep red blood cell plaque-forming cell (anti-SRBC PFC) response that occurred after the immunization with a low dose of SRBC. LPS did not induce the primary anti-DNP PFC response after the injection of DNP-GL, nor did it prevent the tolerance induction in normal and DNP-primed B cells that occurred after the administration of DNP-GL.It is well known that bacterial endotoxin or lipopolysaccharide (LPS) enhances a humoral immune response. Several findings indicate that the adjuvant effect is caused by direct stimulation to bone marrowderived lymphoid cells (B cells) by LPS : a) LPS induces an antibody response to an immunizing antigen in circumstances where the effects of thymus derived lymphoid cells (helper T cells) are supposed to be absent or limited [15,21,28,29,36] ; b) LPS prevents tolerance induction in B cells [19,24] ; c) responsiveness of mice to the mitogenic and adjuvant activities of LPS seems to be controlled by a single gene [30,31,35]. Several results that are not compatible with this interpretation have been reported, however [3,10,32]. To explain these discrepancies, it seems necessary to investigate more fully the precise mechanism of the adjuvant effect of LPS.The present study was undertaken to determine the effect of LPS on the tolerance induction in B cells specific for DNP that occurred after the administration of a potent tolerogen. As a tolerogen, we used dinitrophenylated amino acid copolymer-L-(glutamic acid, lysine) (DNP-GL). The results obtained indicate that LPS does not induce the primary anti-DNP antibody response after the injection of DNP-GL, nor does it prevent the tolerance induction in normal and DNP-primed B cells that occurred after the administration of DNP-GL.
MATERIALS AND METHODSAnimals. C57BL/6 mice, male, were bred in