Ten µg. of the lipopolysaccharide endotoxin of Salmonella typhosa was given to rabbits intravenously to enhance the subsequent antibody response to an unrelated substance. The spleens were removed 24 hours later, diced, and incubated 1 hour with the antigen, bovine-γ-globulin (BGG), in a protein-free medium. After washing, the tissues either were extracted at once or planted and the fluids and tissues harvested 1 to 3 days later. Antibody was determined by a modification of the Boyden hemagglutination technique.
Small amounts of antibody were synthesized as early as 1 hour after the addition of antigen. The antibody formed could be specifically inhibited with BGG, was not dialyzable, and did not sediment at 105,000 g for 2 hours.
Dose-response studies revealed no antibody formation when the BGG concentration was 0.005 or 0.05 mg./ml. The best responses were obtained at concentrations of 0.5 to 5.0 mg./ml. These results were found irrespective of whether the animal had previously received BGG in vivo.
Forty per cent autologous serum increased antibody formation about 9-fold over that secured with protein-free medium or with 40 per cent homologous serum. Antibody formed with this system could be detected by 50 per cent complement fixation test, although at much lower titer than found by hemagglutination.
While spleens from rabbits previously given BGG did not produce more antibody than spleens from normal rabbits, they differed in that they produced antibody without the involvement of endotoxin.
Under appropriate circumstances, endotoxin was effective in vitro in enabling spleen fragments to produce antibody to BGG.
Cortisone acetate administered to rabbits prior to the removal of the spleen severely inhibited antibody production in vitro. Sodium prednisolone phosphate added in vitro showed a similar irreversible effect at concentrations as low as 2 x 10–5 M. Nitrogen mustard inhibited antibody formation at concentrations as low as 10–4 M.