Polyclonal B-cell response to stimulation with Escherichia coli lipopolysaccharide in dietary protein restriction

The polyclonal B-cell response to Escherichia coli lipopolysaccharide was studied in C57BL/6 mice maintained after weaning on either a moderate protein-restricted diet with 8% casein or a normal diet. After in vitro or in vivo stimulation with the endotoxin, autoreactive and anti-hapten antibody-producing cells were quantitated by direct plaque assay, using bromelain-treated mouse erythrocytes and trinitrophenylated sheep erythrocytes as targets. Larger numbers of plaque-forming cells were generated in cultures of spleen cells from dietary-restricted than from normal mice stimulated with various doses of lipopolysaccharide. The number of background plaque-forming cells was also higher in nonstimulated spleen cell cultures from restricted animals. After injection of lipopolysaccharide in vivo, the number of cells producing antibodies to bromelain-treated mouse erythrocytes per 10(7) spleen cells was significantly increased in dietary-deficient mice. The results are discussed in relation to the different sensitivities of lymphocyte populations to protein deficiency and to the possible presence of high levels of endogenous polyclonal B-cell activators in the restricted mice.