Prevention of endotoxin-induced abortion by treatment of mice with antisera

Small amounts of bacterial lipopolysaccharides (LPS), usually extracted from smooth organisms, have previously been shown to interrupt pregnancy in mice. The findings reported here demonstrate that LPS obtained from rough bacterial strains were also abortifacient. Moreover, lipid A, which represents a common toxic structure of LPS in many species of gram-negative Enterobacteriaceae, had the same activity, whereas the nontoxic polysaccharide moiety did not affect pregnancy. Our data also showed that specific bacterial antisera raised in various animal species protected pregnant mice from the abortifacient effect of smooth or rough LPS, and that this activity disappeared after absorption of the antisera with homologous bacteria. Nevertheless, antibodies to lipid A protected pregnant female mice challenged with lipid A or even with LPS extracted from various organisms. Moreover, pregnant mice treated with both antiserum and an antiserotonin compound were protected more effectively against LPS-induced abortion than mice treated with either substance alone.