Endotoxin-induced auto-immunity in mice. II. Reactivity of LPS-hyporesponsive and C5-deficient animals

Auto-antibody responses and circulating immune complex levels of mice with abnormal reactions to endotoxin were investigated after injection with the bacterial product. It was observed that C3H/HeJ mice displayed very high background plaque-forming cell responses towards bromelain-treated isologous erythrocytes which were slightly enhanced by endotoxin treatment. The same animals, however, did not bear autohaemolysins in their serum, but became so upon endotoxin injection. A possible relationship between the high background reactivity of C3H/HeJ mice and the low toxicity of endotoxin in these animals is discussed. Neither untreated nor lipopolysaccharide-injected C3H/HeJ mice showed significant immune complex levels in their sera. This may be explained by their hyporesponsiveness, but by a low sensitivity to the toxic effects of endotoxin as well. C5-deficient and C5-sufficient mice showed similar auto-immune reactions, indicating that C5a, which is responsible for other effects of endotoxin, is not involved in endotoxin-induced auto-immunity.