Antibodies to core lipid fractions of endotoxin in children with rheumatic disease.

The titer of IgG and IgM antibodies to two fragments of endotoxin derived from Salmonella minnesota R 595, lipid A width a 2-keto-3-deoxyoctanate oliosaccharide (KDO lipid A), and monophosphoryl lipid A (mono-P lipid), were measured in normal children, children with cystic fibrosis, and children with SLE and all forms of chronic juvenile arthritis. Elevated titers of IgM anti mono-P lipid A were found in all of the rheumatic diseases, but not in cystic fibrosis. The elevated IgM titers were not correlated with concentration of activation fragments of C3 or C4, but IgG anti mono-P lipid A titers, even though not usually elevated, did correlate with C3a and C3d concentrations. The elevated IgM titers to mono-P lipid A may represent a genetically determined hyper-reactivity to normal gastrointestinal antigens, an increased antigenic stimulus from the intestinal tract, or polyspecificity of an antibody of undetermined primary reactivity.