Antibodies to lipid A: occurrence in humans.

Lipid A, the toxic part of the bacterial endotoxin, is a common antigen for many gram-negative bacteria. Antibodies to lipid A occur naturally in humans; they have been found in 10%-34%, and even up to 73%, of individuals tested, as detected by indirect hemolysis and enzyme-linked immunosorbent assay (ELISA), respectively. Inflammatory bowel diseases (Crohn's disease or ulcerative colitis) cause changes in the level of antibodies to lipid A, as compared with that found in healthy control subjects. Increased levels of antibodies to lipid A are seen in both children and adults with infections due to gram-negative bacteria, such as urinary tract infections (UTI). The highest titers of IgG in serum, as detected by ELISA, have been recorded in patients with development or progression of renal scarring associated with UTI. Since lipid A may play a role in the pathogenesis of renal impairment, the determination of the level of antibodies to lipid A may help in the diagnosis of certain forms of UTI. Possible beneficial roles of antibodies to lipid A during septicemia caused by gram-negative bacteria in humans are still unclear.