STUDIES ON LIPID A IMMUNITY IN ANIMALS AND INFECTED CHILDREN

ABSTRACT Enzyme-linked immunosorbent assay (ELISA) was applied for antibody determination against lipid A. It was found to be more sensitive than the generally used indirect hemolysis (IH) or indirect hemagglutination (IHA). ELISA was also used to study exposure of lipid A on E.coli bacteria as well as in crude antigen preparations. Lipid A was only available in all four crude antigen preparations made from rough E.coli . Anti-lipid A antibody production was investigated in immunized animals. Animal immunized with lipid A conjugated to bacteria or erythrocytes in general gave an antibody response, in contrast to rabbits immunized with bacteria. Anti-lipid A antibodies were also analyzed in healthy children and adults, adults with inflammatory bowel disease, IBD (Ulcerative colitis or Mb Crohn), or girls with urinary tract infection (UTI). Antibodies of both IgG and IgM class were found in children and adults. The frequency of IgG antibodies to lipid A was lower in patients with a great extension of their IBD as compared with healthy adults. Children with acute pyelonephritis, cystitis or asymptomatic bacteriuria had higher IgG antibody titres compared to healthy children. Especially high IgG titres were found in patients with progressive kidney damage caused by pyelonephritis. Similar results were observed in infected rats with pyelonephritis. Intraperitoneally injected antiserum to lipid A did not protect rats against experimentally induced pyelonephritis. In conclusion, lipid A seemed not to be available on the intact bacteria but in the material released from the bacteria. The availability of the antigenic lipid A structure was higher in antigen preparations from rough bacteria defect in the lipopolysaccharide synthesis than in smooth bacteria. Infection caused by gram-negative bacteria in the urinary tract induced anti-lipid A antibody production although no protection with anti-lipid A serum was afforded against pyelonephritis. Determination of anti-lipid A antibodies might reveal progressive kidney damage in individuals with acute pyelonephritis.