IgG Antibodies to Gram-negative endotoxin in human sera. I. Lipopolysaccharide (LPS) cross-reactivity due to antibodies to LPS core

A series of 700 blood donor sera were screened for IgG antibodies to the core of Gram-negative bacterial endotoxin with a quantitative enzyme-linked immunosorbent-assay (ELISA), based on a cocktail of incomplete-core R-LPS from four different Gram-negative bacterial species, and further serum samples were obtained from donors exhibiting a range of different reactivity for isolation of serum IgG. Analysis of the different IgG samples by ELISA employing a panel of individual LPS from 31 different Gram-negative bacteria covering a range of species, serotypes and R-LPS chemotyes showed that high-titer sera from the screening ELISA expressed IgG with multiple reactivity to LPS in the complex ELISA. We investigated this multiple reactivity in three serum IgGs by inhibition and absorption of isolated serum IgG ELISA reactivity to R-LPS, employing purified LPS and whole bacteria respectively. In two cases the ELISA reactivity appeared to be predominantly attributable to a single antibody component directed to the inner LPS core structure in the lipid A to KDO region. For the third serum IgG, the results suggested that the cross-reactivity may be attributable to more than one specificity-group of cross-reactive antibodies, although still restricted to the LPS inner core structures.