Reactivity of Antibodies to Core Glycolipid with Gram-Negative Bacteria

Studies of the cross-reactivity of antibodies to core glycolipid with assorted isolated, heterologous lipopolysaccharides (LPSs) confirm the conservation of core glycolipid epitopes among gram-negative bacterial species. However, the accessibility of core glycolipid epitopes to antibody in the intact bacterial cell may be affected by the cell surface structure. In studies with ¹²⁵I-labeled monoclonal antibodies to core glycolipid that cross-react with isolated LPS, the degree to which antibodies can bind to LPS in the outer membrane of intact, viable, gram-negative bacterial cells was found to vary with the strain of bacteria tested. Sequestration of bacterial cell-bound LPS from antibody was confirmed in a smooth strain of Escherichia coli by means of immunoelectron microscopy. The inability of antibody to bind to membrane-bound LPS suggests that such sequestered LPS may also be unable to effect toxicity in the infected host until liberated by bacterial cell breakdown.