Inhibition of Lipid A- and Lipopolysaccharide-Induced Cytokine Secretion, B Cell Mitogenesis, and Lethal Shock by Lipid A-Specific Murine Monoclonal Antibodies

Three murine hybridomas secreting IgM monoclonal antibodies (MAbs) to lipid A (LA) of Salmonella minnesota R595 were generated. These MAbs serologically cross-reacted with LA and lipopolysaccharide (LPS) ofunrelated gram-negative bacterial species. All three MAbs significantly suppressed the ability of LA and LPS from various gram-negative bacteria to induce tumor necrosis factor (TNF)-α (36%-67%) and interleukin-1 (30%-98%) in murine peritoneal macrophages and to stimulate B lymphocytes (37%-78%). Lipid A-induced TNFα production was also suppressed in mice (86%-88%). All three antibodies protected adrenalectomized mice against lethal shock induced by LA ofS. minnesota R595. Optimal protection was achieved with one of the antibodies (MLA-1), if it was administered 2 h before injection of lipid A, and full protection persisted ⩽24 h. Moreover, MLA-1 was able to protect adrenalized or D(+)-galactosamine- sensitized mice against lethal shock induced by LPS derived from various gram-negative bacteria. This cross-protection could be predicted on the basis of serologic cross-reactivity and cross-neutralization by MLA-1 of the bioactivity of the heterologous LA or LPS in vitro.