Protective effects of anti-O polysaccharide and anti-lipid A monoclonal antibodies on pulmonary hemodynamics.

Monoclonal antibodies (MAbs) directed to endotoxin can protect in some animal models against the pathophysiological effects of endotoxin infusion. When 0.02 microgram/kg of lipopolysaccharide (LPS) derived from Escherichia coli O111:B4 was incubated in vitro for 2 h with the murine immunoglobulin G MAb, 5B10, directed against the O-polysaccharide antigenic domain of E. coli O111:B4 and then the mixture was infused into sheep, we noted significant protection. The second temperature peak was decreased (P < 0.05 vs. LPS control). The acute pulmonary arterial pressure elevation was diminished (mean peak pulmonary arterial pressure 23.2 +/- 2.5 mmHg, P < 0.05 vs. LPS control), and the peak plasma thromboxane B2 level was reduced (mean peak thromboxane B2 level 0.50 +/- 0.15 ng/ml, P < 0.05 vs. LPS control). In contrast, preincubation of the LPS with a human immunoglobulin M MAb, HA-1A, directed against the core glycolipid of the LPS molecule provided no protective effects in this sheep model. This finding is in agreement with recent studies reporting HA-1A may bind to antibiotic-treated bacteria but not to purified smooth LPS.