Bacterial endotoxin (lipopolysaccharide) as a cause of erythema multiforme.

The classic iris lesions in a patient with erythema multiforme bullosum were reproduced grossly as well as microscopically by the intradermal injection of a variety of heat-killed, Gram-negative bacteria, as well as their common endotoxin, lipopolysaccharide W. In vitro exposure of the patient's blood to these antigens induced specific fibrin microclots characteristic of a hypersensitivity state. It is possible that some cases of erythema multiforme associated with a variety of respiratory, gastrointestinal, or urinary tract infections may represent a single specific delayed sensitivity reaction to the bacterial endotoxin, lipopolysaccharide.