Immunochemical study of a bacterial endotoxin: Shigella flexneri type Z.

The endotoxins of the Gram-negative bacteria have similar biological and chemical properties. The toxic antigen of Shigella flexneri Type Z was selected as a representative endotoxin, and it was confirmed that the antigen consists of a polysaccharide conjugated with phospholipid and protein. By the technique of zone electrophoresis, the polysaccharide of the purified endotoxin was shown to be conjugated with each of three different proteins, and each conjugate proved toxic and antigenic for the rabbit. Two of the protein conjugates were digested by trypsin and the released polysaccharide appeared to conjugate with the remaining trypsin-resistant protein. Immunological analysis revealed that the purified toxic antigen is heterogeneous and that the polysaccharide and protein components possessed serological activity. The trypsin-treated toxin had a single electrophoretic zone and its precipitation in gel suggested immunological purity. Proteolytic treatment of the endotoxin did not destroy its toxicity or antigenicity for the rabbit.