Chemical structure and biological activity of endotoxins (lipopolysaccharides) and lipid A

Principles of a quantitative assay for bacterial endotoxins in blood that uses Limulus lysate and a chromogenic substrate

Some factors affecting the use of chromogenic substrates with Limulus lysate for assaying bacterial endotoxins in blood have been assessed. It was found that endogenous amidases, which degrade the substrate, could be inactivated by heating serum at 60 degrees C for 15 min. Endotoxin was found not to be removed from serum during clotting. A potent inhibitor of the activated lysate was found to be anti-thrombin II, but specific absorption of anti-thrombin II from plasma reduced only marginally the inhibition of lysate by plasma. The presence of specific antibody to the endotoxin was found not to affect its ability to activate lysate. Inactivation of endotoxin by serum enzymes was biphasic in unheated serum, and most of the activity was destroyed in 3 h at 37 degrees C or in 24 h at 5 degrees C. The relevance of these findings to the objective quantitation of endotoxin activities is discussed.

Endotoxin-induced uveitis in the rat

Experimental studies of ocular inflammation induced by endotoxin have been performed almost exclusively in rabbits. Although the rat has been considered refractory to both the systemic and local effects of endotoxin, the present study has shown that intravitreal injection of endotoxin evoked a characteristic acute inflammatory response which was reproducible and dose-dependent. In addition, a consensual ocular response in the control eye occurred which was less severe but also dose-dependent. Preliminary investigations support the view that consensual responses of this nature may be mediated by a nervous reflex are mechanism. Sequential histological analysis revealed a marked polymorphonuclear cell infiltration of most ocular tissues in the early stages, while mononuclear cells predominated after 3 days. Widespread intravascular microthrombi were also observed, particularly in the ciliary vessels. Recovery, however, was usually complete by 7 days.

Lipid A antiserum-mediated protection against lipopolysaccharide- and lipid A-induced fever and skin necrosis

The antiendotoxic activity of lipid A antiserum was studied in rabbits, using lipid A (lipopolysaccharide)-induced fever and skin necrosis as test systems. It was found that lipid A antiserum had no significant antipyretic effect when it was incubated with lipid A or injected intravenously before lipid A challenge. However, in animals that were pretreated (day 0) with a single dose of lipid A (lipopolysaccharide), a significant protective effect of passively transferred antiserum (day 1) to lipid A (lipopolysaccharide fever) (day 2) was observed. Also, the lipid A (lipopolysaccharide)-induced local shwartzman reaction could be prevented by lipid A antiserum. In the fever system, the degree of protection depended on the preparative and the challenge doses as well as on the amount of antiserum transferred. The fever protection mediated by lipid A antiserum seemed to be lipid A (lipopolysaccharide) specific with regard to both the preparative and the challenge injections. Lipid A specificity of the protective factor present in the antiserum was indicated by the fauggest that the factor might be identical with lipid A-specific immunoglobulin. The significance of the preparative injection is not understood at the present time. Iti is concluded, however, that in the fever protection system described, besides specific humoral factors, other factors, perhaps cellular, are involved.

Mechanisms of endotoxin tolerance. The role of the spleen

Splenectomy markedly impaired the production of circulating anti-endotoxin antibodies during the initial 10 days after .v. administration of a Boivin preparation of Escherichia coli endotoxin (ET) in both rabbit and man. Increase in antibodies with secondary (flocculating and bactericidal) activities were virtually abolished, whereas increases in antibodies with primary (binding) activity were significantly reduced. On the basis of these findings, splenectomized rabbit and man were employed to test the hypothesis that the early phase (less than 72 h) of pyrogenic tolerance to endotoxin is independent of anti-endotoxin antibody but that such antibody contributes significantly to the later phase (less than or equal to 72 h) of tolerance. In the splenectomized rabbit, the initial pyrogenic reponses to ET and the subsequent tolerant responses at 24 and 48 h were comparable to sham-operated controls...