Inactivation of Endotoxin by Serum: A Phylogenetic Study

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Abstract
In an attempt to elucidate the nature of the endotoxin-altering reaction, normal sera from animals of different phylogenetic levels were tested for capacity to inactivate endotoxin from Escherichia coli. Inactivation was assayed quantitatively by reduction in capacities of endotoxin to be precipitated by homologous antiserum and to kill mice, and by changes in its immunodiffusion pattern. Sera from species of Mammalia, Aves, Reptilia, Amphibia, Osteichthyes, and Chondrichthyes were shown to have similar capacities to inactivate endotoxin, whereas sera from cycIostomes and hemolymphs from crustaceans altered endotoxin only slightly or not at all. In general, the qualitative nature of the endotoxin-altering reaction by these sera was similar in that the reaction was inhibited by calcium (100 μmoles/ml) and, excepting carp and turtle sera, it was heat stable (56 C for 30 min). Inactivation was greater when endotoxin was incubated with serum at 37 C rather than at 3 C or 26 C. It is postulated that an endotoxin-altering mechanism similar to that of human serum originated phylogenetic ally between hagfish and shark.

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