Search

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 cyclostomes 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 [tmoles/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 phylogenetically between hagfish and shark.

Functional separation of the two signals involved in stimulating immunological responses was achieved through the judicious use of two natural bacterial antigens. Native protoplasmic polysaccharide (NPP) extracted from Escherichia coli was immunochemically identical to the lipopolysaccharide (LPS) extracted from the same organism. However, NPP was not endotoxic, not mitogenic, did not fix complement, and was immunologically independent of T cells. The NPP, which appeared to contain only the antigenic signal, could induce a primary antibody response in mice and could sensitize mice for a secondary response. However, the antigenic signal contained in NPP was insufficient to trigger a secondary response in mice primed with either NPP or LPS. LPS, containing both the antigenic and second signals, was required to trigger a secondary response in primed mice.