Relationship of structure and biological activity of bacterial endotoxins

TLDR: A picture of endotoxin structure with rather vague contours and some light about its mode of action emerges from the many years of study, and the overall seems to be similar in several gram-negative strains.

Abstract: There are two factors which must be borne in mind before we start the discussion of the chemistry and biology of endotoxic bacterial lipopolysaccharides (LPS). The iirst is that the information available is limited to individual strains. I t is clear that different bacterial strains produce chemically dissimilar polysaccharides. There is some evidence which indicates that other parts of the LPS molecule, such as the lipid moiety, are not entirely identical in all strains either, and there is no reason to assume that they should be identical in their chemical composition, no mat ter how desirable this would be to us chemists. The only feature which seems to be shared by most gram-negative endotoxins is the /ascinating array o/ biological activities. But here again we cannot speak about identity, since some data Jn the literature can be interpreted as evidence for different degrees of activity in one or another biological parameter. Whether these are real differences or only apparent ones due to poor reproducibility in the measurement of different biological activities remains an open question. Nevertheless, generalizations about the structure or the biological activity of endotoxins should be avoided. Another even more disturbing factor we have to realize is the heterogeneity of endotoxic LPS preparations. I t has been detected that all endotoxic LPS preparations investigated thus far consist of a number of components. These materials are similar but still different in their chemical composition and they elicit different biological activities if injected into experimental animals. A review of the aspects of chemical and biological heterogeneity of endotoxins is in press [1]. Despite these factors, a picture of endotoxin structure with rather vague contours and some light about its mode of action emerges from the many years of study, and the overall pat tern seems to be similar in several gram-negative strains. Heterogeneity as well as individual variations from strain to strain may be restricted to certain features or smaller details of the architecture which may have limited bearing on the most characteristic structural or biological properties of all endotoxins. Although our knowledge of the