Interactions of the Complement System with Native and Chemically Modified Endotoxins

Abstract

Endotoxic lipopolysaccharides (LPS) isolated from Serratia marcescens, Veillonella alcalescens, and Salmonella typhosa were potent in their ability to induce fixation of complement (C') in normal guinea pig, rabbit, mouse, and human serum. The C'-fixing ability of LPS was pronounced even when assays were performed in undiluted serum, and was lost after each of four chemical modifications which resulted in loss of biological toxicities. The detoxification procedures had in common the cleavage of ester-bound, long-chain carboxylic acids. The ability of biologically active LPS to fix C' in normal guinea pig serum was reflected chiefly in dramatic uptake of classical C'3 (C'3t); fixation of C'1, C'4, and C'2 was virtually undetectable. Hence, it was the capacity for fixation of C'3t which was lost most overtly during detoxification. Addition of immune serum to the assay mixtures resulted in detectable fixation of C'1 and C'4. Biologically active LPS also fixed more of these components than did detoxified LPS. Immune serum restored the ability of detoxified LPS to fix C'3t, but whether this is by the original pathway is not yet clear. We concluded that the loss of certain biological activities and the loss of ability to fix C'3t in normal serum after LPS detoxification involved loss or rearrangement of substrates on LPS which either initiated or supported, or both, its interaction with the complement system. It was apparent that the ability to fix C' can serve as a valuable in vitro indicator of the integrity of the toxic conformation of biologically active LPS membrane fragments. These experiments supported the hypothesis that certain of the biological activities induced by endotoxins are mediated via the complement system.

Interactions of the Complement System With Endotoxic Lipopolysaccharide: Consumption of Each of the Six Terminal Complement Components

“…Given amounts of LPS consumed greater quantities of the C'3-C'9 components than did immune complexes or AHGG, even though they consumed much smaller quantities of the earlier-acting C' components. Such a relatively "preferential" consumption of classical C~3 during serum-polysaccharide (20) and serum-lipopolysaccharide interactions (2,3,7,8) had previously been observed, as had relatively preferential consumption of the earlier-acting C' components during incubations of serum with preformed immune complexes and AHGG (2,3,8,(20)(21)(22)(23).…”

“…Previous investigations have shown that endotoxic LPS fixes large amounts of classical C'3 during incubation with guinea pig serum, despite minimal consumption of CI1, C'4, and C'2 (2,3). Classical C'3 now is known to consist of at least six separate proteins (9)(10)(11).…”

“…(Received for publication 20 June 1968) When endotoxic lipopolysaccharides (LPS) are incubated with fresh guinea pig serum, a strong interaction between LPS and the complement (C') system ensues. C' is "fixed" or consumed (2,3) while lesions which relate to the activity of the terminal C' components (4, 5) appear on LPS (2, 6.) In this interaction pronounced consumption of the classical terminal C' component (C'3) is observed, despite only minimal consumption of the earlier-acting C'I, C'4, and C'2) (2,3,7,8).…”

“…C' is "fixed" or consumed (2,3) while lesions which relate to the activity of the terminal C' components (4, 5) appear on LPS (2, 6.) In this interaction pronounced consumption of the classical terminal C' component (C'3) is observed, despite only minimal consumption of the earlier-acting C'I, C'4, and C'2) (2,3,7,8). The classical C'3 activity (hereafter referred to as "C~3-C'9 '') is now known to consist of at least six discrete proteins, termed C'3, C'5, C%, C'7, C'8, and C'9 (9)(10)(11).…”

Serum-Dependent Phagocytosis of Paraffin Oil Emulsified With Bacterial Lipopolysaccharide

“…The way in which lipopolysaccharide particles initiate properdin activation is not known, although the importance of primary structure for the biologic activity of lipopolysaccharide has been illuminated by studies in which chemical modifications of lipopolysaccharide resulted in loss or diminution in endotoxic potency. Diverse treatments, such as acetylation (30), alkaline hydrolysis (43), and deacylation (31), have been shown to diminish mouse lethality and complementconverting ability of lipopolysaccharide without destroying antigenicity. Such treatment also appears to compromise the capacity of lipopolysaccharide to activate the properdin system.…”