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Role for endotoxin in the leukocyte infiltration accompanying Escherichia coli inflammation
Abstract:
Escherichia coli organisms induce polymorphonuclear leukocyte (PMNL) infiltration during clinical infection and also in a rabbit dermal model of inflammation. We investigated the factors which may mediate this host response to E. coli. In vitro incubation of Formalin-killed E. coli in heat-inactivated rabbit plasma or balanced salt solution generated in the supernatant factors which induced in vivo PMNL infiltration upon intradermal injection into rabbits. However, these supernatants, in the presence or absence of plasma, did not induce PMNL migration in vitro. The in vivo activity was stable at 100 degrees C and of high molecular weight (30,000). Antiserum to O antigen or to core glycolipid, but not to K or H antigen, as well as polymyxin B inhibited the release or activity of these E. coli-derived factors. The intradermal injection of 0.02 to 0.2 mug of four different endotoxin preparations or lipid A also induced marked PMNL infiltration in vivo. However, these preparations did not stimulate PMNL migration in vitro and failed to generate chemotactic activity in plasma except at very high concentrations (500 mug/ml). Anti-O serum inhibited PMNL infiltration induced by endotoxins with the corresponding O antigen and anti-core glycolipid serum inhibited all four endotoxins tested, whereas polymyxin B inhibited the activity of the endotoxins as well as that of lipid A. Base hydrolysis of endotoxin abolished PMNL infiltration. It is concluded that (i) endotoxin shed from E. coli (killed or live) may be one factor mediating the PMNL infiltration induced by this organism, (ii) endotoxin probably acts independent of in vivo complement activation, (iii) the activity is dependent on the lipid A moiety, and (iv) antibody binding to O or core glycolipid antigens can modify endotoxin so as to diminish its capacity to induce PMNL infiltration in vivo.
Insights
Escherichia coli releases factors, primarily endotoxin, that attract polymorphonuclear leukocytes (PMNLs) in vivo. This inflammatory response is mediated by the lipid A component and can be reduced by antibodies targeting O or core glycolipid antigens.
Area of Science:
- Immunology
- Microbiology
- Inflammation Research
Background:
- Escherichia coli (E. coli) infection triggers polymorphonuclear leukocyte (PMNL) infiltration.
- Understanding the host response mechanisms to E. coli is crucial for managing infections.
Purpose of the Study:
- To identify factors from E. coli responsible for inducing PMNL infiltration.
- To elucidate the role of endotoxin and its components in mediating this inflammatory response.
Main Methods:
- In vitro incubation of killed E. coli to generate supernatant factors.
- Intradermal injection of factors into rabbits to assess in vivo PMNL infiltration.
- In vitro PMNL migration assays.
- Testing the effects of heat, molecular weight, specific antisera (O, K, H, core glycolipid), polymyxin B, lipid A, and base hydrolysis on E. coli-derived factors and endotoxins.
Main Results:
- Supernatants from killed E. coli induced in vivo PMNL infiltration but not in vitro migration.
- The active factor was heat-stable, high molecular weight, and sensitive to anti-O, anti-core glycolipid, and polymyxin B.
- E. coli endotoxin and lipid A induced significant in vivo PMNL infiltration, dependent on the lipid A moiety.
- Antibodies against O or core glycolipid antigens reduced endotoxin-induced PMNL infiltration.
Conclusions:
- Endotoxin shed from E. coli is a key mediator of PMNL infiltration.
- Endotoxin's activity appears independent of complement activation.
- The lipid A component is essential for endotoxin's inflammatory activity.
- Antibody binding to O or core glycolipid antigens can attenuate the inflammatory capacity of endotoxin.