ARTHRITIS & RHEUMATISM Vol. 43, No. 11, November 2000, pp 2583–2589 © 2000, American College of Rheumatology ORAL ANTIBIOTICS AS A NOVEL THERAPY FOR ARTHRITIS Evidence for a Beneficial Effect of Intestinal Escherichia coli EDWARD E. S. NIEUWENHUIS, MAARTEN R. VISSER, ANNEMIEKE KAVELAARS, PIETER M. COBELENS, ANDRE FLEER, WIL HARMSEN, JAN VERHOEF, LOUIS M. A. AKKERMANS, and COBI J. HEIJNEN Objective. The intestinal flora is thought to play an important role in regulation of immune responses. We investigated the effects of changing the intestinal flora on the course of adjuvant-induced arthritis (AIA) and on experimental autoimmune encephalomyelitis (EAE) by the use of oral antibiotics. Methods. Oral treatment with either vancomycin or vancomycin, tobramycin, and colistin was started after AIA and EAE induction. Clinical symptoms of AIA and EAE were monitored, and microbial analysis of ileal samples was performed. Results. Oral vancomycin treatment after disease induction significantly decreased clinical symptoms of AIA. Simultaneously, increased concentrations of Esch- erichia coli were detected in the distal ileum of vancomycin-treated rats. Ileal concentrations of E coli were inversely related to disease scores in rats with AIA. Coadministration of colistin/tobramycin to prevent the increase in E coli abrogated the beneficial effect of vancomycin on AIA. Vancomycin treatment also reduced the clinical symptoms of EAE. Conclusion. We propose oral vancomycin as a novel therapeutic strategy in autoimmune diseases. Nowadays, treatment of inflammatory auto- immune diseases, such as rheumatoid arthritis, is di- rected toward inhibition of inflammation and tissue destruction by the use of immunosuppressive agents, such as glucocorticoids and nonsteroidal antiinflamma- tory drugs, as well as disease-modifying drugs (1). The aim of the present study was to investigate possible new therapeutic strategies based on the hypothesis that the intestinal bacterial flora is important in the regulation of inflammatory autoimmune diseases. Experiments have previously been performed to investigate whether the presence of bacteria in the gut modulates the symptoms of adjuvant-induced arthritis (AIA). Rats raised under germ-free conditions were found to be more susceptible to AIA than were normally colonized animals (2,3). Interestingly, introduction of Escherichia coli, but not Lactobacillus species, in the intestine of germ-free rats decreased disease severity (2–4). More recently, antibiotic treatment has been applied in a rat arthritis model to eradicate putative arthritogenic bacteria. However, decontamination of both gram-positive and gram-negative bacteria was inef- fective in preventing arthritis in these rats (5). The present study was designed to create a shift in the endogenous intestinal flora and examine its effects on AIA. We aimed at increasing the intestinal concen- tration of E coli, as well as the level of luminal lipopoly- saccharide (LPS) by treating rats orally with vancomycin (6) after induction of AIA. Vancomycin is bactericidal to most gram-positive bacteria, whereas all gram-negative bacteria are vancomycin-resistant (7). Vancomycin is not absorbed by the intestine (7) and therefore cannot exert direct effects on inflammatory cells at the site of inflam- mation. Specifically, we investigated the effect of changes in intestinal flora on the course of AIA. AIA is an animal model of rheumatoid arthritis that is induced by immunization of Lewis rats with Mycobacterium tubercu- Supported by STER grant SW07 from the UMC Utrecht. Edward E. S. Nieuwenhuis, MD, Annemieke Kavelaars, PhD, Pieter M. Cobelens, PhD, Cobi J. Heijnen, PhD: Wilhelmina Chil- dren’s Hospital, Utrecht, The Netherlands; Maarten R. Visser, MD, PhD, Andre Fleer, MD, PhD, Wil Harmsen, Jan Verhoef, MD, PhD, Louis M. A. Akkermans, PhD: University Medical Center Utrecht, Utrecht, The Netherlands. Address reprint requests to Cobi J. Heijnen, PhD, Depart- ment of Pediatric Immunology, Room KC 03.068.0, Wilhelmina Children’s Hospital of the University Medical Center Utrecht, Lund- laan 6, 3584 EA Utrecht, The Netherlands. Submitted for publication March 10, 2000; accepted in revised form June 25, 2000. 2583