P021 The influence of short-chain fatty acids produced by commensal bacteria on macrophage phenotype
C. Jukes1,2, L. Ricci3, E. von Coburg1,2, M. Nasr4, A.W. Walker3, S.H. Duncan3, A.N. Hegazy MD, PhD1,2
1Charité, University Medicine Berlin, CBF and German Rheumatism Research Center-Berlin, Department of Gastroenterology, Infectiology and Rheumatology, Berlin, Germany, 2Deutsches Rheuma-Forschungszentrum- ein Institut der Leibniz-Gemeinschaft, Inflammatory Mechanisms Group, Berlin, Germany, 3Rowett Institute, University of Aberdeen, Gut Health Group, Aberdeen, UK, 4Department of Pharmaceutics and Industrial Pharmacy, Ain Shams University, Faculty of Pharmacy, Cairo, Egypt
Background
Macrophages are dynamic immune cells that react to environmental signals to adapt to their environment. Among this diverse array of signals are multiple bacterially derived metabolites including short-chain fatty acids (SCFAs) in the gastrointestinal tract. It has been previously shown that butyrate, one of several SCFAs produced by bacteria, is able to drive an antimicrobial phenotype in macrophages. However, it is still unknown which bacterial species are able to drive this impact and whether this effect can be recapitulated
Methods
Monocytes were differentiated into macrophages in the presence of SFCAs or bacterial supernatants from a wide range of gut commensals isolated from healthy human donors. RNA was isolated post-differentiation and gene expression screened using a defined gene panel using the Fluidgm Biomark system. In addition, cytokines present in the supernatant were measured by ELISA and the ability of the macrophages to kill intracellular bacteria determined. Currently, we are carrying out the same procedure using bone marrow-derived macrophages (BMDM) from mice in order to expand this work flow into the mouse system so that we can determine if bacteria identified can elicit their impact
Results
We have screened numerous SCFAs alone and in combination in the bacterial killing assay to determine how these are able to influence macrophage phenotype. From these experiments, we have repeated the earlier observation that butyrate can increase macrophage killing of intracellular bacteria. In addition, we have identified four bacterial isolates that induce significantly increased microbial killing in macrophages. This is associated with the production of butyrate, acetate and formate. Using RNA from these different conditions, we are in the process of determining if there is a common molecular pathway by which this increased antimicrobial phenotype is driven.
Conclusion
Both SCFAs and SCFA producing bacteria are able to induce an antimicrobial phenotype in macrophages that increased the ability of these cells to kill intracellular pathogens. Identification of a common signature that drives these changes could help to screen bacterial isolates for this beneficial trait. Ongoing work hopes to identify such a signature, to enable us to screen large numbers of commensals using high-throughput molecular methods. This can then be verified using both