Primed Activation of Macrophages by Oral Administration of Lipopolysaccharide Derived from Pantoea agglomerans

Abstract

Background/aim: Bacterial lipopolysaccharide (LPS) is involved in the activation of the innate immune responses on monocytes/macrophages in vitro, and by intravenous injection. Although small quantities of LPS are usually found in traditional Chinese medicines, vegetables and fruits, the mode of action of orally administered LPS is still unclear.

Materials and methods: LPS derived from Pantoea agglomerans (LPSp) was orally administered to C3H/HeN or C3H/HeJ mice ad libitum.

Results: The LPSp treatment enhanced phagocytosis by resident peritoneal macrophages of C3H/HeN mice but not of C3H/HeJ mice. This activation can be defined as primed activation because no augmentation of inflammatory cytokines production was detected. LPSp in peritoneal fluid was detected and successfully quantified. Moreover, the LPSp reduced the expression of avian reticuloendotheliosis viral oncogene-related B (RelB) in the macrophages without degradation of nuclear factor of kappa light polypeptide gene enhancer in B-cell inhibitor, alpha (IκBα).

Conclusion: Orally administered LPSp can reach the peritoneum, and enhance phagocytosis via Toll-like receptor 4 signaling pathway in resident peritoneal macrophages.

Keywords: LPS; Pantoea agglomerans; macrophage; oral administration; priming.