Effect of Intestinal Microflora on the Production of Interleukin 10 and Prostaglandin E2 in Serum and Kupffer Cells from Germfree and Conventional Mice

To determine why germfree (GF) mice are less productivity of proinflammatory cytokines than conventional (CV) mice, we studied serum levels of interleukin 10 (IL-10) and prostaglandin E2 (PGE2) in mice after treatment with lipopolyssacharide (LPS). A single injection of LPS caused an elevation of IL-10 in serum from GF, LPS-GF (germfree mice given drinking water containing LPS) and CV mice. The response was highest in serum from GF mice, and was lower in serum from LPS-GF mice compared with GF mice. Before LPS injection, serum PGE2 was significantly higher in CV and LPS-GF mice than in GF ones. After LPS injection, a higher level of PGE2 was maintained over 12 h in CV mice after LPS injection, while the LPS treatment reduced the level in LPS-GF mice and increased the level in GF mice. The levels of IL-10 in culture medium from Kupffer cells treated with LPS showed similar results to serum in GF and CV mice. These results suggest that high levels of IL-10 in serum from germfree mice may be partly responsible for the lower in vivo responsiveness of these proinflammatory cytokines to LPS in these mice, although PGE2 was not responsible for the lower responsiveness of these inflammatory cytokines to LPS.