Low TLR4 Expression by Liver Dendritic Cells Correlates with Reduced Capacity to Activate Allogeneic T Cells in Response to Endotoxin

Abstract

Signaling via TLRs results in dendritic cell (DC) activation/maturation and plays a critical role in the outcome of primary immune responses. So far, no data exist concerning TLR expression by liver DC, generally regarded as less immunostimulatory than secondary lymphoid tissue DC. Because the liver lies directly downstream from the gut, it is constantly exposed to bacterial LPS, a TLR4 ligand. We examined TLR4 expression by freshly isolated, flow-sorted C57BL/10 mouse liver DC compared with spleen DC. Real-time PCR revealed that liver CD11c+CD8α− (myeloid) and CD11c+CD8α+ (“lymphoid-related”) DC expressed lower TLR4 mRNA compared with their splenic counterparts. Lower TLR4 expression correlated with reduced capacity of LPS (10 ng/ml) but not anti-CD40-stimulated liver DC to induce naive allogeneic (C3H/HeJ) T cell proliferation. By contrast to LPS-stimulated splenic DC, these LPS-activated hepatic DC induced alloantigen-specific T cell hyporesponsiveness in vitro, correlated with deficient Th1 (IFN-γ) and Th2 (IL-4) responses. When higher LPS concentrations (≥100 ng/ml) were tested, the capacity of liver DC to induce proliferation of T cells and Th1-type responses was enhanced, but remained inferior to that of splenic DC. Hepatic DC activated by LPS in vivo were inferior allogeneic T cell stimulators compared with splenic DC, whereas adoptive transfer of LPS-stimulated (10 ng/ml) liver DC induced skewing toward Th2 responses. These data suggest that comparatively low expression of TLR4 by liver DC may limit their response to specific ligands, resulting in reduced or altered activation of hepatic adaptive immune responses.

PD‐L1 expression on tolerogenic APCs is controlled by STAT‐3

“…For example, the liver has to deal with gutderived portal blood that contains high concentrations of bacterial products. It has been demonstrated that liver DCs have reduced T-cell stimulatory capacities [47,48]. The data of Lunz et al [49] support these findings.…”

Organ-derived dendritic cells have differential effects on alloreactive T cells

“…These results may have been biased due to a lack of sensitivity of hepatic dendritic cells to LPS. 47 However, this was shown for a much lower concentration than used here, and in some cases we additionally substituted LPS with recombinant CD40L, obtaining the same results (data not shown). Foxp3 ϩ CD4 ϩ T cells were not increased ( Figure 3F).…”

Functional modification of CD11c+ liver dendritic cells during liver regeneration after partial hepatectomy in mice†

“…Real-time polymerase chain reaction (RT-PCR) was performed on an ABI Prism 7900 PCR cycler (Applied Biosystems, Foster City, CA) as described. 28 The following validated PCR primers and TaqMan MGB probes (FAM labeled) were used: murine IL-10 (Assay ID: 4329593T), interferon gamma (IFN-␥) (Assay ID: 4339850T), ER-␣ (Assay ID: 4331182 Hs 00174860) and 18S ribosomal RNA (Assay ID: 4333760F) as endogenous control. PCR mix was prepared according to the manufacturer's instructions (Assay on Demand; Applied Biosystems), and thermal cycler conditions were as follows: 1 ϫ 2 min 50°C, 1 ϫ 10 min 95°C, 40 to 50 cycles denaturation (15 s, 95°C) and combined annealing/extension (1 minute, 60°C).…”