Abstract 091: High Salt Promotes Conversion of Human Monocytes Into Dendritic Cells via Formation of Immunogenic Isoketals

Abstract

High salt intake and inflammation are implicated in the genesis of hypertension. Recently it has become clear that sodium can accumulate in the interstitial space in concentrations exceeding that of the plasma, and that these high salt (HS) concentrations can be pro-inflammatory. Our laboratory recently published a new pathway in which increased oxidative stress in dendritic cells (DCs) leads to formation of isoketal-modified proteins which act as neo-antigens to activate T cells. We hypothesized that increasing sodium chloride (NaCl) in excess activates antigen presenting cells via formation of immunogenic isoketals. We exposed monocytes from human volunteers to normal physiological NaCl (NS: 150 mM/L), elevated NaCl concentrations (HS: 190 mM/L), or an equiosmoloar concentration of mannitol. We found that exposure of human monocytes to high salt, but not mannitol, caused a 2-fold increase in formation of isoketal-modified proteins. This was associated with an increase in activation marker CD86 (NS: 466 ± 192 vs HS: 596 ± 324 MFI p<0.05) and production of inflammatory cytokines IL-6, IL-β and TNF-α. Interestingly, these cells expressed surface markers indicative of transformation to DCs, as evidenced by their acquisition of surface marker CD83. In additional immunofluorescence studies, we found that monocytes exposed to HS for 7 days acquire a DC like morphology. Moreover, using flow cytometry, we confirmed that high salt exposure causes these cells to lose the monocyte marker CD14 (NS: 41.1 ± 15.4 vs HS: 19.9 ± 6.4 MFI; p<0.05), and gain the DC marker CD209 (NS: 24.2 ± 1.0 vs HS: 49.3 ± 0.7 MFI; p<0.001). None to these effects were mimicked by mannitol and scavenging of isoketals during high salt exposure. High salt dramatically increased mRNA expression of GM-CSF (NS: 758 ± 440.8 vs HS: 5476 ± 2268 MFI; p<0.05), IL-4 NS: 1868 ± 560.6 vs HS: 4867 ± 1152 MFI; p<0.05) and Flt3 (NS: 2526 ± 636.8 vs HS: 10014 ± 2370 MFI; p<0.05), which are known to mediate monocyte conversion to DCs. Thus, we have defined a novel pathway whereby high NaCl concentrations lead to transformation of monocytes to DCs due to increased formation of immunogenic isoketals. These observations provide insight into how elevated sodium environments lead to an inflammatory state.