Figure 9. An autocrine/paracrine dopamine signaling loop could be an underlying mechanism for DAT modulation of human macrophages.

(A) Schematic description of experimental design. Cultured human macrophages were treated with vehicle (unstimulated), LPS to induce dopamine efflux (increased extracellular dopamine), LPS + nomifensine to block DA efflux (decreased extracellular dopamine), LPS + nomifensine + exogenous dopamine, or LPS + nomifensine + exogenous dopamine + dopamine receptor blockade (Sulpiride and SCH53390). (B) Representative confocal images of PFA fixed cultured human macrophages incubated with fluorescent latex beads to measure phagocytosis under experimental conditions described in A (images for unstimulated condition not shown). (C) Median phagocytic capacity measured as fluorescence intensity of phagocytic beads/cell. (D) Empiric cumulative frequency distribution curves of phagocytic capacity shows that LPS + nomifensine decreases phagocytosis compared with LPS-stimulated macrophages (D-statistic = 0.1529, P = 7 × 10^–8). Increasing extracellular dopamine by adding exogenous dopamine shifted the distribution curve to the right toward the LPS group representing an increase in phagocytosis (D-statistic = 0.1246, P = 2 × 10^–7). Blocking both D1-like and D2-like receptors reversed the effect of extracellular dopamine, shifting the distribution curve back to the left toward the LPS + nomifensine curve, representing a decrease in phagocytosis compared with LPS + nomifensine + dopamine (D-statistic = 0.1844, P = 7 × 10^–16). Images and data from B–D are from n = 596–1153 cells/group from at least 3 experiments/group.