"Analysis of single-cell secretion reveals paracrine strategies for coordinating population
responses"
Abstract:
Cell responses are mediated by intermediate signals that are secreted and sensed by the same cells
and are subject to significant cell-to-cell heterogeneity. The propagation of these intermediate
signals by extracellular signaling impacts the collective cell-population response, but the
contribution of autocrine versus paracrine signaling is difficult to analyze. To address this, we have
combined multiplexed, microwell single-cell secretion measurements with cell-population data to
uncover the role of paracrine signaling in shaping the inflammatory response in human
macrophages following toll-like receptor 4 (TLR4) stimulation with lipopolysaccharide (LPS). We
demonstrate that loss of paracrine signaling upon single-cell isolation in microwells significantly
alters secretion of many LPS-stimulated cytokines. Graphical models of these single-cell
“perturbation” data sets specifically uncover dependencies between cytokines in the LPSstimulated network. Interestingly, tumor necrosis factor-α (TNF), the most highly connected
cytokine in the network, exhibits highly heterogeneous secretion, such that a small fraction of cells
appear to drive total TNF output in the cell population. Using a computational model fit to our
single-cell data, we demonstrate that this small fraction of high secretors can amplify the
population response for IL-6 in small cell groups. Overall, our results reveal a novel role for
paracrine cell-to-cell communication in coordinating a rapid and reliable innate immune response
in spite of underlying cell-to-cell heterogeneity.