Proliferation is a driver of quorum sensing in an in vitro model of tissue resident macrophages

Macrophages coordinate the initial host inflammatory response to tissue infection as well as mediating the reparative phase by producing growth factors that promote tissue repair. One model of this functional dichotomy is that peripherally recruited monocyte-derived macrophages drive acute inflammatory responses to infection, whereas tissue resident macrophages are responsible for tissue repair. Alternatively, inflammation and repair may be inter-dependent molecular programs, such that both recruited and resident cells have equivalent capacity to contribute. In this study, induced pluripotent stem cells or peripheral blood monocytes were used to generate models of tissue-resident and recruited macrophages, respectively. Using single-cell sequencing, we assessed whether lipopolysaccharide activation drives heterogeneous responses in these two macrophage models. We observe heterogeneity at population and gene expression level in the activation programs adopted by either macrophage population. We further identify proliferation to be a driver of quorum sensing in LPS responsiveness. Our findings highlight the usefulness of this model system to explore the differences between recruited and resident macrophages in response to tissue infection. Monocytes(from 3 donors) /progenitor cells (from 3 iPSC lines) were cultured in tissue-culture treated 6 well plates (blood cells from all 3 donors were cultured together. Progenitors from all 3 iPSC lines were cultured together). Cells were cultured in RPMI-1640 medium containing L-Glutamine with 10% Fetal Bovine Serum and 100ng/ml recombinant Human M-CSF for 4 days. On day 4, media was changed and cells left to settle for either 2 hours before stimulation series. Stimulation consisted of either a 2 hour acute stimulation with 10ng/ml LPS, 18 hour stimulation with 10ng/ml LPS, or a 18 hour stimulation, 2 hour rest, and restimulation (tolerance) with 10ng/ml LPS. Cells were collected and processed for 5' single cell sequencing.