Fig. 4

Monocyte-derived macrophages join resident microglia in the resident immune mosaic following acute photoreceptor degeneration. A Maximum intensity projections through the inner plexiform layers of WT and Arr1^−/− (KO) retinas after 20 days of light exposure utilizing an inducible fluorescent lineage tracing paradigm (Arr1^{+/+ or −/−} Ai9^KI/KI Cx3cr1^{+/YFP−CreER} post-tamoxifen). Resident macrophages express both YFP and tdTomato, whereas monocyte-derived macrophages express only YFP. In the pseudocolored images, YFP⁺tdTomato⁺ (resident) cells have been pseudocolored peach, and YFP⁺tdTomato⁻ (monocytic) cells have been pseudocolored blue. Scale bar indicates 50 μm. B Gating for flow cytometry to quantify resident and peripherally derived macrophages. An intravenous CD45 antibody (CD45-IV) was used to exclude immune cells in the vasculature that may have been captured during tissue dissection. C Quantification of resident (YFP⁺tdTomato⁺) and peripherally derived (YFP⁺tdTomato⁻) macrophages using flow cytometry before (0 days), immediately after (7 days), and well after (20 days) photoreceptor loss (mean ± SE). **p < 0.01, ***p < 0.001; n = 6 retinas (3 mice) per time point