Figure 1.

Summary of potential interactions between macrophages and cell death. Macrophages express a variety of machinery for detecting cell death and products released from cells or the surrounding matrix as a result of necrotic death. These include receptors for complement opsonized cells (CR1, CR3, CR4, CRIg, C1qR); complement cascade components (C3aR, C5aR); DNA/RNA (endosomal TLRs 3, 7, & 9); purines (P2X₇, P2Y₂); monosodium urate (CD14/TLRs); S100 proteins (RAGE); HMGB1 (RAGE, TLRs); heat shock proteins (TLRs, SR-A1); the matrix components fibrin, hyaluronic acid, and heparin sulfate (TLRs); and cytokine alarmins such as IL-1β and IL-33 (IL-1R, ST2). This list is not exhaustive and additional interactions are continuously being described and investigated. It is still unclear to what extent these interactions are involved in AKI and if macrophage stimulation is a critical element for bridging injury and pathogenic inflammation, but it is clear there are multiple avenues for macrophages to engage with cell death events in a tissue setting.