Symbols represent normalized 2−ΔΔCt values (n=8 biological replicates/sex/surgical condition) compared to the average of four reference genes. All male vs. female t-test values p>0.40, except for P2rx4: t 14 = 3.5, p=0.003. **p<0.01 compared to other sex. In male mice, P2X 4 R gene expression is under the transcriptional control of interferon regulatory factors 5 and 8 (IRF5 and IRF8). Following peripheral nerve injury, IRF8 is upregulated and directs gene expression changes associated with microglial reactivity, including motility, chemotaxis, Iba1 expression and increases in IRF5 (Masuda et al., Nat. Commun. 2014; Masuda et al., Purinergic Signal., 2014). IRF5 binds directly to the promoter region of P2rx4 and has direct transcriptional control over it, resulting in de novo expression of microglial P2X 4 R after peripheral nerve injury. Following nerve injury, Irf8 is upregulated (and, as shown above, equally in males and females), with a consequent spinal microglial proliferation and upregulation of Itgam (and Aif1, which codes for Iba1). Irf5 is in turn upregulated and, in males but not females, leads to increased P2rx4 gene expression. However, in females, despite the increased IRF5, P2rx4 expression is unaffected. This pattern of gene expression changes after nerve injury shows the point of divergence in the cellular and molecular pathways underlying neuropathic pain in male and female mice lies at the induction of P2X 4 R.