Human Anti-Human IRF-8 monoclonal Antibody, clone SFB627 [PE]

Neonatal hindpaw incision primes developing spinal nociceptive circuitry, resulting in enhanced hyperalgesia following reinjury in adulthood. Spinal microglia contribute to this persistent effect, and microglial inhibition at the time of adult reincision blocks the enhanced hyperalgesia. Here, we pharmacologically inhibited microglial function with systemic minocycline or intrathecal SB203580 at the time of neonatal incision and evaluated sex-dependent differences following adult reincision. Incision in adult male and female rats induced equivalent hyperalgesia and spinal dorsal horn expression of genes associated with microglial proliferation (Emr1) and transformation to a reactive phenotype (Irf8). In control adults with prior neonatal incision, the enhanced degree and duration of incision-induced hyperalgesia and spinal microglial responses to reincision were equivalent in males and females. However, microglial inhibition at the time of the neonatal incision revealed sex-dependent effects: the persistent mechanical and thermal hyperalgesia following reincision in adulthood was prevented in males but unaffected in females. Similarly, reincision induced Emr1 and Irf8 gene expression was downregulated in males, but not in females, following neonatal incision with minocycline. To evaluate the distribution of reincision hyperalgesia, prior neonatal incision was performed at different body sites. Hyperalgesia was maximal when the same paw was reincised, and was increased following prior incision at ipsilateral, but not contralateral, sites, supporting a segmentally restricted spinal mechanism. These data highlight the contribution of spinal microglial mechanisms to persistent effects of early-life injury in males, and sex-dependent differences in the ability of microglial inhibition to prevent the transition to a persistent pain state span developmental stages.

The transcription factor, interferon regulatory factor-8 (IRF8), is required for the development of monocytes, macrophages, dendritic cells (DCs), basophils, and eosinophils, while it inhibits the generation of neutrophils. Recently, the molecular mechanisms by which IRF8 regulates their development have been increasingly clarified by genome-wide analyses, including chromatin immunoprecipitation-sequencing and transcriptome profiling. IRF8 associates with the myeloid master transcription factor, PU.1, to promote the establishment of cell-type-specific enhancers and gene expression, thereby driving monocyte development or maintaining the plasmacytoid DC-specific gene expression profiles. Furthermore, microbial stimulation enables IRF8 to associate with other transcription factors, including IRF1, to induce immune response genes. Knowledge about the regulation of Irf8 expression in myeloid development has also increased. In this review, we discuss recent advances in our understanding of transcriptional and epigenetic regulation involving IRF8 in the development of myeloid cells.