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Background: Intraventricular hemorrhage (IVH) and associated hydrocephalus are significant complications of intracerebral and subarachnoid hemorrhage. Despite proximity to IVH, the immune cell response at the choroid plexus (ChP) has been relatively understudied. This study employs CX3CR-1GFP mice, which marks multiple immune cell populations, and immunohistochemistry to outline that response. Methods: This study had four parts all examining male adult CX3CR-1GFP mice. Part 1 examined naïve mice. In part 2, mice received an injection 30 µl of autologous blood into right ventricle and were euthanized at 24 h. In part 3, mice underwent intraventricular injection of saline, iron or peroxiredoxin 2 (Prx-2) and were euthanized at 24 h. In part 4, mice received intraventricular iron injection and were treated with either control or clodronate liposomes and were euthanized at 24 h. All mice underwent magnetic resonance imaging to quantify ventricular volume. The ChP immune cell response was examined by combining analysis of GFP(+) immune cells and immunofluorescence staining. Results: IVH and intraventricular iron or Prx-2 injection in CX3CR-1GFP mice all induced ventriculomegaly and activation of ChP immune cells. There were very marked increases in the numbers of ChP epiplexus macrophages, T lymphocytes and neutrophils. Co-injection of clodronate liposomes with iron reduced the ventriculomegaly which was associated with fewer epiplexus and stromal macrophages but not reduced T lymphocytes and neutrophils. Conclusion: There is a marked immune cell response at the ChP in IVH involving epiplexus cells, T lymphocytes and neutrophils. The blood components iron and Prx-2 may play a role in eliciting that response. Reduction of ChP macrophages with clodronate liposomes reduced iron-induced ventriculomegaly suggesting that ChP macrophages may be a promising therapeutic target for managing IVH-induced hydrocephalus. [ABSTRACT FROM AUTHOR]