[40] This may reflect model-dependent differences in inflammatory pathophysiology. An alternative explanation is that although cysts are macroscopically small at week 3, other pathophysiological processes (such as cell proliferation) may already be established at this stage, and stimulate macrophage infiltration. The phenotypes of macrophages in PKD may also provide a clue to the role of inflammation. Karihaloo et al. investigated macrophages in two murine models of ADPKD, the Pkd1fl/fl;Pkhd1-Cre and Pkd2WS25/− mouse.[19] In both mouse strains there were increased numbers of F4/80-positive

macrophages compared with disease controls. In Pkd1fl/fl;Pkhd1-Cre mice, Ly6Clow cells comprised the predominant population of macrophages,[19] a phenotype characteristic of alternatively activated macrophages.[12] Clodronate-induced depletion of macrophages EGFR inhibitor in Pkd1fl/fl;Pkhd1-Cre mice resulted in a decrease in circulating monocyte numbers, Ki67-positive cell proliferation, cystic selleck chemical index and blood urea nitrogen (BUN) compared with vehicle-treated controls.[19] These findings suggest that macrophage depletion delays disease progression, which seems inconsistent with the authors’ previous observation of a predominantly Ly6Clow macrophage population which should theoretically

have restorative roles in disease. The proportions of Ly6Clow and Ly6Chigh macrophages were not significantly changed following clodronate treatment, indicating that the improved disease outcomes were not due to selective depletion of one

macrophage subtype.[19] Cyclooxygenase (COX) This implies that in PKD, alternatively activated macrophages may have detrimental rather than restorative roles. Indeed, alternatively activated macrophages can induce cell proliferation.[41] Although cell proliferation facilitates the repair of damaged renal parenchyma in other types of renal injury such as IRI,[41] proliferation, particularly of the CEC, promotes cyst expansion in PKD.[7] Since Karihaloo et al. observed a concomitant decrease in cell proliferation with macrophage depletion,[19] it is plausible that inflammatory cells such as macrophages exacerbate cyst growth in this disease. Although macrophages are the most well-studied infiltrating cell type in PKD, other cells have also been observed (see Table 3). CD45-positive lymphocytes[11] and CD4-positive lymphocytes[10] have been identified in the renal interstitium of ADPKD patients. Lymphocytes were also reported in kidneys of kat2J/kat2J mice,[30] DBA/2FG-pcy mice,[26] and Han:SPRD rats,[36] although lymphocyte-specific markers were not employed in any of these studies. In other inflammatory renal states such as IRI, lymphocytes produce chemokines (e.g. TNF-α and interferon-γ),[71] and may therefore instigate similar inflammatory effects in PKD. McPherson et al. identified interstitial mast cells surrounded by chymase in ADPKD kidney tissue.