Increased monocyte turnover from bone marrow correlates with severity of SIV encephalitis and CD163 levels in plasma.

Cells of the myeloid lineage are significant targets for human immunodeficiency virus (HIV) in humans and simian immunodeficiency virus (SIV) in monkeys. Monocytes play critical roles in innate and adaptive immunity during inflammation. We hypothesize that specific subsets of monocytes expand with AIDS and drive central nervous system (CNS) disease. Additionally, there may be expansion of cells from the bone marrow through blood with subsequent macrophage accumulation in tissues driving pathogenesis. To identify monocytes that recently emigrated from bone marrow, we used 5-bromo-2'-deoxyuridine (BrdU) labeling in a longitudinal study of SIV-infected CD8+ T lymphocyte depleted macaques. Monocyte expansion and kinetics in blood was assessed and newly migrated monocyte/macrophages were identified within the CNS. Five animals developed rapid AIDS with differing severity of SIVE. The percentages of BrdU+ monocytes in these animals increased dramatically, early after infection, peaking at necropsy where the percentage of BrdU+ monocytes correlated with the severity of SIVE. Early analysis revealed changes in the percentages of BrdU+ monocytes between slow and rapid progressors as early as 8 days and consistently by 27 days post infection. Soluble CD163 (sCD163) in plasma correlated with the percentage of BrdU+ monocytes in blood, demonstrating a relationship between monocyte activation and expansion with disease. BrdU+ monocytes/macrophages were found within perivascular spaces and SIVE lesions. The majority (80-90%) of the BrdU+ cells were Mac387+ that were not productively infected. There was a minor population of CD68+BrdU+ cells (<10%), very few of which were infected (<1% of total BrdU+ cells). Our results suggest that an increased rate of monocyte recruitment from bone marrow into the blood correlates with rapid progression to AIDS, and the magnitude of BrdU+ monocytes correlates with the severity of SIVE.

Combined Id1 and Id3 Deletion Leads to Severe Erythropoietic Disturbances.

The Inhibitor of DNA Binding (Id) proteins play a crucial role in regulating hematopoiesis and are known to interact with E proteins and the bHLH family of transcription factors. Current efforts seek to elucidate the individual roles of Id members in regulating hematopoietic development and specification. However, the nature of their functional redundancies remains elusive since ablation of multiple Id genes is embryonically lethal. We developed a model to test this compensation in the adult. We report that global Id3 ablation with Tie2Cre-mediated conditional ablation of Id1 in both hematopoietic and endothelial cells (Id cDKO) extends viability to 1 year but leads to multi-lineage hematopoietic defects including the emergence of anemia associated with defective erythroid development, a novel phenotype unreported in prior single Id knockout studies. We observe decreased cell counts in the bone marrow and splenomegaly to dimensions beyond what is seen in single Id knockout models. Transcriptional dysregulation of hematopoietic regulators observed in bone marrow cells is also magnified in the spleen. E47 protein levels were elevated in Id cDKO bone marrow cell isolates, but decreased in the erythroid lineage. Chromatin immunoprecipitation (ChIP) studies reveal increased occupancy of E47 and GATA1 at the promoter regions of ß-globin and E2A. Bone marrow transplantation studies highlight the importance of intrinsic Id signals in maintaining hematopoietic homeostasis while revealing a strong extrinsic influence in the development of anemia. Together, these findings demonstrate that loss of Id compensation leads to dysregulation of the hematopoietic transcriptional network and multiple defects in erythropoietic development in adult mice.