Abstract
BackgroundBacterial infections cause an increase in the population of hematopoietic stem cells (HSCs). To investigate the downstream factors associated with hematopoietic stem cells, mice are infected with Mycobacterium avium (M. avium).Results Mycobacterium avium (M. avium) infection induces the enlargement of the spleen and changes in histopathology, including changes to the lineage populations. A dramatic expansion of Lin−c-kit+Sca-1+ (KSL) cells in mouse bone marrow cells and spleen cells was detected 4 weeks after infection with M. avium; however, there was no difference in the engraft activity between infected and un-infected mouse bone marrow cells. We tested the cytokine and cytokine-related gene expression after M. avium infection and found that IFN-γ expression increased and peaked at 4 weeks in both bone marrow and spleen cells. The expression of Sca-1 gene peaked at 4 weeks in the bone marrow but peaked at 2 weeks in spleen cells, although the Sca-1 surface marker peaked at 4 weeks after infection in both bone marrow and spleen cells. Interferon regulatory factor-2 (IRF-2) expression did not change in the bone marrow cells, whereas it decreased in spleen cells at 4 weeks and IRF-1 expression was up-regulated in both bone marrow and spleen cells after infection. However, the up-regulation of IRF-1 was not correlated with IFN-γ expression in the M. avium-infected mouse spleen cells.ConclusionsThis finding suggests that the IFN-γ production mediated by M. avium infection alters the population of KSL cells during host defense, and the down-regulation of the IFN-γ response in spleen cells occurs at the late stage after M. avium infection.
Highlights
Bacterial infections cause an increase in the population of hematopoietic stem cells (HSCs)
To examine the changes in the bone marrow hematopoietic precursor cell populations following the systemic infection with M. avium, the bone marrow cells were analyzed by flow cytometry on the basis of their hematopoietic surface markers
M. avium treatment, the size of the KSL cell population did not significantly increase in the bone marrow; the KSL population had increased by 2 weeks and reached a maximum size after 4 weeks post-i.v.; this population was decreased at 12 weeks after injection (Fig. 2a)
Summary
Bacterial infections cause an increase in the population of hematopoietic stem cells (HSCs). To investigate the downstream factors associated with hematopoietic stem cells, mice are infected with Mycobacterium avium (M. avium). Hematopoietic stem cells (HSCs) are functionally defined by their unique capacity for self-renewal and differentiation into all types of mature blood cells [1]. Despite the biological significance of changes in hematopoiesis during bacterial infection, relatively, little is known about the downstream factors associated with hematopoietic precursor cells, including hematopoietic stem cells. The bone marrow hematopoietic activity shifts toward granulocyte production, and granulocyte colony-stimulating factor (G-CSF) and chemokines, which are critical for host defenses, are produced [3]. Bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) can be activated by type I IFNs, viruses, and bacterial infection to increase the level of hematopoiesis. The dramatic expansion of the lin-c-kit+Sca-1+ cell pool is induced by bacterial infection due to IFN-γ production [4]
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