Bone marrow is thought to be a primary hematopoietic organ. However, accumulated evidences demonstrate that active function and trafficking of immune cells including regulatory T cells, conventional T cells, B cells, dendritic cells, NKT cells, Neutrophils, myeloid-derived suppressor cells and mesenchymal stem cells are observed in the bone marrow. Furthermore, bone marrow is a predetermined metastatic location for multiple human tumors. In this review, we discuss the immune network in the bone marrow. We suggest that bone marrow is an immune regulatory organ capable of fine tuning immunity and may be a potential therapeutic target for immunotherapy and immune vaccination.
Multiple modes of suppressive mechanisms including IL-10 are thought to be implicated in CD4+CD25+ regulatory T (Treg) cell-mediated suppression. However, the cellular source, role, and molecular mechanism of IL-10 in Treg cell biology remain controversial. We now studied the interaction between Treg cells and APCs. We demonstrate that Treg cells, but not conventional T cells, trigger high levels of IL-10 production by APCs, stimulate APC B7-H4 expression, and render APCs immunosuppressive. Initial blockade of B7-H4 reduces the suppressive activity mediated by Treg cell-conditioned APCs. Further, APC-derived, rather than Treg cell-derived, IL-10 is responsible for APC B7-H4 induction. Therefore, Treg cells convey suppressive activity to APCs by stimulating B7-H4 expression through IL-10. Altogether, our data provide a novel cellular and molecular mechanism for Treg cell-mediated immunosuppression at the level of APCs, and suggest a plausible mechanism for the suppressive effect of IL-10 in Treg cell-mediated suppression.
Summary The difficulty in detecting rare infected cells immediately after mucosal HIV transmission has hindered our understanding of the initial cells targeted by the virus. Working with the macaque-simian immunodeficiency virus (SIV) vaginal challenge model, we developed methodology to identify discrete foci of SIV (mac239) infection 48 hours after vaginal inoculation. We find infectious foci throughout the reproductive tract, from labia to ovary. Phenotyping infected cells reveals that SIV has a significant bias for infection of CCR6+ CD4+ T cells. SIV infected cells expressed the transcriptional regulator RORγt confirming that the initial target cells are specifically of the Th17 lineage. Furthermore, we detect host responses to infection, as evidenced by apoptosis, cell lysis, and phagocytosis of infected cells. Thus, our analysis identifies Th17 lineage CCR6+ CD4+ T cells as primary targets of SIV during vaginal transmission. This opens new opportunities for interventions to protect these cells and prevent HIV transmission.
SUMMARY Innate lymphoid cells (ILCs) are an emerging subset of lymphocytes involved in surveillance against virally infected cells. Here we show CD3−CD8high lymphocytes in macaque blood include major subsets of ILCs including NK cells expressing CD16, NKp46 and NKG2A, but also populations of ILCs in mucosal tissues having different properties. One ILC subset secreted IL-17 (ILC17), but these were restricted to mucosal tissues. Some mucosal ILC17 cells expressed classical NK-cell markers, but little NKG2A or NKG2D. Some ILC17 cells secreted IL-22 and TNF-α, but few produced IFN-γ or contained granzyme B. IL-17 production by ILCs was induced by IL-6, TGF-β and IL-23. Further, SIV infection resulted in a significant loss of ILC17 cells, especially in the jejunum, which persisted throughout SIV infection. These findings ILC17 cells may be involved in innate mucosal immune responses, and their loss may contribute to loss of intestinal mucosal integrity and disease progression in HIV/SIV infection.
Intestinal CD4+ T cells are rapidly and profoundly depleted in HIV-infected patients and SIV-infected macaques. However, monitoring intestinal cells in humans is difficult, and identifying surrogate markers in the blood, which correlate with loss or restoration of intestinal CD4+ T cells could be helpful in monitoring the success of therapeutic strategies and vaccine candidates. Recent studies indicate HIV utilizes the intestinal homing molecule α4β7 for attachment and signaling of CD4+ T cells, suggesting this molecule may play a central role in HIV pathogenesis. Here we compared β7HIGH integrin expression on CD4+ T cells in blood with loss of CD4+ T cells in the intestine of macaques throughout SIV infection. The loss of β7HIGH CD4+ T cells in blood closely paralleled the loss of intestinal CD4+ T cells, and proved to be a more reliable marker of intestinal CD4+ T cell loss than monitoring CCR5+ memory CD4+ T cells. These data are consistent with a recent hypothesis that α4β7 plays a role in the selective depletion of intestinal CD4+ T cells, and indicate that monitoring β7HIGH expression on CD4+ T cells in the blood may be a useful surrogate for estimating intestinal CD4+ T cell loss and restoration in HIV-infected patients.
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