Irene Nepomnaschy

Mouse bone marrow-derived mesenchymal stromal cells turn activated macrophages into a regulatory-like profile.

In recent years it has become clear that the therapeutic properties of bone marrow-derived mesenchymal stromal cells (MSC) are related not only to their ability to differentiate into different lineages but also to their capacity to suppress the immune response. We here studied the influence of MSC on macrophage function. Using mouse thioglycolate-elicited peritoneal macrophages (M) stimulated with LPS, we found that MSC markedly suppressed the production of the inflammatory cytokines TNF-α, IL-6, IL-12p70 and interferon-γ while increased the production of IL-10 and IL-12p40. Similar results were observed using supernatants from MSC suggesting that factor(s) constitutively released by MSC are involved. Supporting a role for PGE2 we observed that acetylsalicylic acid impaired the ability of MSC to inhibit the production of inflammatory cytokines and to stimulate the production of IL-10 by LPS-stimulated M. Moreover, we found that MSC constitutively produce PGE2 at levels able to inhibit the production of TNF-α and IL-6 by activated M. MSC also inhibited the up-regulation of CD86 and MHC class II in LPS-stimulated M impairing their ability to activate antigen-specific T CD4+ cells. On the other hand, they stimulated the uptake of apoptotic thymocytes by M. Of note, MSC turned M into cells highly susceptible to infection with the parasite Trypanosoma cruzi increasing more than 5-fold the rate of M infection. Using a model of inflammation triggered by s.c. implantation of glass cylinders, we found that MSC stimulated the recruitment of macrophages which showed a low expression of CD86 and the MHC class II molecule Iab and a high ability to produce IL-10 and IL-12p40, but not IL-12 p70. In summary, our results suggest that MSC switch M into a regulatory profile characterized by a low ability to produce inflammatory cytokines, a high ability to phagocyte apoptotic cells, and a marked increase in their susceptibility to infection by intracellular pathogens.

Toll-Like Receptor 4-Dependent Activation of Dendritic Cells by a Retrovirus

ABSTRACT Mouse mammary tumor virus (MMTV) is a milk-borne retrovirus that exploits the adaptive immune system. It has recently been shown that MMTV activates B cells via Toll-like receptor 4 (TLR4), a molecule involved in innate immune responses. Here, we show that direct virus binding to TLR4 induced maturation of bone marrow-derived dendritic cells and up-regulated expression of the MMTV entry receptor (CD71) on these cells. In vivo, MMTV increased the number of dendritic cells in neonatal Peyers patches and their expression of CD71; both these effects were dependent on TLR4. Thus, retroviral signaling through TLRs plays a critical role in dendritic-cell participation during infection.

Differential susceptibility to acute Trypanosoma cruzi infection in BALB/c and C57BL/6 mice is not associated with a distinct parasite load but cytokine abnormalities

Inoculation of Trypanosoma cruzi, Tulahuén strain, into C57BL/6 and BALB/c mice led to an acute infection characterized by marked parasitaemia, myocardial inflammation and thymocyte depletion. While C57BL/6 mice showed a progressive and lethal disease, BALB/c mice partly recovered. To characterize these murine models more effectively, we studied the parasite burden, serum levels of major infection outcome‐related cytokines, the in vitro features of T. cruzi infection in peritoneal macrophages and the immunophenotype of thymic cells. The greater disease severity of T. cruzi‐infected C57BL/6 mice was not linked to an increased parasite load, as parasitaemia, myocardial parasite nests and amastigote counts in peritoneal macrophages were not different from those in BALB/c mice. Cortical thymocyte loss was accompanied by the presence of apoptotic bodies and fragmented nuclear DNA, whereas fluorocytometric analysis at 17 days postinfection (p.i.) revealed a more pronounced loss of CD4+ CD8+ cells in C57BL/6 mice. This group displayed higher levels of TNF‐α on days 14 and 21 p.i., in the presence of lower IL‐1β and IL‐10 concentrations by days 14 and 21, and days 7 and 14 p.i., respectively. Day‐21 evaluation showed higher concentrations of nitrate and TNF‐α soluble receptors in C57BL/6 mice with no differences in IFN‐γ levels, with respect to the BALB/c group. Increased morbidity of C57BL/6 T. cruzi‐infected mice does not seem to result from an aggravated infection but from an unbalanced relationship between pro‐ and anti‐inflammatory mediators.

Cathepsin-L Influences the Expression of Extracellular Matrix in Lymphoid Organs and Plays a Role in the Regulation of Thymic Output and of Peripheral T Cell Number

Nackt mice, which are deficient in cathepsin-L (CTSL), show an early impairment during positive selection in the context of class II MHC molecules and as a consequence, the percentage and absolute number of CD4+ thymocytes are significantly decreased. In this study, we show that lymph nodes from nackt mice are hypertrophied, showing normal absolute numbers of CD4+ T cells and marked increases in the number of CD8+ T lymphocytes. Basal proliferative levels are increased in the CD4+ but not in the CD8+ population. Lymph node T cells show increases in the expression of α5, α6, and β1 integrin chains. These alterations correlate with increases in the expression of extracellular matrix (ECM) components in lymph nodes. Interestingly, laminin, fibronectin, and collagen I and IV are markedly decreased in nackt thymus which shows an augmented output of CD8+ cells. These results demonstrate that a mutation in the Ctsl gene influences the levels of ECM components in lymphoid organs, the thymic output, and the number of T cells in the periphery. They further raise the possibility that, by regulating the level of expression of ECM components in lymphoid organs, CTSL is able to broadly affect the immune system.

Critical Role of Dendritic Cells in Mouse Mammary Tumor Virus In Vivo Infection

ABSTRACT Mouse mammary tumor virus (MMTV) is a milk-transmitted betaretrovirus that causes mammary tumors in mice. Although mammary epithelial cells are the ultimate targets of MMTV, the virus utilizes components of the host immune system to establish infection. Previous studies indicated that dendritic cells play a role in MMTV infection. Here we show that dendritic cells are the first cells to be infected by MMTV in vivo and that they are capable of producing infectious virus that can be transmitted to other cell types. Moreover, upon contact with the virus, dendritic cells became more mature and migrated in response to the chemokine macrophage inflammatory protein 3β. Finally, we demonstrate that targeted ablation of dendritic cells in vivo dramatically attenuated MMTV infection. These data indicate that MMTV infection of dendritic cells is critical to initial propagation of the virus in vivo.

Regulation of parental alloreactivity by reciprocal F1 hybrids. The role of lactation

Adult reciprocal F1 hybrids differ in their susceptibility to parental graft versus host (GvH) reactions. These reactions were lower when the donor strain was syngeneic with the maternal one. Splenocytes from the member of the reciprocal pair in which the GvH reactions were lower also induced a decreased response of parental cells in cytotoxicity assays and in mixed lymphocyte reactions (MLR). The treatment with anti-CD8 plus complement was able to abrogate the different stimulatory ability of the reciprocal F1 spleen populations. Foster-nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their splenocytes to induce both parental anti-F1 MLR and CTL. The stimulatory ability was indistinguishable from that observed in the reciprocal F1 combination nursed on its own mother. Moreover, lactation was able to alter the ability of CD8+ spleen cells to regulate CTL and parental anti-F1 MLR. The results reported herein show the existence of a maternal effect acting though milk capable of altering the regulation of parental alloreactive T reactions towards self histocompatibility antigens.

Early increase in graft-versus-host reactivity during pregnancy in the mouse

Alloreactive T levels of para-aortic lymph nodes (PALN) and spleen were determined on different days of pregnancy in BALB/c females by local and systemic graft-versus-host (GvH) assays. A significant increase in GvH reactivity was registered early in both allogeneic and syngeneic matings, operating not only towards paternal but also towards third party strains. Immunoregulatory mechanisms in PALN also involved the appearance of progressive suppression during the first days of pregnancy. The possible role of non-specific early increases in T alloreactivity in triggering suppressor mechanisms and the nature of the immunogens responsible for the alterations in GvH reactivity are discussed.

Early Increases in Superantigen-Specific Foxp3+ Regulatory T Cells during Mouse Mammary Tumor Virus Infection

ABSTRACT Mouse mammary tumor virus (MMTV) is a milk-borne betaretrovirus that has developed strategies to exploit and subvert the host immune system. Here, we show in a natural model of MMTV infection that the virus causes early and progressive increases in superantigen (SAg)-specific Foxp3+ regulatory T cells (Treg) in Peyers patches (PP). These increases were shown to be dependent on the presence of dendritic cells. CD4+ CD25+ T cells from the PP of infected mice preferentially suppress the proliferative response of T cells to SAg-expressing antigen-presenting cells ex vivo. We investigated the influence of the depletion of CD25+ cells at different stages of the infection. When CD25+ cells were depleted before MMTV infection, an increase in the number of PP SAg-cognate Foxp3− T cells was found at day 6 of infection. Since the SAg response is associated with viral amplification, the possibility exists that Treg cells attenuate the increase in viral load at the beginning of the infection. In contrast, depletion of CD25+ cells once the initial SAg response has developed caused a lower viral load, suggesting that at later stages Treg cells may favor viral persistence. Thus, our results indicated that Treg cells play an important and complex role during MMTV infection.

Neonatal infection with a milk-borne virus is independent of β7 integrin- and L-selectin-expressing lymphocytes

Mouse mammary tumor virus (MMTV) is acquired by neonates through milk and first infects lymphocytes in Peyers patches. We show here that newborn mice lacking β7 integrin or L‐selectin were infected with MMTV at wild‐type levels in both their lymphoid and mammary tissues. Superantigen‐mediated activation and cognate T cell deletion were also unimpaired in both types of null mice. A large proportion of neonatal Peyers patch lymphocytes in wild‐type mice were β7 and β1 integrin low and both populations increased in response to MMTV infection. These results suggest that adhesion molecules other than β7 integrin or L‐selectin play a role in lymphocyte homing in the gut, peripheral lymph nodes and mammary gland in response to MMTV infection.

Maternal influence on the immune response: SMLC reactions between identical and reciprocal F1 hybrids and the role of lactation

Identical and reciprocal adult F1 mice from different strain combinations, either nursed on their own mothers or foster-nursed on mothers from the paternal strain, were used to carry out SMLC assays. The results obtained showed that: (1) in vitro proliferation of F1 T cells was significantly different when splenocytes from identical versus reciprocal hybrids were used as the stimulatory population, splenocytes from one of the members of the reciprocal pair being able to induce higher proliferative responses of T cells from both identical and reciprocal F1 hybrids; (2) foster-nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their splenocytes to stimulate the proliferation of responder F1 T cells. The stimulatory ability of splenocytes from foster-nursed hybrids was indistinguishable from that observed in the reciprocal F1 combination nursed by its own mother. The existence of a maternal effect acting through milk on the outcome of self recognition in the litter is discussed.