Hematopoietic and Mesenchymal Stromal Cells: New Immunological Roles During Fungal Infections

Adult stem cells are characterized not only by their regenerative and immunomodulatory capacity but also by their therapeutic potential in various pathologies that include hematological malignancies, cancer, and autoimmune and inflammatory diseases, among others. However, these cells seem to play a paradoxical role during the development of the immune response in some infectious diseases. As an example, Candida albicans can induce the proliferation and differentiation of hematopoietic stem cells (HSCs) and their progenitors, a process known as emergency hematopoiesis. Moreover, Aspergillus fumigatus and C. albicans, once recognized by mesenchymal stromal cells (MSCs), can induce an anti-inflammatory or proinflammatory profile, respectively, and, in turn, these cells can inhibit the growth of these fungal pathogens. Additionally, the transplantation of MSCs, in an experimental pulmonary model of paracoccidioidomycosis, has been shown to exacerbate the inflammatory response. More recently, in vitro studies have shown that MSCs recognize Paracoccidioides brasiliensis through a mechanism mediated by toll-like receptor (TLR)2, TLR4, and Dectin-1, which, in turn, induces a proinflammatory profile. This review describes the main mechanisms and immunomodulatory properties of HSCs and MSCs during infections caused by some medically important fungal pathogens described so far in literature.

Medicinal signaling cells: A potential antimicrobial drug store

Medicinal signaling cells (MSCs) are multipotent cells derived from mammalian bone marrow and periosteum that can be extended in culture. They can keep their ability in vitro to form a variety of mesodermal phenotypes and tissues. Over recent years, there has been great attention over MSCs since they can impact the organ transplantation as well as autoimmune and bacterial diseases. MSCs can secrete different bioactive factors such as growth factors, antimicrobial peptides/proteins and cytokines that can suppress the immune system and prevent infection via direct and indirect mechanisms. Moreover, MSCs are able to increase bacterial clearance in sepsis models by producing antimicrobial peptides such as defensins, cathelicidins, lipocalin and hepcidin. It is the aim of the present review to focus on the antibacterial effector functions of MSCs and their mechanisms of action against the pathogenic microbes.

Murine Macrophage Requires CD11b to Recognize Talaromyces marneffei

Introduction

Talaromyces marneffei (T. marneffei) is an emerging pathogenic fungus. Macrophage-1 antigen (Mac-1, CR3, CD11b/CD18) is an important receptor on innate immune cells and can recognize pathogens. However, the importance of CR3 in phagocytosis of T. marneffei by macrophages and their responses to T. marneffei have not been clarified.

Methods

We show that interaction of mouse peritoneal macrophages (pMacs) or RAW264.7 macrophages with T. marneffei of its conidia spores and yeast cells enhances CR3 expression on macrophages. The phagocytosis rate was determined using flow cytometry, RT-PCR and Western blotting were used to detect CD11b expression, and the levels of IFN-γ, TNF-α, IL-2, IL-4, IL-6 and IL-10 in the co-culture supernatants were determined by ELISA.

Results

Incubation of mouse macrophages with T. marneffei promoted phagocytosis of T. marneffei, which was dramatically mitigated by pretreatment with anti-CD11b antibody or knockdown of CR3 expression on macrophages. Then, interferon γ, tumor necrosis factor α, IL-4, IL-10 and IL-12 production in macrophages incubation with heat-killed T. marneffei was detected. CD11b expression on mouse macrophages was upregulated by T. marneffei. Incubation of T. marneffei promoted phagocytosis of T. marneffei by macrophages and high levels of pro-inflammatory and anti-inflammatory cytokine production by macrophages, which were mitigated and abrogated by pre-treatment with anti-CD11b or knockdown of CD11b expression.

Conclusion

These data indicated that murine macrophage requires CD11b to recognize Talaromyces marneffei and their cytokine responses to heat-killed T. marneffei in vitro.

TGF-α Overexpression in Breast Cancer Bone Metastasis and Primary Lesions and TGF-α Enhancement of Expression of Procancer Metastasis Cytokines in Bone Marrow Mesenchymal Stem Cells

Bone metastasis (BM) is the advanced complication of breast cancer, while bone marrow-derived mesenchymal stem cells (BMSCs) in the microenvironment unclearly contribute to cancer metastasis. This study investigated potential roles of transforming growth factor- (TGF-) α in the interaction between breast cancer and BMSCs in BM. Clinical cases of breast cancer with bone metastasis (BMBC), breast cancer without bone metastasis (Non-BM-BC), and benign fibroadenoma (Benign) were enlisted in a retrospective study. TGF-α was found obviously overexpressed in BM lesion of BMBC compared to primary lesion of both BMBC and Non-BM-BC (P < 0.01), and TGF-α was higher in primary lesion of both BMBC and Non-BM-BC (P < 0.01) than Benign group. Interestingly, TGF-α in nontumor tissues of both BMBC and Non-BM-BC was at a higher level than Benign group (P < 0.01), and numbers of macrophages in nontumor tissues of both BMBC and Non-BM-BC (P < 0.01) were higher than Benign group. Furthermore, in cultured human BMSCs, TGF-α stimulated production of procancer cytokines including IL-6, VEGF, FGF10, FGF17, and TGF-β1 in a dose-dependent manner. Thus, TGF-α in BC could potentially be an important signal of carcinogenesis and metastasis. Macrophages in the nontumor tissue of BC may not be protective but could promote cancer metastasis.

Impact of human mesenchymal stromal cells on antifungal host response against Aspergillus fumigatus

Mesenchymal stromal cells (MSCs) are increasingly given as immunotherapy to hematopoietic stem cell transplant (HSCT) recipients with refractory graft-versus-host disease (GvHD). Whereas the immunosuppressive properties of MSCs seem to be beneficial in GvHD, there is, at the same time, major concern that MSCs increase the risk for infection. We therefore investigated the interplay of human MSCs with Aspergillus fumigatus and the impact of MSCs on different arms of the anti-Aspergillus host response in vitro. Although A. fumigatus hyphae increase mRNA levels of IL6 in MSCs, the extracellular availability of IL-6 and other pro-inflammatory cytokines remains unaffected. Human MSCs are able to phagocyte Aspergillus conidia, but phagocytosis of conidia is not associated with an alteration of the cytokine production by MSCs. In addition, human MSCs do not affect activation and function of A. fumigatus specific CD4+ T cells, and MSCs do not negatively impact the oxidative burst activity of phagocytes. Our in vitro data indicate that administration of human MSCs is not associated with a negative impact on the host response against A. fumigatus and that the fungus does not stimulate MSCs to increase the release of those cytokines which play a central role in the pathophysiology of GvHD.

Crocin reduces Aspergillus fumigatus-induced airway inflammation and NF-κB signal activation

Chronic obstructive pulmonary disease (COPD) is a chronic airway inflammation and its exacerbation is often accompanied by Aspergillus fumigatus (A. fumigatus) infection. Increasing evidences demonstrated the potent antioxidant and -inflammatory effects of crocin. However, the role of crocin in A. fumigatus-induced inflammation is still unknown. We aimed to evaluate the role of crocin in inflammation response induced by A. fumigatus in human bronchial epithelial cells and the possible mechanisms. BEAS-2B and NHBE cells were pretreated with crocin for 24 h, and then A. fumigatus conidia were added for 24 h. A. fumigatus treatment exhibited a significant higher TNF-α, IL-8, IL-6, and IL-1β level (P < 0.05), whereas crocin pretreatment significantly inhibited A. fumigatus induced the pro-inflammatory cytokines (P < 0.05). NF-κB inhibitor PDTC inhibited pro-inflammatory cytokines release triggered by A. fumigatus (P < 0.05). Furthermore, crocin suppressed A. fumigatus induced NF-κB p65 nuclear translocation, the phosphorylation of IKKα and IκBα, the degradation of IκBα and NF-κB reporter activity. Crocin pretreatment also resulted in an inhibition of A.fumigatus-induced ROS production (P < 0.05). Taken together, these results indicate that crocin may prevent A. fumigatus-induced inflammation through suppressing NF-κB signal pathway.