Fibrocytes Differ from Macrophages but Can Be Infected with HIV-1

Pravastatin prevents colitis-associated carcinogenesis by reducing CX3CR1high M2-like fibrocyte counts in the inflamed colon

Colorectal cancer (CRC) resulting from chronic inflammation is a crucial issue in patients with inflammatory bowel disease (IBD). Although many reports established that intestinal resident CX3CR1high macrophages play an essential role in suppressing intestinal inflammation, their function in colitis-related CRC remains unclear. In this study, we found that colonic CX3CR1high macrophages, which were positive for MHC-II, F4/80 and CD319, promoted colitis-associated CRC. They highly expressed Col1a1, Tgfb, II10, and II4, and were considered to be fibrocytes with an immunosuppressive M2-like phenotype. CX3CR1 deficiency led to reductions in the absolute numbers of CX3CR1high fibrocytes through increased apoptosis, thereby preventing the development of colitis-associated CRC. We next focused statins as drugs targeting CX3CR1high fibrocytes. Statins have been actively discussed for patients with IBD and reported to suppress the CX3CL1/CX3CR1 axis. Statin treatment after azoxymethane/dextran sulfate sodium-induced inflammation reduced CX3CR1high fibrocyte counts and suppressed colitis-associated CRC. Therefore, CX3CR1high fibrocytes represent a potential target for carcinogenesis-preventing therapy, and statins could be safe therapeutic candidates for IBD.

Recognition of HIV-1-infected fibrocytes lacking Nef-mediated HLA-B downregulation by HIV-1-specific T cells

Fibrocytes were reported to be host cells for HIV-1, but the immunological recognition of HIV-1-infected fibrocytes has not been studied. Here, we investigated the recognition of HIV-1-infected fibrocytes by HIV-1-specific CD8+ T cells. CD8+ T cells specific for five HIV-1 epitopes (HLA-A*24:02-restricted, HLA-B*52:01-restricted, and HLA-C*12:02-restricted epitopes) produced IFN-γ and expressed CD107a after coculture with HIV-1-infected fibrocytes. HIV-1-infected fibrocytes were effectively killed by HIV-1-specific CD8+ T cells. Although it is well known that HIV-1 Nef-mediated downregulation of HLA-A and HLA-B critically affects the T cell recognition of HIV-1-infected CD4+ T cells and HIV-1-infected macrophages, Nef downregulated HLA-A, but not HLA-B, in HIV-1-infected fibrocytes. These findings suggested that HIV-1-specific CD8+ T cells could recognize HIV-1-infected fibrocytes more strongly than HIV-1-infected CD4+ T cells or HIV-1-infected macrophages. HIV-1-infected fibrocytes were also recognized by HIV-1-specific HLA-DR-restricted T cells, indicating that HIV-1-infected fibrocytes can present HIV-1 epitopes to helper T cells. Collectively, these findings suggest that fibrocytes have an important role as antigen-presenting cells during HIV-1 infection. The present study demonstrates effective recognition of HIV-1-infected fibrocytes by HIV-1-specific T cells and suggests possible roles of fibrocytes in the induction and maintenance of HIV-1-specific T cells.

IMPORTANCE

Fibrocytes were identified as unique hematopoietic cells with the features of both macrophages and fibroblasts and were demonstrated to be host cells for HIV-1. However, T cell recognition of HIV-1-infected fibrocytes has not been studied. We investigated the recognition of HIV-1-infected fibrocytes by HIV-1-specific T cells. HIV-1-infected fibrocytes were effectively recognized and killed by CD8+ T cells specific for HIV-1 epitopes presented by HLA-A, HLA-B, or HLA-C and were recognized by HIV-1-specific HLA-DR-restricted CD4+ T cells. HIV-1 Nef-mediated downregulation of HLA-A and HLA-B was found in HIV-1-infected CD4+ T cells, whereas Nef did not downregulate HLA-B in HIV-1-infected fibrocytes. These results suggest that HIV-1-specific CD8+ T cells recognize HIV-1-infected fibrocytes more strongly than HIV-1-infected CD4+ T cells. The present study suggests the importance of fibrocytes in the induction and maintenance of HIV-1-specific T cells.

iPS cell-derived model to study the interaction between tissue macrophage and HIV-1

Despite effective antiretroviral therapy, HIV-1 persists in cells, including macrophages, which is an obstacle to cure. However, the precise role of macrophages in HIV-1 infection remains unclear because they reside in tissues that are not easily accessible. Monocyte-derived macrophages are widely used as a model in which peripheral blood monocytes are cultured and differentiated into macrophages. However, another model is needed because recent studies revealed that most macrophages in adult tissues originate from the yolk sac and fetal liver precursors rather than monocytes, and the embryonic macrophages possess a self-renewal (proliferating) capacity that monocyte-derived macrophages lack. Here, we show that human induced pluripotent stem cell-derived immortalized macrophage-like cells are a useful self-renewing macrophage model. They proliferate in a cytokine-dependent manner, retain macrophage functions, support HIV-1 replication, and exhibit infected monocyte-derived macrophage-like phenotypes, such as enhanced tunneling nanotube formation and cell motility, as well as resistance to a viral cytopathic effect. However, several differences are also observed between monocyte-derived macrophages and induced pluripotent stem cell-derived immortalized macrophage-like cells, most of which can be explained by the proliferation of induced pluripotent stem cell-derived immortalized macrophage-like cells. For instance, proviruses with large internal deletions, which increased over time in individuals receiving antiretroviral therapy, are enriched more rapidly in induced pluripotent stem cell-derived immortalized macrophage-like cells. Interestingly, inhibition of viral transcription by HIV-1-suppressing agents is more obvious in induced pluripotent stem cell-derived immortalized macrophage-like cells. Collectively, our present study proposes that the model of induced pluripotent stem cell-derived immortalized macrophage-like cells is suitable for mimicking the interplay between HIV-1 and self-renewing tissue macrophages, the newly recognized major population in most tissues that cannot be fully modeled by monocyte-derived macrophages alone.

Inhibitory and Stimulatory Effects of IL-32 on HIV-1 Infection

The proinflammatory cytokine IL-32 is elevated in the plasma and tissues of HIV-1–infected individuals. However, its significance in HIV-1 infection remains unclear because IL-32 inhibits and stimulates viral production in monocyte-derived macrophages (MDMs) and CD4+ T cells, respectively. In this study, we initially found that the inhibitory effect on human MDMs depends on SAMHD1, a dNTP triphosphohydrolase that inhibits viral reverse transcription. IL-32 increased the unphosphorylated active form of SAMHD1, which was consistent with the reduced expression of the upstream cyclin-dependent kinases. Indeed, IL-32 lost its anti–HIV-1 activity in MDMs when SAMHD1 was depleted. These results explain why IL-32 inhibits HIV-1 in MDMs but not CD4+ T cells, because SAMHD1 restricts HIV-1 in noncycling MDMs but not in cycling CD4+ T cells. Another unique feature of IL-32 is the induction of the immunosuppressive molecule IDO1, which is beneficial for HIV-1 infection. In this study, we found that IL-32 also upregulates other immunosuppressive molecules, including PD-L1, in MDMs. Moreover, IL-32 promoted the motility of MDMs, which potentially facilitates intercellular HIV-1 transmission. Our findings indicate that IL-32 has both the direct inhibitory effect on HIV-1 production in MDMs and the indirect stimulatory effects through phenotypic modulation of MDMs, and they suggest that the stimulatory effects may outweigh the inhibitory effect because the window for IL-32 to inhibit HIV-1 is relatively confined to SAMHD1-mediated reverse transcription suppression in the viral life cycle.

Novel Majeed Syndrome-Causing LPIN2 Mutations Link Bone Inflammation to Inflammatory M2 Macrophages and Accelerated Osteoclastogenesis

Objective

To identify novel heterozygous LPIN2 mutations in a patient with Majeed syndrome and characterize the pathomechanisms that lead to the development of sterile osteomyelitis.

Methods

Targeted genetic analysis and functional studies assessing monocyte responses, macrophage differentiation, and osteoclastogenesis were conducted to compare the pathogenesis of Majeed syndrome to interleukin‐1 (IL‐1)–mediated diseases including neonatal‐onset multisystem inflammatory disease (NOMID) and deficiency of the IL‐1 receptor antagonist (DIRA).

Results

A 4‐year‐old girl of mixed ethnic background presented with sterile osteomyelitis and elevated acute‐phase reactants. She had a 17.8‐kb deletion on the maternal LPIN2 allele and a splice site mutation, p.R517H, that variably spliced out exons 10 and 11 on the paternal LPIN2 allele. The patient achieved long‐lasting remission receiving IL‐1 blockade with canakinumab. Compared to controls, monocytes and monocyte‐derived M1‐like macrophages from the patient with Majeed syndrome and those with NOMID or DIRA had elevated caspase 1 activity and IL‐1β secretion. In contrast, lipopolysaccharide‐stimulated, monocyte‐derived, M2‐like macrophages from the patient with Majeed syndrome released higher levels of osteoclastogenic mediators (IL‐8, IL‐6, tumor necrosis factor, CCL2, macrophage inflammatory protein 1α/β, CXCL8, and CXCL1) compared to NOMID patients and healthy controls. Accelerated osteoclastogenesis in the patient with Majeed syndrome was associated with higher NFATc1 levels, enhanced JNK/MAPK, and reduced Src kinase activation, and partially responded to JNK inhibition and IL‐1 (but not IL‐6) blockade.

Conclusion

We report 2 novel compound heterozygous disease‐causing mutations in LPIN2 in an American patient with Majeed syndrome. LPIN2 deficiency drives differentiation of proinflammatory M2‐like macrophages and enhances intrinsic osteoclastogenesis. This provides a model for the pathogenesis of sterile osteomyelitis which differentiates Majeed syndrome from other IL‐1–mediated autoinflammatory diseases.

Establishment of bone marrow-derived M-CSF receptor-dependent self-renewing macrophages

Recent studies have revealed that tissue macrophages are derived from yolk sac precursors or fetal liver monocytes, in addition to bone marrow monocytes. The relative contribution of these cells to the tissue macrophage pool is not fully understood, but embryo-derived cells are supposed to be more important because of their capacity to self-renew. Here, we show the presence of adult bone marrow-derived macrophages that retain self-renewing capacity. The self-renewing macrophages were readily obtained by long-term culture of mouse bone marrow cells with macrophage colony-stimulating factor (M-CSF), a key cytokine for macrophage development. They were non-tumorigenic and proliferated in the presence of M-CSF in unlimited numbers. Despite several differences from non-proliferating macrophages, they retained many features of cells of the monocytic lineage, including the differentiation into dendritic cells or osteoclasts. Among the transcription factors involved in the self-renewal of embryonic stem cells, Krüppel-like factor 2 (KLF2) was strongly upregulated upon M-CSF stimulation in the self-renewing macrophages, which was accompanied by the downregulation of MafB, a transcription factor that suppresses KLF2 expression. Indeed, knockdown of KLF2 led to cell cycle arrest and diminished cell proliferation in the self-renewing macrophages. Our new cell model would be useful to unravel differences in phenotype, function, and molecular mechanism of proliferation among self-renewing macrophages with different origins.

Mucosal-associated invariant T (MAIT) cells provide B-cell help in vaccinated and subsequently SIV-infected Rhesus Macaques

Mucosal-associated invariant T (MAIT) cells help combat opportunistic infections. Thus, MAIT cells are of interest in HIV/SIV vaccination and infection. We investigated MAIT cell dynamics and function in rhesus macaque blood and bronchoalveolar lavage (BAL) following mucosal adenovirus (Ad)-SIV recombinant priming, intramuscular SIV envelope boosting and infection following repeated low-dose intravaginal SIV exposures. Increased frequencies of blood MAIT cells over the course of vaccination were observed, which were maintained even 12-weeks post-SIV infection. BAL MAIT cells only increased after the first Ad immunization. Vaccination increased MAIT cell levels in blood and BAL expressing the antiviral cytokine IFN-γ and TNF-α and the proliferation marker Ki67. Upon T cell-specific α-CD3, α-CD28 stimulation, MAIT cells showed a greater capacity to secrete cytokines/chemokines associated with help for B cell activation, migration and regulation compared to CD3⁺MR1⁻ cells. Culture of MAIT cell supernatants with B cells led to greater tissue like memory B cell frequencies. MAIT cell frequencies in blood and BAL correlated with SIV-specific antibody levels in rectal secretions and with SIV-specific tissue resident memory B cells. Overall, SIV vaccination influenced MAIT cell frequency and functionality. The potential for MAIT cells to provide help to B cells was evident during both vaccination and infection.

Fibrocytes, Wound Healing, and Corneal Fibrosis

Purpose

This review highlights the roles of fibrocytes—their origin, markers, regulation and functions—including contributions to corneal wound healing and fibrosis.

Methods

Literature review.

Results

Peripheral blood fibroblast-like cells, called fibrocytes, are primarily generated as mature collagen-producing cells in the bone marrow. They are likely derived from the myeloid lineage, although the exact precursor remains unknown. Fibrocytes are identified by a combination of expressed markers, such as simultaneous expression of CD34 or CD45 or CD11b and collagen type I or collagen type III. Fibrocytes migrate into the wound from the blood where they participate in pathogen clearance, tissue regeneration, wound closure and angiogenesis. Transforming growth factor beta 1 (TGF-β₁) and adiponectin induce expression of α-smooth muscle actin and extracellular matrix proteins through activation of Smad3 and adenosine monophosphate-activated protein kinase pathways, respectively. Fibrocytes are important contributors to the cornea wound healing response and there are several mechanisms through which fibrocytes contribute to fibrosis in the cornea and other organs, such as their differentiation into myofibroblasts, production of matrix metalloproteinase, secretion of tissue inhibitor of metalloproteinase, and release of TGF-β₁. In some tissues, fibrocytes may also contribute to the basement membrane regeneration and to the resolution of fibrosis.

Conclusions

New methods that block fibrocyte generation, fibrocyte migration, and their differentiation into myofibroblasts, as well as their production of matrix metalloproteinases, tissue inhibitor of metalloproteinase, and TGF-β₁, have therapeutic potential to reduce the accumulation of collagens, maintain tissue integrity and retard or prevent the development of fibrosis.

Expression of IL-34 correlates with macrophage infiltration and prognosis of diffuse large B-cell lymphoma

Objectives

Infiltration of macrophages through the tyrosine kinase receptor CSF1R is a poor prognosis factor in various solid tumors. Indeed, these tumors produce CSF1R ligand, macrophage colony‐stimulating factor (M‐CSF) or interleukin‐34 (IL‐34). However, the significance of these cytokines, particularly, the newly discovered IL‐34 in haematological malignancies, is not fully understood. We therefore analysed the role of IL‐34 in diffuse large B‐cell lymphoma (DLBCL), the most common subtype of malignant lymphoma.

Methods

We analysed formalin‐fixed paraffin‐embedded lymphoma tissues of 135 DLBCL patients for the expression of IL‐34 and the number of macrophages, and the survival of these patients. The expression of IL‐34 in DLBCL cell lines and the activity of IL‐34 to induce the migration of monocytic cells were also characterised.

Results

Several lymphoma tissues showed a clear IL‐34 signal, and such signal was detectable in 36% of patients. DLBCL cell lines also expressed IL‐34. Interestingly, the percentage of IL‐34⁺ patients in the activated B‐cell subtype was significantly higher than that in the germinal centre B‐cell subtype. More interestingly, IL‐34⁺ patients showed shorter survival periods and higher number of macrophages in lymphoma tissues. The recruitment of monocytes is likely the first step for the higher macrophage density in the IL‐34⁺ lymphoma tissues. Indeed, IL‐34 induced the migration of monocytic cells.

Conclusion

Our results raise the possibility that IL‐34 in lymphoma tissues of DLBCL patients recruits monocytes, leading to the higher number of macrophages in the tissues and poor prognosis of patients. IL‐34 may be an additional therapeutic target of DLBCL.

Increased SLAMF7high monocytes in myelofibrosis patients harboring JAK2V617F provide a therapeutic target of elotuzumab

Monocyte-derived fibrocytes recently garnered attention because the novel pathogenesis of myelofibrosis (MF), and suppression of fibrocyte differentiation by serum amyloid P remarkably improved MF. We previously revealed that human fibrocytes highly expressed signaling lymphocytic activation molecule F7 (SLAMF7) compared with macrophages and that SLAMF7^high monocytes in the peripheral blood (PB) of MF patients were significantly elevated relative to those in healthy controls (HCs). In this study, we evaluated SLAMF7^high monocyte percentage in the PB of HCs, myeloproliferative neoplasm (MPN) patients with MF, and MPN patients without MF by using a cross-sectional approach. We found that MPN patients with MF who harbored JAK2V617F had a significantly elevated SLAMF7^high monocyte percentage, which correlated positively with the JAK2V617F allele burden. In addition, the serum concentration of interleukin-1ra (IL-1ra) was significantly correlated with the SLAMF7^high monocyte percentage and JAK2V617F allele burden. These findings suggest that both SLAMF7^high monocytes and IL-1ra could be useful noninvasive markers of MF onset. Furthermore, the JAK2V617F allele burden of SLAMF7^high monocytes was significantly higher than that of SLAMF7^low monocytes and could be a potential target of elotuzumab (Elo), an anti-SLAMF7 antibody used for treating multiple myeloma. Elo independently inhibited differentiation of fibrocytes derived not only from HCs but also from MF patients in vitro. Elo also ameliorated MF and splenomegaly induced by romiplostim administration in humanized NOG mice. In conclusion, an increase of SLAMF7^high monocytes with higher JAK2V617F allele burden was associated with the onset of MF in MPN patients harboring JAK2V617F, and Elo could be a therapeutic agent for MPN patients with MF who harbor JAK2V617F.

Apolipoprotein E is an HIV-1-inducible inhibitor of viral production and infectivity in macrophages

Apolipoprotein E (ApoE) belongs to a class of cellular proteins involved in lipid metabolism. ApoE is a polymorphic protein produced primarily in macrophages and astrocytes. Different isoforms of ApoE have been associated with susceptibility to various diseases including Alzheimer's and cardiovascular diseases. ApoE expression has also been found to affect susceptibility to several viral diseases, including Hepatitis C and E, but its effect on the life cycle of HIV-1 remains obscure. In this study, we initially found that HIV-1 infection selectively up-regulated ApoE in human monocyte-derived macrophages (MDMs). Interestingly, ApoE knockdown in MDMs enhanced the production and infectivity of HIV-1, and was associated with increased localization of viral envelope (Env) proteins to the cell surface. Consistent with this, ApoE over-expression in 293T cells suppressed Env expression and viral infectivity, which was also observed with HIV-2 Env, but not with VSV-G Env. Mechanistic studies revealed that the C-terminal region of ApoE was required for its inhibitory effect on HIV-1 Env expression. Moreover, we found that ApoE and Env co-localized in the cells, and ApoE associated with gp160, the precursor form of Env, and that the suppression of Env expression by ApoE was cancelled by the treatment with lysosomal inhibitors. Overall, our study revealed that ApoE is an HIV-1-inducible inhibitor of viral production and infectivity in macrophages that exerts its anti-HIV-1 activity through association with gp160 Env via the C-terminal region, which results in subsequent degradation of gp160 Env in the lysosomes.

Myeloproliferative leukemia protein activation directly induces fibrocyte differentiation to cause myelofibrosis

Myelofibrosis (MF) may be caused by various pathogenic mechanisms such as elevation in circulating cytokine levels, cellular interactions and genetic mutations. However, the underlying mechanism of MF still remains unknown. Recent studies have revealed that fibrocytes, the spindle-shaped fibroblast-like hematopoietic cells, and the thrombopoietin (TPO)/myeloproliferative leukemia protein (MPL; TPO receptor) signaling pathway play a certain role in the development of MF. In the present study, we aimed to investigate the relationship between fibrocytes and MPL activation. We showed that TPO or a TPO receptor agonist directly induces fibrocyte differentiation using murine fibrocyte cell lines and a murine MF model. Conversely, elimination of macrophages expressing MPL by clodronate liposomes reversed the MF phenotype of the murine model, suggesting that fibrocyte differentiation induced by MPL activation contributes to the progression of MF. Furthermore, we revealed that SLAMF7^high MPL^high monocytes in human peripheral blood mononuclear cells were possible fibrocyte precursors and that these cells increased in number in MF patients not treated with ruxolitinib. Our findings confirmed a link between fibrocytes and the TPO/MPL signaling pathway, which could result in a greater understanding of the pathogenesis of MF and lead to the development of novel therapeutic interventions.

Are T cells the only HIV-1 reservoir?

Current antiretroviral therapies have improved the duration and quality of life of people living with HIV-1. However, viral reservoirs impede complete eradication of the virus. Although there are many strategies to eliminate infectious virus, the most actively pursued are latency reversing agents in conjunction with immune modulation. This strategy, known as “shock and kill”, has been tested primarily against the most widely recognized HIV-1 latent reservoir found in resting memory CD4+ T cells. This is in part because of the dearth of conclusive evidence about the existence of non-T cell reservoirs. Studies of non-T cell reservoirs have been difficult to interpret because of technical and biological issues that have hampered a better understanding. This review considers the current knowledge of non-T cell reservoirs, the challenges encountered in a better understanding of these populations, and their implications for HIV-1 cure research.