Immune Thrombocytopenia Revealing Enriched IgG-4 Peri-Renal Rosai-Dorfman Disease Successfully Treated with Rituximab: A Case Report and Literature Review.

Immune thrombocytopenia (ITP) is a rare autoimmune-mediated condition characterized by isolated thrombocytopenia (<100 G/L) after exclusion of other causes. Mostly primary, it is associated with hematological malignancy, autoimmune disorders, or infection in 20% of patients. It is exceptionally described in patients with histiocytosis, mostly in children (seven patients in literature). We report a case of a 69-year-old man with ITP leading to the diagnosis of histiocytosis. At ITP's diagnosis, the patient had elevated gamma-globulins leading to computed tomography showing bilateral peri-renal infiltration. The biopsy showed enriched IgG-4 peri-renal Rosai Dorfman disease with MAP2K1 mutation, although peri-renal infiltration is highly suggestive of Erdheim-Chester disease. This overlapping association was described in men with mutation in MAP2K1 gene. Macrophages are implicated in the pathophysiology of ITP in multiple ways, notably by the phagocytosis of opsonized platelets and their function of antigen-presenting cells able to stimulate autoreactive T cells. Histiocytic cells derivate from monocyte-macrophage lineage. Activation of macrophages in active histiocytosis is responsible for consequential platelet destruction in ITP associated histiocytosis. Finally, this case highlights a rare presentation of ITP revealing histiocytosis, both being efficiently treated with rituximab.

Pexidartinib treatment in Alexander disease model mice reduces macrophage numbers and increases glial fibrillary acidic protein levels, yet has minimal impact on other disease phenotypes

Background Alexander disease (AxD) is a rare neurodegenerative disorder that is caused by dominant mutations in the gene encoding glial fibrillary acidic protein (GFAP), an intermediate filament that is primarily expressed by astrocytes. In AxD, mutant GFAP in combination with increased GFAP expression result in astrocyte dysfunction and the accumulation of Rosenthal fibers. A neuroinflammatory environment consisting primarily of macrophage lineage cells has been observed in AxD patients and mouse models. Methods To examine if macrophage lineage cells could serve as a therapeutic target in AxD, GFAP knock-in mutant AxD model mice were treated with a colony-stimulating factor 1 receptor (CSF1R) inhibitor, pexidartinib. The effects of pexidartinib treatment on disease phenotypes were assessed. Results In AxD model mice, pexidartinib administration depleted macrophages in the CNS and caused elevation of GFAP transcript and protein levels with minimal impacts on other phenotypes including body weight, stress response activation, chemokine/cytokine expression, and T cell infiltration. Conclusions Together, these results highlight the complicated role that macrophages can play in neurological diseases and do not support the use of pexidartinib as a therapy for AxD.

Nanobody Nb6 fused with porcine IgG Fc as the delivering tag to inhibit porcine reproductive and respiratory syndrome virus replication in porcine alveolar macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly contagious virus that has led to enormous economic loss worldwide because of ineffective prevention and treatment. In view of their minimized size, high target specificity and affinity, nanobodies have been extensively investigated as diagnostic tools and treatments of many diseases. Previously, a PRRSV Nsp9-specific nanobody (Nb6) was identified as a PRRSV replication inhibitor. When it was fused with cell-penetrating peptide (CPP) TAT, Nb6-TAT could enter the cells for PRRSV suppression. However, delivery of molecules by CPP lack cell specificity and have a short duration of action. PRRSV has a tropism for monocyte/macrophage lineage, which expresses high levels of Fcγ receptors. Herein, we designed a nanobody containing porcine IgG Fc (Fcγ) to inhibit PRRSV replication in PRRSV permissive cells. Fcγ fused Nb6 chimeric antibody (Nb6-pFc) was assembled into a dimer with interchain disulfide bonds and expressed in a Pichia pastoris system. The results show that Nb6-pFc exhibits a well-binding ability to recombinant Nsp9 or PRRSV-encoded Nsp9 and that FcγR-mediated endocytosis of Nb6-pFc into porcine alveolar macrophages (PAM) was in a dose-dependent manner. Nb6-pFc can inhibit PRRSV infection efficiently not only by binding with Nsp9 but also by upregulating proinflammatory cytokine production in PAM. Together, this study proposes the design of a porcine IgG Fc-fused nanobody that can enter PRRSV susceptible PAM via FcγR-mediated endocytosis and inhibit PRRSV replication. This research reveals that nanobody-Fcγ chimeric antibodies might be effective for the control and prevention of monocyte/macrophage lineage susceptible pathogeneses.

Two macrophages, osteoclasts and microglia: from development to pleiotropy

Tissue-resident macrophages are highly specialized to their tissue-specific microenvironments, activated by various inflammatory signals and modulated by genetic and environmental factors. Osteoclasts and microglia are distinct tissue-resident cells of the macrophage lineage in bone and brain that are responsible for pathological changes in osteoporosis and Alzheimer’s disease (AD), respectively. Osteoporosis is more frequently observed in individuals with AD compared to the prevalence in general population. Diagnosis of AD is often delayed until underlying pathophysiological changes progress and cause irreversible damages in structure and function of brain. As such earlier diagnosis and intervention of individuals at higher risk would be indispensable to modify clinical courses. Pleiotropy is the phenomenon that a genetic variant affects multiple traits and the genetic correlation between two traits could suggest a shared molecular mechanism. In this review, we discuss that the Pyk2-mediated actin polymerization pathway in osteoclasts and microglia in bone and brain, respectively, is the horizontal pleiotropic mediator of shared risk factors for osteoporosis and AD.

Monocyte/Macrophage Lineage Cells From Fetal Erythromyeloid Progenitors Orchestrate Bone Remodeling and Repair

A third of the population sustains a bone fracture, and the pace of fracture healing slows with age. The slower pace of repair is responsible for the increased morbidity in older individuals who sustain a fracture. Bone healing progresses through overlapping phases, initiated by cells of the monocyte/macrophage lineage. The repair process ends with remodeling. This last phase is controlled by osteoclasts, which are bone-specific multinucleated cells also of the monocyte/macrophage lineage. The slower rate of healing in aging can be rejuvenated by macrophages from young animals, and secreted proteins from macrophage regulate undifferentiated mesenchymal cells to become bone-forming osteoblasts. Macrophages can derive from fetal erythromyeloid progenitors or from adult hematopoietic progenitors. Recent studies show that fetal erythromyeloid progenitors are responsible for the osteoclasts that form the space in bone for hematopoiesis and the fetal osteoclast precursors reside in the spleen postnatally, traveling through the blood to participate in fracture repair. Differences in secreted proteins between macrophages from old and young animals regulate the efficiency of osteoblast differentiation from undifferentiated mesenchymal precursor cells. Interestingly, during the remodeling phase osteoclasts can form from the fusion between monocyte/macrophage lineage cells from the fetal and postnatal precursor populations. Data from single cell RNA sequencing identifies specific markers for populations derived from the different precursor populations, a finding that can be used in future studies. Here, we review the diversity of macrophages and osteoclasts, and discuss recent finding about their developmental origin and functions, which provides novel insights into their roles in bone homeostasis and repair.

Characterization of the Tumor Microenvironment of Neurofibromatosis Type I Plexiform Neurofibromas

Background/Objective: Neurofibromatosis type 1 (NF1) is a cancer predisposition syndrome caused by mutations in the NF1 tumor suppressor gene. Patients with NF1 develop tumors of the peripheral nervous system called plexiform neurofibromas (PNs). These histopathologically complex tumors are composed of various immune and inflammatory cells. Mast cells have previously been identified as one key immune cell lineage underpinning PN initiation and progression, however new technologies leveraging RNA-sequencing (RNAseq) allow for the broad and systematic characterization of the PN tumor microenvironment. Here we utilized these tools to delineate PN cellular composition. Methods: RNA seq was performed on murine wild type (n=6) and PN (n=6) tissues. We utilized CIBERSORT to profile the cellular constituents of the PN microenvironment. CIBERSORT is a deconvolution method that uses a reference matrix to estimate the relative proportions of various cell types. Statistical analyses were performed on cell lineage subtypes delineated by CIBERSORT. We further performed a Gene Set Enrichment Analysis (GSEA) to identify which pathways and cytokines might be upregulated in PNs. Results: Using a murine reference matrix, the macrophage lineage, M0 (p = 0.072), M1 (p = 0.1), were upregulated in PNs (n=6) compared to WT (n=6). A human reference matrix showed M2 (p=0.025) to be upregulated in PNs. GSEA showed IL-1, IL-6, IL-8, TNF and Type I IFN and cytokine secretion to be upregulated in PNs compared to WT. Conclusion: Macrophages were among the most upregulated components of the NF1 tumor microenvironment and upregulation of IL-1, IL-6, IL-8, TNF and Type I IFN production may be contributing to inflammation that is critical in the initiation and progression of PNs. Scientific/Clinical/Policy Impact and Implications: Pharmacotherapies that can target the macrophage lineage and/or aforementioned cytokines may have utility in the treatment of PNs. Further studies are necessary to evaluate this hypothesis.

Repression of lysosomal transcription factors Tfeb and Tfe3 is essential for the development and function of microglia

SUMMARYAs the primary phagocytic cells of the central nervous system, microglia exquisitely regulate their lysosomal activity to facilitate brain development and homeostasis. However, mechanisms that coordinate lysosomal activity with microglia development, migration, and function remain unclear. Here we show that embryonic macrophages require the lysosomal GTPase RagA and the GTPase-activating protein Folliculin (Flcn) for colonization of the brain. Mutants lacking RagA and Flcn have nearly identical phenotypes, suggesting that RagA and Flcn act in concert in developing microglia. Furthermore, we demonstrate that RagA and Flcn repress the key lysosomal transcription factor Tfeb, and its homologs Tfe3a and Tfe3b, in macrophages. Accordingly, defects in rraga mutants can be restored by simultaneous mutations in tfeb, tfe3a, and tfe3b, and overexpression of tfe3b in the macrophage lineage recapitulates the major defects observed in rraga and flcn mutants. Collectively, our data define a lysosomal regulatory circuit that is essential for early development of microglia.