Masashi Kanayama

Hematopoietic stem cells (HSCs) play a pivotal role in the lifelong maintenance of hematopoiesis. However, heterogeneity and age-related alterations in HSC populations hinders accurate HSC analysis. Here, we show that bone marrow (BM) macrophage fragments that preferentially express F4/80 adhere to proliferative rather than dormant HSCs. The adhesion of macrophage fragments to proliferative HSCs occurred throughout the process of BM cell preparation in vitro. Consistently, proliferative HSCs express genes involved in the adhesion of macrophage fragments at higher levels than dormant HSCs. Notably, by using that as a benchmark, dormant HSCs can be easily identified as F4/80lowHSCs throughout their lifespan, thereby revealing that they retain considerable stemness and remain functional with aging. Collectively, we propose a novel and straightforward method for the rapid identification, isolation, and analysis of distinct HSC subpopulations, which will be helpful for a wide range of hematological studies and will provide insights into HSC biology.

Conventional dendritic cells (cDCs) regulate adaptive immunity. Although most cDCs are of myeloid origin (M-cDCs), some cDCs originate from pro–plasmacytoid DCs (pro-pDCs) via pDC-like cells [lymphoid cDCs (L-cDCs)]. Using lymphoid progenitor–tracking systems, we report tissue segregation, a unique differentiation pathway, and the functions of L-cDCs. Notably, L-cDC2s are predominantly distributed in barrier tissues such as the lungs and skin. Single-cell RNA-sequencing analysis revealed the enrichment of lymphocyte signature genes in L-cDCs. We identified lymphocyte-primed cDC precursors, which are distinct from pDC-like cells, as sources of L-cDCs. Compared with M-cDC2s, L-cDC2s weakly primed T cells under low-dose antigen stimulation and preferentially promoted T helper 2 (T _H 2) differentiation under sufficient antigenic stimulation. These results suggest the diverse developmental pathways of L-cDCs and imply the contribution of L-cDCs to tolerance and hyperresponses to T _H 2-related antigens in barrier tissues.

Emergency myelopoiesis (EM) is a hematopoietic response against systemic infections that quickly supplies innate immune cells. As lymphopoiesis is strongly suppressed during EM, the role of lymphocytes in that process has not received much attention. Here, we found that myeloid-like B cells (M-B cells), which express myeloid markers, emerge in the bone marrow (BM) after the induction of EM. M-B cells were mainly derived from pre-B cells and preferentially expressed IL-10, which directly stimulates hematopoietic progenitors to enhance their survival and myeloid-biased differentiation. Indeed, lacking IL-10 in B cells, blocking IL-10 in the BM with a neutralizing antibody, and deleting the IL-10 receptor in hematopoietic progenitors significantly suppressed EM, which failed to clear microbes in a cecal ligation and puncture model. Thus, a distinct B cell subset generated during infection plays a pivotal role in boosting EM, which suggests the on-demand reinforcement of EM by adaptive immune cells.

-Sca-1⁺c-Kit⁺ cells; LSKs), is not suitable for the analysis of hematopoietic responses under biological stresses with interferon (IFN) production. Lin^-Sca-1^-c-Kit⁺ cells (LKs), downstream progenitors of LSKs, acquire Sca-1 expression upon inflammation, which makes it impossible to distinguish between LSKs and LKs. As an alternative and stable marker even under such stresses, we identified CD86 by screening 180 surface markers. The analysis of infection/inflammation-triggered hematopoiesis on the basis of CD86 expression newly revealed urgent erythropoiesis producing stress-resistant RBCs and intact reconstitution capacity of LSKs, which could not be detected by conventional Sca-1-based analysis.

The size of immune-cell populations needs to be tightly regulated. Shinohara and colleagues demonstrate that intracellular and secreted osteopontin control the contraction and expansion of myeloid and lymphoid populations differently under infectious and autoimmune conditions. The balance of myeloid populations and lymphoid populations must be well controlled. Here we found that osteopontin (OPN) skewed this balance during pathogenic conditions such as infection and autoimmunity. Notably, two isoforms of OPN exerted distinct effects in shifting this balance through cell-type-specific regulation of apoptosis. Intracellular OPN (iOPN) diminished the population size of myeloid progenitor cells and myeloid cells, and secreted OPN (sOPN) increase the population size of lymphoid cells. The total effect of OPN on skewing the leukocyte population balance was observed as host sensitivity to early systemic infection with Candida albicans and T cell–mediated colitis. Our study suggests previously unknown detrimental roles for two OPN isoforms in causing the imbalance of leukocyte populations.

Osteopontin (OPN) is a protein, generally considered to play a pro‐tumorigenic role, whereas several reports have demonstrated the anti‐tumorigenic function of OPN during tumor development. These opposing anti‐ and pro‐tumorigenic functions are not fully understood. Here, we report that host‐derived OPN plays an anti‐tumorigenic role in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model and a TRAMP tumor transplant model. Tumor suppression mediated by OPN in Rag2^−/− mice suggests that OPN is dispensable in the adaptive immune response. We found that host‐derived OPN enhanced infiltration of natural killer (NK) cells into TRAMP tumors. The requirement of OPN in NK cell migration towards TRAMP cells was confirmed by an ex vivo cell migration assay. In contrast to TRAMP cells, in vivo B16 tumor development was not inhibited by OPN, and B16 tumors did not show OPN‐mediated cell recruitment. It is possible that low levels of chemokine expression by B16 cells do not allow OPN to enhance immune cell recruitment. In addition to demonstrating the anti‐tumorigenic role of OPN in TRAMP tumor development, this study also suggests that the contribution of OPN to tumor development depends on the type of tumor as well as the source and isoform of OPN.

Autoimmune diseases of the central nervous system (CNS), such as multiple sclerosis (MS), are characterized by infiltration of pathogenic immune cells in the CNS. Cells infiltrated in the CNS express pro-inflammatory molecules and cause demyelination. The direct impact of lung immune responses was not previously considered in the pathogenesis of CNS inflammation. However, it recently became clear that the lung acts as a hub organ of pathogenic T cells that are migrating to the CNS. More recent studies further showed that inflamed lung has a critical impact on autoimmune CNS inflammation. Here, we discuss the contribution of the lung in the pathogenesis of CNS autoimmune diseases based on recent reports.

Recruiting pathogenic T cells to the central nervous system (CNS) is a critical step during the development of experimental autoimmune encephalomyelitis (EAE). Here, we report that the absence of autophagy and microtubule-associated protein 1A/1B-light chain 3-associated phagocytosis significantly delayed the onset of EAE in Atg7 conditional knockout (Atg7 CKO) mice in myeloid cells. T-helper cell-cell priming appeared to be normal in the Atg7 CKO mice, but the mice showed significant accumulation of T_h17 cells in the lung. The data suggested that the stalling of T_h17 cells in the lung en route to the CNS caused the delay. The lung of Atg7 CKO mice, in which we previously demonstrated spontaneous mild inflammation, showed high expression of CCL20, a chemokine that attracts T_h17 cells. We have also shown that LPS intranasal instillation delayed EAE onset, suggesting that pulmonary inflammation has an impact on EAE development. Based on our data, therapeutic immunomodulation targeted to the lung, rather than systemically, might be a possible future option to treat multiple sclerosis.

Autophagy was initially characterized as a process to digest cellular components, including damaged cell organelles or unused proteins. However, later studies showed that autophagy plays an important role to protect hosts from microbial infections. Accumulating evidences showed the contribution of autophagy itself and autophagy-related proteins in the clearance of bacteria, virus, and parasites. A number of studies also revealed the molecular mechanisms by which autophagy is initiated and developed. Furthermore, it is now understood that some autophagy-related proteins are shared between two distinct processes; autophagy and LC3-associated phagocytosis (LAP). Thus, our understanding on autophagy has been greatly enhanced in the last decade. In contrast, roles of autophagy and autophagy-related proteins in fungal infections are still elusive relative to those in bacterial and viral infections. Based on limited numbers of reports, host responses including autophagy and autophagy-related proteins appear to significantly vary depending on invading fungal species. In this review, we discuss how autophagy and autophagy-related proteins are involved in antifungal immune responses based on recent discoveries.

The lung is constantly exposed to the outer environment; thus, it must maintain a state of immune ignorance or tolerance not to overrespond to harmless environmental stimuli. How cells in the lung control immune responses under nonpathogenic condition is not fully understood. In this study, we found that autophagy plays a critical role in the lung-specific immune regulation that prevents spontaneous inflammation. Autophagy in pulmonary myeloid cells plays a role in maintaining low burdens of environmental microbes in the lung, as well as in lowering mitochondrial reactive oxygen species production and preventing overresponse to TLR4 ligands in alveolar macrophages. Based on these mechanisms, we also found that intranasal instillation of antibiotics or an inhibitor of reactive oxygen species was efficient in preventing spontaneous pulmonary inflammation. Thus, autophagy in myeloid cells, particularly alveolar macrophages, is critical for inhibiting spontaneous pulmonary inflammation, and pulmonary inflammation caused by dysfunctional autophagy is pharmacologically prevented.