Fasting-Refeeding Impacts Immune Cell Dynamics and Mucosal Immune Responses.

Nutritional status potentially influences immune responses; however, how nutritional signals regulate cellular dynamics and functionality remains obscure. Herein, we report that temporary fasting drastically reduces the number of lymphocytes by ∼50% in Peyer's patches (PPs), the inductive site of the gut immune response. Subsequent refeeding seemingly restored the number of lymphocytes, but whose cellular composition was conspicuously altered. A large portion of germinal center and IgA+ B cells were lost via apoptosis during fasting. Meanwhile, naive B cells migrated from PPs to the bone marrow during fasting and then back to PPs during refeeding when stromal cells sensed nutritional signals and upregulated CXCL13 expression to recruit naive B cells. Furthermore, temporal fasting before oral immunization with ovalbumin abolished the induction of antigen-specific IgA, failed to induce oral tolerance, and eventually exacerbated food antigen-induced diarrhea. Thus, nutritional signals are critical in maintaining gut immune homeostasis.

Arf1 and Arf6 Synergistically Maintain Survival of T Cells during Activation.

ADP-ribosylation factor (Arf) family consisting of six family members, Arf1-Arf6, belongs to Ras superfamily and orchestrates vesicle trafficking under the control of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins. It is well established that brefeldin A, a potent inhibitor of ArfGEFs, blocks cytokine secretion from activated T cells, suggesting that the Arf pathway plays important roles in T cell functions. In this study, because Arf1 and Arf6 are the best-characterized members among Arf family, we established T lineage-specific Arf1-deficient, Arf6-deficient, and Arf1/6 double-deficient mice to understand physiological roles of the Arf pathway in the immune system. Contrary to our expectation, Arf deficiency had little or no impact on cytokine secretion from the activated T cells. In contrast, the lack of both Arf1 and Arf6, but neither Arf1 nor Arf6 deficiency alone, rendered naive T cells susceptible to apoptosis upon TCR stimulation because of imbalanced expression of Bcl-2 family members. We further demonstrate that Arf1/6 deficiency in T cells alleviates autoimmune diseases like colitis and experimental autoimmune encephalomyelitis, whereas Ab response under Th2-polarizing conditions is seemingly normal. Our findings reveal an unexpected role for the Arf pathway in the survival of T cells during TCR-induced activation and its potential as a therapeutic target in the autoimmune diseases.

Lymph Node Stromal Cells: Diverse Meshwork Structures Weave Functionally Subdivided Niches.

Lymph nodes (LNs) are secondary lymphoid organs that function as the first line of defense against invasive foreign substances. Within the LNs, different types of immune cells are strategically localized to induce immune responses efficiently. Such a sophisticated tissue structure is a complex of functionally specialized niches, constructed by a variety of fibroblastic stromal cells. Elucidating the characteristics and functions of the niches and stromal cells will facilitate comprehension of the immune response induced in the LNs. Three recent studies offered novel insights into specialized stromal cells. In our discussion of these surprisingly diverse stromal cells, we will integrate information from these studies to improve knowledge about the structure and niches of LN.

Transdermal entry of yeast components elicits transient B cell-associated responses in skin-draining lymph nodes.

Immune responses to non-pathogenic yeasts induced within the draining lymph node remain to be understood. In this study, we have investigated the changes in lymphocytes and their activity in skin-draining lymph nodes in response to transdermally injected zymosan (component of the yeast cell wall). Zymosan elicited the transient increase of B cell number and activation status without affecting the capacity for proliferation. The increased B cell content in the regional lymph nodes was likely due to the reduction of B cell egress from the tissue and in part the increase of homing from the circulation. Zymosan also upregulated the inflammatory cytokines, such as IL-1ß, IL-6, IL-12, and IFNγ, regulatory cytokines IL-10 and TGFß, and lymphoid chemokine CXCL13. Among these, the expression of IL-12 and IL-10 was markedly high in B cells. Altogether, these findings demonstrate a unique B cell-associated response to non-pathogenic yeast component in the draining lymph nodes. This will provide insights into the clinical and healthcare applications of non-pathogenic beneficial microbes.

Essential Role of Canonical NF-κB Activity in the Development of Stromal Cell Subsets in Secondary Lymphoid Organs.

Organized tissue structure in the secondary lymphoid organs (SLOs) tightly depends on the development of fibroblastic stromal cells (FSCs) of mesenchymal origin; however, the mechanisms of this relationship are poorly understood. In this study, we specifically inactivated the canonical NF-κB pathway in FSCs in vivo by conditionally inducing IκBα mutant in a Ccl19-IκBSR mouse system in which NF-κB activity is likely to be suppressed in fetal FSC progenitors. Given that NF-κB activation in fetal FSCs is essential for SLO development, the animals were expected to lack SLOs. However, all SLOs were preserved in Ccl19-IκBSR mice. Instead, the T cell area was severely disturbed by the lack of CCL21-expressing FSCs, whereas the follicles and associated FSC networks were formed. Fate mapping revealed that IκBSR-expressing cells constituted only a small fraction of stromal compartment outside the follicles. Taken together, our findings indicate an essential role of the canonical NF-κB pathway activity in the development of three FSC subsets common to SLOs and suggest transient or stochastic CCL19 expression in FSC progenitors and a compensatory differentiation program of follicular FSCs.

Visualizing the Rapid and Dynamic Elimination of Allogeneic T Cells in Secondary Lymphoid Organs.

Allogeneic organ transplants are rejected by the recipient immune system within several days or weeks. However, the rejection process of allogeneic T (allo-T) cells is poorly understood. In this study, using fluorescence-based monitoring and two-photon live imaging in mouse adoptive transfer system, we visualized the fate of allo-T cells in the in vivo environment and showed rapid elimination in secondary lymphoid organs (SLOs). Although i.v. transferred allo-T cells efficiently entered host SLOs, including lymph nodes and the spleen, ∼70% of the cells had disappeared within 24 h. At early time points, allo-T cells robustly migrated in the T cell area, whereas after 8 h, the numbers of arrested cells and cell fragments were dramatically elevated. Apoptotic breakdown of allo-T cells released a large amount of cell debris, which was efficiently phagocytosed and cleared by CD8+ dendritic cells. Rapid elimination of allo-T cells was also observed in nu/nu recipients. Depletion of NK cells abrogated allo-T cell reduction only in a specific combination of donor and recipient genetic backgrounds. In addition, F1 hybrid transfer experiments showed that allo-T cell killing was independent of the missing-self signature typically recognized by NK cells. These suggest the presence of a unique and previously uncharacterized modality of allorecognition by the host immune system. Taken together, our findings reveal an extremely efficient and dynamic process of allogeneic lymphocyte elimination in SLOs, which could not be recapitulated in vitro and is distinct from the rejection of solid organ and bone marrow transplants.

Extensively re-organized systemic lymph nodes provide a feasible environment for self-reactivity in lupus-prone NZB × NZW F1 mice.

Lymphadenopathy is a frequently observed symptom in systemic lupus erythematosus, although the immunological role of lymph nodes (LNs) in systemic autoimmunity remains largely unknown. Here, we performed comprehensive and systematic analyses of LNs in lupus-prone NZB × NZW F1 (BWF1) mice, demonstrating extensive tissue re-organization of the systemic LNs with follicular expansion, hyper germinal center (GC) formation, atrophy of the paracortical T-cell area and expansion of the medulla in aged BWF1 mice bearing glomerulonephritis. The proportion of B cells was significantly increased in these reactive LNs but not in the spleen, and lymphocyte subsets involved in antibody production, i.e. GC B cells, follicular helper T cells and plasma cells, were elevated. Draining LNs of the affected organs, such as the renal and cervical nodes, showed enhanced tissue re-organization and accumulation of effector lymphocytes, suggesting the presence of a positive feedback loop of regional responses. LN cells isolated from disease-bearing animals produced anti-DNA antibody, indicating activation of autoreactive lymphocytes in situ. The substantial development of disease and LN alterations in mice that received a splenectomy at a young age points to the importance of other secondary lymphoid organs, most likely LNs, for the progression of autoimmune responses independent of the spleen. Taken together, our findings highlight the value of taking LN alterations and activities into consideration for understanding the pathogenesis of systemic autoimmunity.

Autotaxin produced by stromal cells promotes LFA-1-independent and Rho-dependent interstitial T cell motility in the lymph node paracortex.

T cells exhibit high-speed migration within the paracortical T zone of lymph nodes (LNs) as they scan cognate Ags displayed by dendritic cells in the tissue microenvironment supported by the network of stromal cells. Although intranodal T cell migration is controlled in part by chemokines and LFA-1/ICAM-1, the mechanisms underlying their migratory activity independent of these factors remain to be elucidated. In this study, we show that LN stromal cells constitutively express autotaxin (ATX), an ectoenzyme that is important for the generation of lysophosphatidic acid (LPA). Importantly, CCL21(+) stromal cells in the T zone produced and immobilized ATX on their cell surface. Two-photon imaging using LN tissue slices revealed that pharmacological inhibition of ATX or LPA receptors significantly reduced T cell migration, and this was further exacerbated by blockage of Gαi signaling or LFA-1. Therefore, T cell motility mediated by the ATX-LPA axis was independent of Gαi and LFA-1. LPA induced slow intermittent movement of T cells in vitro in a LFA-1-independent manner and enhanced CCL21-induced migration. Moreover, LPA and CCL21 cooperatively augmented RhoA activity in T cells, which was necessary for efficient intranodal T cell migration via the downstream ROCK-myosin II pathway. Taken together, T zone stromal cells control optimal migratory behavior of T cells via multiple signaling cues mediated by chemokines and ATX/LPA.

Dendritic cells regulate high-speed interstitial T cell migration in the lymph node via LFA-1/ICAM-1.

T lymphocytes vigorously migrate within the paracortex of lymph nodes (LNs) in search of cognate Ags that are presented by dendritic cells (DCs). However, the mechanisms that support T cells to exert the highest motility in a densely packed LN microenvironment are not fully understood. Two-photon microscopy using LN tissue slices revealed that LFA-1 and ICAM-1 were required for high-velocity migration (>10 µm/min) with relatively straight movement. Importantly, ICAM-1 expressed by myeloid lineages, most likely DCs, but not stromal cells or lymphocytes, was sufficient to support the high-velocity migration. Visualizing DCs in the LN from CD11c-EYFP mice showed that T cells traveled over thin dendrites and the body of DCs. Interestingly, DCs supported T cell motility in vitro in chemokine- and ICAM-1-dependent manners. Moreover, an acute lymphopenic environment in the LN significantly increased LFA-1 dependency for T cell migration, indicating that lymphocyte density modulates the use of LFA-1. Therefore, our results indicate that LFA-1/ICAM-1-dependent interactions between T cells and DCs play a crucial role not only in supporting firm arrest during Ag recognition but also in facilitating the Ag scanning processes.

Structural basis for mutual relief of the Rac guanine nucleotide exchange factor DOCK2 and its partner ELMO1 from their autoinhibited forms.

DOCK2, a hematopoietic cell-specific, atypical guanine nucleotide exchange factor, controls lymphocyte migration through ras-related C3 botulinum toxin substrate (Rac) activation. Dedicator of cytokinesis 2-engulfment and cell motility protein 1 (DOCK2•ELMO1) complex formation is required for DOCK2-mediated Rac signaling. In this study, we identified the N-terminal 177-residue fragment and the C-terminal 196-residue fragment of human DOCK2 and ELMO1, respectively, as the mutual binding regions, and solved the crystal structure of their complex at 2.1-Šresolution. The C-terminal Pro-rich tail of ELMO1 winds around the Src-homology 3 domain of DOCK2, and an intermolecular five-helix bundle is formed. Overall, the entire regions of both DOCK2 and ELMO1 assemble to create a rigid structure, which is required for the DOCK2•ELMO1 binding, as revealed by mutagenesis. Intriguingly, the DOCK2•ELMO1 interface hydrophobically buries a residue which, when mutated, reportedly relieves DOCK180 from autoinhibition. We demonstrated that the ELMO-interacting region and the DOCK-homology region 2 guanine nucleotide exchange factor domain of DOCK2 associate with each other for the autoinhibition, and that the assembly with ELMO1 weakens the interaction, relieving DOCK2 from the autoinhibition. The interactions between the N- and C-terminal regions of ELMO1 reportedly cause its autoinhibition, and binding with a DOCK protein relieves the autoinhibition for ras homolog gene family, member G binding and membrane localization. In fact, the DOCK2•ELMO1 interface also buries the ELMO1 residues required for the autoinhibition within the hydrophobic core of the helix bundle. Therefore, the present complex structure reveals the structural basis by which DOCK2 and ELMO1 mutually relieve their autoinhibition for the activation of Rac1 for lymphocyte chemotaxis.

DOCK8 is a Cdc42 activator critical for interstitial dendritic cell migration during immune responses.

To migrate efficiently through the interstitium, dendritic cells (DCs) constantly adapt their shape to the given structure of the extracellular matrix and follow the path of least resistance. It is known that this amoeboid migration of DCs requires Cdc42, yet the upstream regulators critical for localization and activation of Cdc42 remain to be determined. Mutations of DOCK8, a member of the atypical guanine nucleotide exchange factor family, causes combined immunodeficiency in humans. In the present study, we show that DOCK8 is a Cdc42-specific guanine nucleotide exchange factor that is critical for interstitial DC migration. By generating the knockout mice, we found that in the absence of DOCK8, DCs failed to accumulate in the lymph node parenchyma for T-cell priming. Although DOCK8-deficient DCs migrated normally on 2-dimensional surfaces, DOCK8 was required for DCs to crawl within 3-dimensional fibrillar networks and to transmigrate through the subcapsular sinus floor. This function of DOCK8 depended on the DHR-2 domain mediating Cdc42 activation. DOCK8 deficiency did not affect global Cdc42 activity. However, Cdc42 activation at the leading edge membrane was impaired in DOCK8-deficient DCs, resulting in a severe defect in amoeboid polarization and migration. Therefore, DOCK8 regulates interstitial DC migration by controlling Cdc42 activity spatially.

A battle between two biological singularities: Immune response vs. cancer.

In a post-growth multicellular organism, the phenomenon in which a small number of rare cells can be the starting point for inducing a dramatic change in the entire system is considered a "biological singularity." The immune response and cancer can be regarded as singularity phenomena in mammals, but their nature is fundamentally different. The immune response is considered a "programmed" singularity, whereas cancer is an "unprogrammed" singularity. These two systems perpetually engage in a cycle of attack and defense within the organism. The outcome is depending on the wining system, which determines whether the individual experiences a state resembling light or darkness. However, the overall mechanism of the competition remains unclear and is expected to be elucidated with future innovations in bioimaging technologies. Immune checkpoint blockade therapy is a means by which the two singularity balances can be artificially manipulated; therefore, mechanistic insight is necessary for cancer treatment strategies. Altogether, these findings provide a different perspective crucial for understanding the behavior of dynamic cell populations in multicellular organisms.

Sublingual immune cell clusters and dendritic cell distribution in the oral cavity.

The oral mucosa is the first line of defense against pathogenic bacteria and plays a vital role in maintaining tolerance to food antigens and commensal bacteria. We used CD11c reporter mice to visualize dendritic cells (DCs), a key immune cell population, in the oral cavity. We identified differences in DC density in each oral tissue region. Sublingual immune cell clusters (SLICs) extended from the lamina propria to the epithelium, where DCs and T cells resided in close contact with each other and innate lymphoid cells (ILCs). Targeted in situ photolabeling revealed that the SLICs comprised mostly of CD11c+CD11b+ DCs and were enriched for cDC1s and Langerhans cells. Although the frequency of T cell subsets was similar within and outside the SLICs, tissue resident memory T cells were significantly enriched within the clusters and cluster size increased in response to inflammation. Collectively, we found that SLICs form a unique microenvironment that facilitates T cell-DC interactions in the steady state and during inflammation. Since the oral mucosa is an important target for needle-free vaccination and sublingual immunotherapy to induce tolerogenic responses, the novel insight into the localized immunoregulation provided in this study may accelerate the development of these approaches.

Mst1 controls lymphocyte trafficking and interstitial motility within lymph nodes.

The regulation of lymphocyte adhesion and migration plays crucial roles in lymphocyte trafficking during immunosurveillance. However, our understanding of the intracellular signalling that regulates these processes is still limited. Here, we show that the Ste20-like kinase Mst1 plays crucial roles in lymphocyte trafficking in vivo. Mst1(-/-) lymphocytes exhibited an impairment of firm adhesion to high endothelial venules, resulting in an inefficient homing capacity. In vitro lymphocyte adhesion cascade assays under physiological shear flow revealed that the stopping time of Mst1(-/-) lymphocytes on endothelium was markedly reduced, whereas their L-selectin-dependent rolling/tethering and transition to LFA-1-mediated arrest were not affected. Mst1(-/-) lymphocytes were also defective in the stabilization of adhesion through alpha4 integrins. Consequently, Mst1(-/-) mice had hypotrophic peripheral lymphoid tissues and reduced marginal zone B cells and dendritic cells in the spleen, and defective emigration of single positive thymocytes. Furthermore, Mst1(-/-) lymphocytes had impaired motility over lymph node-derived stromal cells and within lymph nodes. Thus, our data indicate that Mst1 is a key enzyme involved in lymphocyte entry and interstitial migration.

Yin and yang roles of B lymphocytes in solid tumors: Balance between antitumor immunity and immune tolerance/immunosuppression in tumor-draining lymph nodes.

The role of B cells in antitumor immunity has been reported to be either promotive or suppressive, but the specific mechanism remains to be comprehensively understood. However, this complicated situation likely depends on the temporal and spatial relationship between the developing tumor and B cells that recognize tumor antigens. Unlike responses against microbial or pathogenic infections, tumor cells are derived from autologous cells that have mutated and become aberrant; thus, elimination by the adaptive immune system is essentially inefficient. If tumor cells can evade immune attack at an early stage, non-destructive responses, such as tolerance and immunosuppression, are established over time. In tumor-draining lymph nodes (TDLNs), tumor antigen-reactive B cells potentially acquire immunoregulatory phenotypes and contribute to an immunosuppressive microenvironment. Therefore, triggering and enhancing antitumor responses by immunotherapies require selective control of these regulatory B cell subsets in TDLNs. In contrast, B cell infiltration and formation of tertiary lymphoid structures in tumors are positively correlated with therapeutic prognosis, suggesting that tumor antigen-specific activation of B cells and antibody production are advantageous for antitumor immunity in mid- to late-stage tumors. Given that the presence of B cells in tumor tissues may reflect the ongoing antitumor response in TDLNs, therapeutic induction and enhancement of these lymphocytes are expected to increase the overall effectiveness of immunotherapy. Therefore, B cells are promising targets, but the spatiotemporal balance of the subsets that exhibit opposite characteristics, that is, the protumor or antitumor state in TDLNs, should be understood, and strategies to separately control their functions should be developed to maximize the clinical outcome.

Endogenous CCL21-Ser deficiency reduces B16-F10 melanoma growth by enhanced antitumor immunity.

The chemokine CCL21 regulates immune and cancer cell migration through its receptor CCR7. The Ccl21a gene encodes the isoform CCL21-Ser, predominantly expressed in the thymic medulla and the secondary lymphoid tissues. This study examined the roles of CCL21-Ser in the antitumor immune response in Ccl21a-knockout (KO) mice. The Ccl21a-KO mice showed significantly decreased growth of B16-F10 and YUMM1.7 melanomas and increased growth of MC38 colon cancer, despite no significant difference in LLC lung cancer and EO771 breast cancer. The B16-F10 tumor in Ccl21a-KO mice showed melanoma-specific activated CD8+ T cell and NK cell infiltration and higher Treg counts than wild-type mice. B16-F10 tumors in Ccl21a-KO mice showed a reduction in the positive correlation between the ratio of regulatory T cells (Tregs) to activated CD8+ T cells and tumor weight. In Ccl21a-KO tumor, the intratumoral Tregs showed lower co-inhibitory receptors TIM-3 and TIGIT. Taken together, these results suggest that endogenous CCL21-Ser supports melanoma growth in vivo by maintaining Treg function and suppressing antitumor immunity by CD8+ T cells.

Rap1 controls lymphocyte adhesion cascade and interstitial migration within lymph nodes in RAPL-dependent and -independent manners.

The small GTPase Rap1 and its effector RAPL regulate lymphocyte adhesion and motility. However, their precise regulatory roles in the adhesion cascade preceding entry into lymph nodes and during interstitial migration are unclear. Here, we show that Rap1 is indispensably required for the chemokine-triggered initial arrest step of rolling lymphocytes through LFA-1, whereas RAPL is not involved in rapid arrest. RAPL and talin play a critical role in stabilizing lymphocyte arrest to the endothelium of blood vessels under flow or to the high endothelial venules of peripheral lymph nodes in vivo. Further, mutagenesis and peptide studies suggest that release of a trans-acting restraint from the beta2 cytoplasmic region of LFA-1 is critical for Rap1-dependent initial arrest. Rap1 or RAPL deficiency severely impaired lymphocyte motility over lymph node stromal cells in vitro, and RAPL deficiency impaired high-velocity directional movement within lymph nodes. These findings reveal the several critical steps of Rap1, which are RAPL-dependent and -independent, in lymphocyte trafficking.

Graded attenuation of TCR signaling elicits distinct autoimmune diseases by altering thymic T cell selection and regulatory T cell function.

Mice with a mutation of the zeta-associated protein of 70 kDa gene (skg mutation) are genetically prone to develop autoimmune arthritis, depending on the environment. In a set of mice with the mutation, the amount of zeta-associated protein of 70 kDa protein as well as its tyrosine phosphorylation upon TCR stimulation decreased from +/+, skg/+, skg/skg, to skg/- mice in a stepwise manner. The reduction resulted in graded alterations of thymic positive and negative selection of self-reactive T cells and Foxp3(+) natural regulatory T cells (Tregs) and their respective functions. Consequently, skg/- mice spontaneously developed autoimmune arthritis even in a microbially clean environment, whereas skg/skg mice required stimulation through innate immunity for disease manifestation. After Treg depletion, organ-specific autoimmune diseases, especially autoimmune gastritis, predominantly developed in +/+, at a lesser incidence in skg/+, but not in skg/skg BALB/c mice, which suffered from other autoimmune diseases, especially autoimmune arthritis. In correlation with this change, gastritis-mediating TCR transgenic T cells were positively selected in +/+, less in skg/+, but not in skg/skg BALB/c mice. Similarly, on the genetic background of diabetes-prone NOD mice, diabetes spontaneously developed in +/+, at a lesser incidence in skg/+, but not in skg/skg mice, which instead succumbed to arthritis. Thus, the graded attenuation of TCR signaling alters the repertoire and the function of autoimmune T cells and natural Tregs in a progressive manner. It also changes the dependency of disease development on environmental stimuli. These findings collectively provide a model of how genetic anomaly of T cell signaling contributes to the development of autoimmune disease.

Tas2R signaling enhances mouse neutrophil migration via a ROCK-dependent pathway.

Type-2 bitter taste receptors (Tas2Rs) are a large family of G protein-coupled receptors that are expressed in the oral cavity and serve to detect substances with bitter tastes in foods and medicines. Recent evidence suggests that Tas2Rs are also expressed extraorally, including in immune cells. However, the role of Tas2Rs in immune cells remains controversial. Here, we demonstrate that Tas2R126, Tas2R135, and Tas2R143 are expressed in mouse neutrophils, but not in other immune cells such as macrophages or T and B lymphocytes. Treatment of bone marrow-derived neutrophils from wild-type mice with the Tas2R126/143 agonists arbutin and d-salicin led to enhanced C-X-C motif chemokine ligand 2 (CXCL2)-stimulated migration in vitro, but this response was not observed in neutrophils from Tas2r126/135/143-deficient mice. Enhancement of CXCL2-stimulated migration by Tas2R agonists was accompanied by increased phosphorylation of myosin light chain 2 (MLC2) and was blocked by pretreatment of neutrophils with inhibitors of Rho-associated coiled-coil-containing protein kinase (ROCK), but not by inhibitors of the small GTPase RhoA. Taken together, these results demonstrate that mouse neutrophils express functional Tas2R126/143 and suggest a role for Tas2R126/143-ROCK-MLC2-dependent signaling in the regulation of neutrophil migration.

Micro- and Macro-Anatomical Frameworks of Lymph Nodes Indispensable for the Lymphatic System Filtering Function.

In the lymphatic vascular system, lymph nodes (LNs) play a pivotal role in filtering and removing lymph-borne substances. The filtering function of LNs involves resident macrophages tightly associated with unique lymphatic sinus structures. Moreover, an intermittently arranged LN in the lymphatic pathway is considered to cooperatively prevent lymph-borne substances from entering blood circulation. However, the functional significance of tissue microarchitecture, cellular composition, and individual LNs in the "LN chain" system is not fully understood. To explore the mechanistic and histo-anatomical significance of LNs as lymph fluid filters, we subcutaneously injected fluorescent tracers into mice and examined the details of lymphatic transport to the LNs qualitatively and quantitatively. Lymph-borne tracers were selectively accumulated in the MARCO+ subcapsular-medullary sinus border (SMB) region of the LN, in which reticular lymphatic endothelial cells and CD169+F4/80+ medullary sinus macrophages construct a dense meshwork of the physical barrier, forming the main body to capture the tracers. We also demonstrated stepwise filtration via the LN chain in the lymphatic basin, which prevented tracer leakage into the blood. Furthermore, inflammatory responses that induce the remodeling of LN tissue as well as the lymphatic pathway reinforce the overall filtering capacity of the lymphatic basin. Taken together, specialized tissue infrastructure in the LNs and their systematic orchestration constitute an integrated filtering system for lymphatic recirculation.