Afferent Lymph Research Articles

Prophylactic Buried Dermal Flap: A Simple Method for Axillary Reconstruction after Lymph Node Dissection.

Breast cancer-related lymphedema is characterized by progressive limb enlargement and occurs in up to 30% of breast cancer patients following axillary lymph node dissection (ALND). Immediate lymphatic reconstruction (ILR) is a preventative technique used to reduce lymphedema rates by performing lymphovenous anastomoses of disrupted afferent lymphatics. This study presents a novel method of axillary reconstruction following ALND using a buried dermal flap that provides local tissue with intact subdermal lymphatics to the axillary dead space. A single-center retrospective review was performed to assess breast cancer patients who underwent modified radical mastectomy without reconstruction between 2018 and 2023. Groups were divided into those who had ILR alone (group 1) and those who had buried dermal flap with attempted ILR (group 2). There were 31 patients included in this study: 18 patients in group 1 and 13 patients in group 2. Patient demographics, comorbidities, and breast cancer history were similar between the groups. There was no significant difference in the mean number of lymphovenous anastomoses performed (1.6 versus 1.7, P = 0.84). Mean operative time of 224.4 ± 51.9 minutes in group 1 was similar to 223.4 ± 30.4 minutes in group 2 (P = 0.95). We introduce a novel method of axillary reconstruction following ALND using a buried dermal flap that is inset into the axillary dissection space and over the area of ILR. We propose that it is an efficient accessory procedure to augment ILR by providing supplementary intact lymphatic channels to the area of lymphatic injury, while obliterating the axillary dead space.

Spatial Characterization of the Immune Microenvironment within HIV+ Lymph Nodes

Abstract Background: Persistent HIV replication is hypothesized to induce chronic inflammation in ART-suppressed people living with HIV (PLWH), however defining this chronic inflammation within tissues is limited. Molecular and spatial characterization of chronic inflammation within human lymph nodes from PLWH provide valuable information on the immunological microenvironment that limits viral eradication. Methods: We spatially characterized the transcriptomic and proteomic profiles of the lymph node microenvironment from 6 human lymph nodes: three from ART-suppressed PLWH, two from chronically infected PLWH, and one from a male HIV- control donor. For spatial transcriptomics analysis, lymph nodes were either from fresh-frozen or FFPE tissue. Lymph node sections (10μm) were placed onto the 10X Visium slides, stained with H&E, and imaged prior to RNA-Seq library prep. Following sequencing cluster identification was done with single cell RNA-seq datasets and downstream bioinformatics analyses were performed. Results: Following the bioinformatic integration of spatial transcriptomic datasets, cluster analysis identified pro-inflammatory T cells within the HIV+ tissues compared to the HIV- tissue within the T cell zone. Additionally, two sets of proinflammatory myeloid cells were identified that were spatially located within the afferent and efferent lymphatics in the HIV+ tissues. These proinflammatory clusters further characterize chronic inflammation that occurs in PLWH.

Role of the Afferent Lymph as an Immunological Conduit to Analyze Tissue Antigenic and Inflammatory Load

Role of the Afferent Lymph as an Immunological Conduit to Analyze Tissue Antigenic and Inflammatory Load

Dendritic Cell-Based Immunotherapy: The Importance of Dendritic Cell Migration.

Dendritic cells (DCs) are specialized antigen-presenting cells that are crucial for maintaining self-tolerance, initiating immune responses against pathogens, and patrolling body compartments. Despite promising aspects, DC-based immunotherapy faces challenges that include limited availability, immune escape in tumors, immunosuppression in the tumor microenvironment, and the need for effective combination therapies. A further limitation in DC-based immunotherapy is the low population of migratory DC (around 5%-10%) that migrate to lymph nodes (LNs) through afferent lymphatics depending on the LN draining site. By increasing the population of migratory DCs, DC-based immunotherapy could enhance immunotherapeutic effects on target diseases. This paper reviews the importance of DC migration and current research progress in the context of DC-based immunotherapy.

Tumor-driven stromal reprogramming in the pre-metastatic lymph node

Background Metastatic dissemination is critically reliant on the formation of a receptive niche, a process which is thought to rely on signals derived from the primary tumor. Lymph nodes are continuously exposed to such signals through the flow of afferent lymph, allowing the potential reprograming of lymphoid tissue stroma in support of metastases or immunosuppression. The objective of this study was therefore to better characterize tumor-driven transcriptomic changes occurring to specific stromal populations within the tumor-draining lymph node. Methods We utilize single cell RNA sequencing of dissociated LN tissue extracted from tumor-bearing and naïve mice to profile the reprograming of tissue stroma within the pre-metastatic lymph node. Results Resulting data provides transcriptomic evidence of tumor-induced imprinting on marginal reticular cells (MRCs) and floor lymphatic endothelial cells (fLECs) populating the subcapsular sinus. These alterations appear to be unique to the tumor-draining LN and are not observed during inflammatory antigenic challenge. Notably, MRCs exhibit characteristics reminiscent of early desmoplastic CAF differentiation, fLECs engage distinct chemoattractant pathways thought to facilitate recruitment of circulating cancer cells, and both stromal populations exhibit signs of metabolic reprograming and immune-modulating potential. Conclusions Cumulatively, these findings build upon existing literature describing pre-metastatic niche formation and offer several promising avenues for future exploration.

VEGF-C prophylaxis favors lymphatic drainage and modulates neuroinflammation in a stroke model.

Meningeal lymphatic vessels (MLVs) promote tissue clearance and immune surveillance in the central nervous system (CNS). Vascular endothelial growth factor-C (VEGF-C) regulates MLV development and maintenance and has therapeutic potential for treating neurological disorders. Herein, we investigated the effects of VEGF-C overexpression on brain fluid drainage and ischemic stroke outcomes in mice. Intracerebrospinal administration of an adeno-associated virus expressing mouse full-length VEGF-C (AAV-mVEGF-C) increased CSF drainage to the deep cervical lymph nodes (dCLNs) by enhancing lymphatic growth and upregulated neuroprotective signaling pathways identified by single nuclei RNA sequencing of brain cells. In a mouse model of ischemic stroke, AAV-mVEGF-C pretreatment reduced stroke injury and ameliorated motor performances in the subacute stage, associated with mitigated microglia-mediated inflammation and increased BDNF signaling in brain cells. Neuroprotective effects of VEGF-C were lost upon cauterization of the dCLN afferent lymphatics and not mimicked by acute post-stroke VEGF-C injection. We conclude that VEGF-C prophylaxis promotes multiple vascular, immune, and neural responses that culminate in a protection against neurological damage in acute ischemic stroke.

Supermicrosurgery lymphaticovenous and lymphaticolymphatic anastomosis: Technical detail and short-term follow-up for immediate lymphatic reconstruction in breast cancer treatment-related lymphedema prevention

ObjectiveWe describe the feasibility and short-term outcome of our surgical technique to repair the lymph vessel disruption directly after axillary lymph node dissection during breast cancer surgery. This procedure is called immediate lymphatic reconstruction to prevent breast cancer treatment-related lymphedema (BCRL), which frequently occurs after axillary lymph node dissection. The surgical technique consisted of lymphaticovenous anastomosis (LVA) or lymphaticolymphatic anastomosis. We named the procedure lymphatic bypass supermicrosurgery (LBS). MethodsThis study used a retrospective cohort design of patients with breast cancer between May 2020 and February 2023. LBS was performed by making an intima-to-intima coaptation between afferent lymph vessels and the recipient's veins (LVA) or efferent lymph vessels lymphaticolymphatic anastomosis. ResultsA total of 82 patients underwent lymphatic bypass. The mean age of patients was 50 ± 12 years, and most had stage III breast cancer (n = 59 [72%]). LVA was the most common type of lymphatic bypass (94.6%). The median number of LVA was 1 (range, 1-4) and 1 (range, 1-3) for lymphaticolymphatic anastomosis. The median follow-up time was 12.5 months (range, 1-33 months). The 50 patients who had postoperative indocyanine green lymphography described arm dermal backflow stage 0 in 20 (40%), stage 1 in 19 (38%), stage 2 in 2 (4%), and stage 3 in 9 (18%) cases. The proportion of BCRL was 11 (22%), and subclinical lymphedema was 19 (38%) in this period. Most cases were in stable subclinical lymphedema (10, 58.8%). The 1-year and 2-year BCRL rates were 14% (95% confidence interval, 4%-23.9%) and 22% (95% confidence interval, 10.1%-33.9%), respectively. ConclusionsAlong with the emerging immediate lymphatic reconstruction, LBS is a feasible supermicrosurgery technique that may have a potential role in BCRL prevention. A randomized controlled study would confirm the effectiveness of the technique.

Focused ultrasound ablation of melanoma with boiling histotripsy yields abscopal tumor control and antigen-dependent dendritic cell activation.

Background: Boiling histotripsy (BH), a mechanical focused ultrasound ablation strategy, can elicit intriguing signatures of anti-tumor immunity. However, the influence of BH on dendritic cell function is unknown, compromising our ability to optimally combine BH with immunotherapies to control metastatic disease. Methods: BH was applied using a sparse scan (1 mm spacing between sonications) protocol to B16F10-ZsGreen melanoma in bilateral and unilateral settings. Ipsilateral and contralateral tumor growth was measured. Flow cytometry was used to track ZsGreen antigen and assess how BH drives dendritic cell behavior. Results: BH monotherapy elicited ipsilateral and abscopal tumor control in this highly aggressive model. Tumor antigen presence in immune cells in the tumor-draining lymph nodes (TDLNs) was ~3-fold greater at 24h after BH, but this abated by 96h. B cells, macrophages, monocytes, granulocytes, and both conventional dendritic cell subsets (i.e. cDC1s and cDC2s) acquired markedly more antigen with BH. BH drove activation of both cDC subsets, with activation being dependent upon tumor antigen acquisition. Our data also suggest that BH-liberated tumor antigen is complexed with damage-associated molecular patterns (DAMPs) and that cDCs do not traffic to the TDLN with antigen. Rather, they acquire antigen as it flows through afferent lymph vessels into the TDLN. Conclusion: When applied with a sparse scan protocol, BH monotherapy elicits abscopal melanoma control and shapes dendritic cell function through several previously unappreciated mechanisms. These results offer new insight into how to best combine BH with immunotherapies for the treatment of metastatic melanoma.

Mechanisms and characteristics of subcapsular sinus macrophages in tumor immunity: a narrative review.

Lymph nodes constitute an integral component of the secondary lymphoid organs, housing a diverse population of macrophages. Macrophages exhibit heterogeneity in terms of localization, phenotype and ontogeny. Recent evidence has established that subcapsular sinus macrophages (SCSMs) are the initial cells exposed to antigens from afferent lymph vessels, playing a crucial role in the host immune response against invading pathogens and tumor cells. In order to summarize the role and mechanisms of SCSM in tumor immunity, this study systematically reviews research on SCSMs in tumor immunity. A systematic search was conducted in PubMed and Web of Science to identify articles investigating clinical significance and mechanisms of SCSMs. Study eligibility was independently evaluated by two authors based on the assessment of titles, abstracts and full-texts. The narrative review included a total of 17 studies. Previous research consistently showed that a high level of SCSM in patients with various carcinomas is associated with a favorable long-term prognosis. SCSM acts as the front-line defender in antitumor activity, engaging in intricate communication with other immune cells. Moreover, SCSM could directly and indirectly modulate tumor immunity, and the integrity of SCSM layer is interrupted in disease status. Several studies explored the feasibility of targeting SCSM to activate immunity against tumors. However, the direct molecular interactions and alternation in signal pathway in the tumor immunity of SCSM are less well established in previous researches. This narrative review underscores the critical role of SCSM in tumor immunity. Future studies should focus on the deeper mechanism underlying SCSMs and explore their clinical applications.

Bovine NK subsets in the afferent lymph and lymph nodes have distinct expression of naïve and activation-associated cell surface expressed molecules, and are differentially stimulated by BCG vaccination

Bovine natural killer (bNK) cells are heterogeneous cell populations defined by constitutive expression of the natural cytotoxicity receptor, NKp46 (CD335). Two major subsets of bNK cells, classified by differential expression of CD2, display divergent functions in innate immunity, and are hypothesised to contribute to adaptive immunity following vaccination. Here we characterised phenotypic variation of bNK cells within afferent lymph and lymph node (LN) tissues and between CD2+ and CD2- bNK subsets, and report phenotypic changes induced by BCG vaccination. CD2- bNK cells, which dominate in the afferent lymph and LN, displayed lower expression of the activation marker CD25 within the LN, with CD25+ cells being less than half as frequent as in afferent lymph. Furthermore, we found bNK cells had a lower expression of CD45RB, associated in cattle with naïve cell status, within LN compared to afferent lymph. Following BCG vaccination, bNK cells in afferent lymph draining the vaccination site showed increased CD2-CD25+ frequencies and increased expression of CD25 on CD2+ bNK cells, although the frequency of these cells remained unchanged. In summary, we provide an overview of the phenotype of bNK cells within bovine lymphatic tissues, and provide an indication of how subsets may diverge following BCG vaccination.

A CCL5 chemokine trail laid down by migratory dendritic cells directs CCR5 +antigen-presenting monocytes into draining lymph nodes

Abstract Antigen presenting dendritic cells (DCs) and monocytes capture and transport antigens from barrier tissues for presentation to antigen-specific T cells in the draining-lymph nodes (LNs). While DCs enter LNs through afferent lymphatics in a CCR7-dependent manner, how exactly antigen-carrying monocytes reach LNs is less clear since monocytes do not express CCR7 and can also enter LNs via the bloodstream. In steady state, and following injection of several PAMPs, scRNA-seq data on LN mononuclear phagocytes identified LN resident versus migratory type 1 and type 2 conventional (c)DCs despite downregulation of DC subset-defining transcripts, such as Xcr1, Clec9a, H2-Ab1, Sirpa, and Clec10a on migratory cDCs. Migratory cDCs gained expression of transcripts controlling cellular migration such as Ccr7, Ccl17, Ccl22, and Ccl5, while migratory monocytes expressed Ccr5 without Ccr7. Using two tracking methods and a gating strategy that clearly distinguishes migratory CD88 hiCD26 lomonocytes from CD88 −CD26 hicDCs, we found that both captured antigens in the lung and migrated to lung draining LNs. Using global and mixed-chimeric Ccl5-, Ccr2-, Ccr5-, Ccr7-, and Batf3-deficient mice, we found that CCR5 +monocytes follow CCL5-secreting migratory cDCs to reach the draining LN via lymphatic vessels. In a model of asthma, such recruited monocytes regulated the induction of type 2 immunity. Overall, our data suggest that CCL5-secreting migratory cDCs lay down the chemokine trail for CCR5+ antigenpresenting monocytes to reach draining lymph nodes and regulate adaptive immunity. This work was supported by National Institutes of Health grants R01 HL115334, R01 HL135001, and R35 HL155458 (CVJ)

Cutaneous Malignant Melanoma Presenting as an Isolated Splenic Metastasis: An Update.

Although the spleen is a highly vascularized organ, metastatic deposits from non-hematolymphoid solid malignancies are rare. This is reasoned to the inherent resistance of the splenic parenchyma to harbor metastases. The splenic capsule, lack of afferent lymphatics, contractile properties of the spleen, and the angular and gyroid course of the splenic artery form several barriers against the metastatic spread of malignant tumors. Moreover, the immune cells in the white and red pulps of the spleen have strong defensive ability against the tumor cells. Metastasis from solid tumors to the spleen often occurs only during widespread distant spread. Malignant melanoma is a rare but fatal malignancy. Isolated splenic metastasis from malignant melanoma is exceptionally rare. Studies that addressed the splenic metastasis from cutaneous malignant melanoma are scarce. This minireview was performed to address this subject. Here we present an overview of the clinicopathologic features of isolated splenic metastatic melanoma. The diagnostic biochemical markers in melanoma are also discussed.

Lymphatic Tissue Transfer: Ultrasound-Guided Description and Preoperative Planning of Vascularised Lymph Nodes, Lymphatic Units, and Lymphatic Vessels Transfers.

Background: The modern concept of lymphatic transfer includes vascularised lymph node transfer (VLNT), lymphatic vessels transfer (lymph interpositional flap transfer, LIFT) and lymphatic system transfer (vascularised lymph nodes and afferent lymphatics, LYST). The aim of this paper was to report our experience with different types of lymphatic transfer. Patients and Method: From June 2016 to June 2020, 30 consecutive patients affected by extremity lymphedema and 15 patients affected by post-traumatic lower extremity soft tissue defects, underwent lymphatic transfer (VLNT, LYST or LIFT). All cases were preoperatively evaluated by both high frequency and ultra-high frequency ultrasound. Flap features were recorded, as well as qualitative and quantitative outcomes at 1 year postoperative. Results: The mean postoperative lymphedema index reduction was 7.2 ± 5.7 for upper extremity and 20.7 ± 7.1 for lower extremity. No dismission of compression garments occurred, 12 patients (26%) referred more stable results of physical treatment and 1 case showed a 1-class compression reduction. All the LIFTs aimed as preventive did not develop post-traumatic lymphedema. In all cases of distal placement of VLNT and/or LYST, patients were dissatisfied with the aesthetic appearance of reconstruction, while no donor site scar disappointment was referred. Conclusion: When LVA is not feasible, LTT may represent a valid treatment option. This report was aimed at comprehensively describing and assessing how different lymphatic tissue transfer modalities may fulfil the different reconstructive needs of lymphedema patients.

Lymphatic endothelial sphingosine 1-phosphate receptor 1 enhances macrophage clearance via lymphatic system following myocardial infarction.

Lymphatic endothelial cell homeostasis plays important roles in normal physiological cardiac functions, and its dysfunction significantly influences pathological cardiac remodeling after myocardial infarction (MI). Our results revealed that sphingosine 1-phosphate receptor 1 (S1pr1) expression in cardiac lymphatic endothelial cells (LECs) was sharply changed after MI. It has been shown that S1pr1 tightly controlled LEC functions and homeostasis. We thus hypothesized that lymphatic endothelial S1pr1 might be involved in post-MI cardiac remodeling. We generated LEC-conditional S1pr1 transgenic mice, in which S1pr1 expression was reduced in cardiac LECs. We performed the left anterior descending coronary artery (LAD) ligation operation to induce MI in these mice. Cardiac functions and remodeling were examined by echocardiography analysis and serial histological analysis. Meanwhile, we performed adoptive cell transfer experiments to monitor macrophage trafficking in post-MI myocardium and their draining lymphatic system. Furthermore, in vitro cell culture experiments and mechanism studies were undertaken to uncover the molecular mechanism by which LEC-S1pr1 regulated cardiac inflammation and remodeling after MI. Our results showed that S1pr1 expression significantly decreased in cardiac LECs after MI. Our in vivo experiments showed that the reduced expression of LEC-S1pr1 deteriorated cardiac function and worsened pathological cardiac remodeling after MI. Our further results demonstrated that the reduced expression of LEC-S1pr1 did not influence macrophage infiltration in an early inflammatory phase of MI, but significantly affected macrophages clearance in the later phase of MI via afferent cardiac lymphatics, and thus influenced inflammatory responses and cardiac outcome after MI. Further study showed that S1P/S1pr1 activated ERK signaling pathway and enhanced CCL2 expression, which promoted macrophage trafficking in a paracrine manner. This study reveals that cardiac lymphatic endothelial cells tightly control macrophage trafficking via lymphatic vessels in injured hearts via S1P/S1pr1/ERK/CCL2 pathway and thus regulate post-MI immune modulation and heart repair. This study highlights the importance of cardiac lymphatic vessel system in orchestrating post-MI immune responses and cardiac remodeling by regulating macrophage transit in injured hearts. Our finding implies that a feasible modulation of S1pr1 signaling in LECs might provide a promising target to resolve excessive inflammation and to ameliorate adverse cardiac remodeling after MI.

The Internal Conduit System of the Swine Inverted Lymph Node.

Lymph nodes (LN) are the crossroad where naïve lymphocytes, peripheral antigens and antigen presenting cells contact together in order to mount an adaptive immune response. For this purpose, LN are highly organized convergent hubs of blood and lymphatic vessels that, in the case of B lymphocytes, lead to the B cell follicles. Herein take place the selection and maturation of B cell clones producing high affinity antibodies directed against various antigens. Whereas the knowledge on the murine and human LN distribution systems have reached an exquisite precision those last years, the organization of the antigens and cells circulation into the inverted porcine LN remains poorly described. Using up to date microscopy tools, we described the complex interconnections between afferent lymphatics and blood vessels, perifollicular macrophages, follicular B cells and efferent blood vessels. We observed that afferent lymphatic sinuses presented an asymmetric Lyve-1 expression similar to the one observed in murine LN, whereas specialized perifollicular sinuses connect the main afferent lymphatic sinus to the B cell follicles. Finally, whereas it was long though that mature B cells egress from the inverted LN in the T cell zone through HEV, our observations are in agreement with mature B cells accessing the efferent blood circulation in the efferent, subcapsular area. This understanding of the inverted porcine LN circuitry will allow a more accurate exploration of swine pathogens interactions with the immune cells inside the LN structures. Moreover, the mix between similarities and differences of porcine inverted LN circuitry with mouse and human normal LN shall enable to better apprehend the functions and malfunctions of normal LN from a new perspective.

Lymphatic flow through (LyFT) ALT flap: an original solution to reconstruct soft tissue loss with lymphatic leakage or lower limb lymphedema

Introduction The lympho-venous shunt using the distal vein of ALT flap pedicle allowed at the same time the coverage of the inguinal defects and to perform lymphovenous shunt into a run-in vein of the descending branch of the lateral circumflex femoral pedicle, draining the lymph through the flap pedicle. Surgical technique, complications and final outcomes (both clinical and lymphoscintigraphic) are reported. Methods Five patients (45.8 y.o.[22–70]) with groin soft tissue loss with lymphatic leakage or lower limb lymphedema, benefited of the described technique. The ALT flap was used to cover the defect and, at the same time, we could perform a lymphovenous shunt between afferent lymphatics to the thigh and the descending branch of the lateral circumflex femoral pedicle, distal to the perforator nourishing the flap. Clinical and lymphoscintigraphic assessment of the limbs, cease of lymphorrhea or cellulitis/lymphangitis episodes, eventual downstaging of physiologic/physical therapy were recorded. LYMphatic Quality Of Life in leg (LYMQoLLeg) and patient satisfaction were evaluated. Results Average flap size was 88.8cm2 (range 84–126). The mean number of multi-lymphovenous anastomosis (MLVA) performed was 1.8 (range 1–3) per patient with 1–3 lymphatics shunted into each vein. Only one hemato-seroma requiring surgical revision. Mean improvement of perometer values was 48.2% (range 27.7–67.7) with an average follow-up of 13.6 months (range 12–17). Lymphoscintigraphy showed disappearing of the lymphatic leak and lymphedema with a high satisfaction of LYMQoL score. Discussion The combination of pedicle flap with lympho-venous bypass as lymphatic derivation concept, improving the chronic morbidity scenarios of lymphatic complications.

Mechanosensitive ACKR4 scavenges CCR7 chemokines to facilitate Tcell de-adhesion and passive transport by flow in inflamed afferent lymphatics.

T cell migration via afferent lymphatics to draining lymph nodes (dLNs) depends on expression of CCR7 in Tcells and CCL21 in the lymphatic vasculature. Once Tcells have entered lymphatic capillaries, they slowly migrate into contracting collecting vessels. Here, lymph flow picks up, inducing Tcell detachment and rapid transport to the dLNs. We find that the atypical chemokine receptor 4 (ACKR4), which binds and internalizes CCL19 and CCL21, is induced by lymph flow in endothelial cells lining lymphatic collectors, enabling them to scavenge these chemokines. In the absence of ACKR4, migration of Tcells to dLNs in TPA-induced inflammation is significantly reduced. While entry into capillaries is not impaired, Tcells accumulate in the ACKR4-deficient dermal collecting vessel segments. Overall, our findings identify an ACKR4-mediated mechanism by which lymphatic collectors facilitate the detachment of lymph-borne Tcells in inflammation and their transition from crawling to free-flow toward the dLNs.

Extracellular ATP Limits Homeostatic T Cell Migration Within Lymph Nodes.

Whereas adenosine 5’-triphosphate (ATP) is the major energy source in cells, extracellular ATP (eATP) released from activated/damaged cells is widely thought to represent a potent damage-associated molecular pattern that promotes inflammatory responses. Here, we provide suggestive evidence that eATP is constitutively produced in the uninflamed lymph node (LN) paracortex by naïve T cells responding to C-C chemokine receptor type 7 (CCR7) ligand chemokines. Consistently, eATP was markedly reduced in naïve T cell-depleted LNs, including those of nude mice, CCR7-deficient mice, and mice subjected to the interruption of the afferent lymphatics in local LNs. Stimulation with a CCR7 ligand chemokine, CCL19, induced ATP release from LN cells, which inhibited CCR7-dependent lymphocyte migration in vitro by a mechanism dependent on the purinoreceptor P2X7 (P2X7R), and P2X7R inhibition enhanced T cell retention in LNs in vivo. These results collectively indicate that paracortical eATP is produced by naïve T cells in response to constitutively expressed chemokines, and that eATP negatively regulates CCR7-mediated lymphocyte migration within LNs via a specific subtype of ATP receptor, demonstrating its fine-tuning role in homeostatic cell migration within LNs.

Mathematical Modeling of Lymph Node Drainage Function by Neural Network

The lymph node (LN) represents a key structural component of the lymphatic system network responsible for the fluid balance in tissues and the immune system functioning. Playing an important role in providing the immune defense of the host organism, LNs can also contribute to the progression of pathological processes, e.g., the spreading of cancer cells. To gain a deeper understanding of the transport function of LNs, experimental approaches are used. Mathematical modeling of the fluid transport through the LN represents a complementary tool for studying the LN functioning under broadly varying physiological conditions. We developed an artificial neural network (NN) model to describe the lymph node drainage function. The NN model predicts the flow characteristics through the LN, including the exchange with the blood vascular systems in relation to the boundary and lymphodynamic conditions, such as the afferent lymph flow, Darcy’s law constants and Starling’s equation parameters. The model is formulated as a feedforward NN with one hidden layer. The NN complements the computational physics-based model of a stationary fluid flow through the LN and the fluid transport across the blood vessel system of the LN. The physical model is specified as a system of boundary integral equations (IEs) equivalent to the original partial differential equations (PDEs; Darcy’s Law and Starling’s equation) formulations. The IE model has been used to generate the training dataset for identifying the NN model architecture and parameters. The computation of the output LN drainage function characteristics (the fluid flow parameters and the exchange with blood) with the trained NN model required about 1000-fold less central processing unit (CPU) time than computationally tracing the flow characteristics of interest with the physics-based IE model. The use of the presented computational models will allow for a more realistic description and prediction of the immune cell circulation, cytokine distribution and drug pharmacokinetics in humans under various health and disease states as well as assisting in the development of artificial LN-on-a-chip technologies.

Characterisation of dendritic cell frequency and phenotype in bovine afferent lymph reveals kinetic changes in costimulatory molecule expression

The bovine afferent lymphatic cannulation model allows collection of large volumes of afferent lymph and provides an opportunity to study lymphatic cells trafficking from the periphery directly ex-vivo. The technique requires surgical intervention, but influence of the procedure or time post-surgery on cells trafficking in the lymph has not been well documented. Here, we measured the volume of lymph and number of cells/mL collected daily over a two week time-course. Animal to animal variability was demonstrated but no consistent changes in lymph volume or cell density were observed in relation to time post-cannulation. Cell populations (dendritic cells, αβ T-cells, γδ T-cells and NK cells) were analysed by flow cytometry at 1, 3 and 10 days post-cannulation (DPC) and a reduced percentage of γδ T-cells in afferent lymph was observed at 1 DPC. In addition, cell surface molecule expression by afferent lymphatic dendritic cells (ALDC) was assessed due to the key role of these cells in initiating an adaptive immune response. Co-stimulatory molecules CD80 and CD86 were upregulated by CD172a+ve ALDC early in the time-course, suggesting that the cannulation procedure and duration of experiment may impact the activation state of DCs in the naïve host. This should be considered when analysing the response of these cells to vaccines or pathogens.