Mouse Lymph Node Map: Insights Into Node Organization

Mapping the lymph nodes of mice provides valuable insights into their structure and function. These small but critical organs serve as hubs for immune responses, filtering pathogens and coordinating immune cell activity. Understanding their architecture helps researchers study disease progression, immune interactions, and potential therapeutic targets.

Advancements in imaging and molecular techniques have allowed for a more detailed examination of lymph node organization. This research enhances our ability to model human immune processes using mice, with implications for immunology and medical science.

Lymph Node Compartment Organization

Mouse lymph nodes are composed of distinct compartments, each serving specialized functions. These include the cortex, paracortex, medulla, and subcapsular sinus, each defined by unique stromal networks and extracellular matrix components.

The cortex, located at the periphery, contains lymphoid follicles primarily composed of B cells. These follicles are classified into primary follicles, which contain naïve B cells, and secondary follicles, which develop germinal centers in response to antigenic stimulation. Follicular dendritic cells (FDCs) provide structural support and present antigens to B cells, promoting affinity maturation and selection.

Beneath the cortex, the paracortex is rich in T cells and dendritic cells, where antigen presentation and T cell activation occur. Fibroblastic reticular cells (FRCs) form a conduit system that regulates the movement of small molecules and chemokines. FRCs produce CCL19 and CCL21, which guide T cells and dendritic cells via CCR7 signaling. This spatial arrangement ensures efficient encounters between antigen-presenting cells and naïve T cells. The paracortex also contains high endothelial venules (HEVs), specialized blood vessels lined with cuboidal endothelial cells that express adhesion molecules like PNAd and ICAM-1. These structures enable lymphocyte recruitment from the bloodstream, regulated by L-selectin and chemokine gradients.

The medulla consists of medullary cords and sinuses, which serve as conduits for lymphatic drainage and cellular trafficking. Medullary cords contain plasma cells, macrophages, and reticular fibers, contributing to lymph filtration and debris removal. Medullary sinuses, lined by lymphatic endothelial cells, facilitate the exit of lymphocytes and antigen-presenting cells into efferent lymphatic vessels. This compartmentalized structure ensures efficient immune cell distribution and proper lymph filtration before re-entering circulation.

Blood Vascular Patterns

The blood vasculature of mouse lymph nodes is specialized to support nutrient delivery and cellular trafficking. A dense capillary network permeates the cortex, ensuring proliferating lymphocytes receive adequate oxygen and nutrients. These capillaries transition into postcapillary venules, which are uniquely adapted to mediate lymphocyte entry. HEVs, lined with cuboidal endothelial cells, express adhesion molecules and chemokines that facilitate lymphocyte extravasation.

Arterial branches penetrate the node through the hilum before branching into smaller arterioles that supply the cortex and paracortex. These arterioles form an intricate capillary plexus that delivers oxygenated blood to lymphoid follicles and surrounding stromal cells. Endothelial cells lining these vessels exhibit regional heterogeneity, reflecting their functional roles. For example, capillaries in B cell follicles have distinct expression profiles compared to those in T cell zones, suggesting localized regulatory mechanisms for vascular permeability and cell migration.

Venous drainage begins at the medullary sinuses, where deoxygenated blood collects before exiting through larger venous conduits. The medullary vasculature plays a role in fluid homeostasis and waste removal. The transition from high-resistance arterioles to low-resistance venules ensures steady blood flow, preventing hypoxia in metabolically active regions. Intravital microscopy studies have shown that blood velocity varies across compartments, with slower flow rates in the paracortex optimizing lymphocyte-endothelial interactions.

Lymphatic Vessels in the Node

Lymphatic vessels in mouse lymph nodes regulate fluid transport and cellular migration. These vessels are classified as afferent and efferent lymphatics, each with distinct roles in tissue homeostasis. Afferent lymphatics, originating from peripheral tissues, deliver lymph containing soluble molecules and cells to the subcapsular sinus. This compartment is lined by lymphatic endothelial cells (LECs) that express scavenger receptors and junctional proteins, allowing selective permeability. Anchoring filaments reinforce vessel integrity, responding to interstitial pressure changes by modulating dilation and contraction.

As lymph moves inward, it traverses cortical and medullary sinuses before reaching efferent lymphatics. These passageways regulate molecular exchange and cellular interactions. The cortical sinuses form a labyrinthine structure that slows lymph flow, enhancing antigen exposure. Medullary sinuses widen into broader channels that facilitate bulk transport toward the efferent exit. Lymphatic flow is modulated by rhythmic contractions of lymphatic muscle cells, generating pressure gradients that propel lymph forward.

Efferent lymphatic vessels merge into larger collecting ducts that drain into the thoracic duct or right lymphatic duct. These vessels contain intraluminal valves that prevent backflow and ensure unidirectional movement. Molecules such as VEGF-C and PROX1 regulate efferent lymphatic maintenance and remodeling, particularly during inflammation or disease. Genetic knockout studies have shown that disruptions in these pathways impair lymphatic drainage, leading to localized edema and altered fluid balance.

Distribution of Immune Cell Subsets

The spatial distribution of immune cells within mouse lymph nodes is highly organized. B cells localize to cortical follicles, where they aggregate in clusters supported by follicular dendritic cells. These structures facilitate antigen recognition and affinity maturation, with germinal centers marking sites of active B cell proliferation. CXCR5 signaling, in response to CXCL13 gradients, guides B cell movement and retention within this niche.

T cells are concentrated in the paracortex, where they interact with antigen-presenting dendritic cells. This region is structured by a fibroblastic reticular cell network, which provides scaffolding and chemokine cues such as CCL19 and CCL21 to direct T cell trafficking. Regulatory T cells (Tregs) are interspersed among conventional CD4+ and CD8+ T cells, modulating immune responses through contact-dependent and cytokine-mediated mechanisms. The density and composition of T cell subsets fluctuate based on antigen exposure and inflammatory signals, reflecting the dynamic nature of lymph node immunity.

Molecular Markers of Node Architecture

The structural integrity and compartmentalization of mouse lymph nodes rely on molecular markers that define cellular and stromal populations. These markers delineate specific regions and regulate interactions between immune and non-immune cells.

Stromal cells, including fibroblastic reticular cells (FRCs) and lymphatic endothelial cells (LECs), express proteins that shape the extracellular matrix and influence cellular migration. FRCs produce ER-TR7, a reticular fiber-associated protein that supports the paracortex’s structural framework. Podoplanin (PDPN) maintains the conduit system that facilitates small molecule and chemokine transport. LECs express LYVE-1 and PROX1, essential for lymphatic vessel formation and function. These markers distinguish lymphatic endothelium from blood vasculature and regulate fluid dynamics within the node.

Endothelial cells within HEVs exhibit a unique molecular profile that governs lymphocyte trafficking. Peripheral node addressin (PNAd), a carbohydrate ligand for L-selectin, is highly expressed on HEVs, facilitating lymphocyte adhesion. MECA-79, a monoclonal antibody recognizing sulfated glycoproteins on HEVs, serves as a marker for identifying these venules. Chemokines such as CCL19 and CCL21 further reinforce T cell and dendritic cell recruitment to the paracortex, ensuring efficient antigen presentation. Single-cell RNA sequencing has identified additional markers, such as MAdCAM-1 and VCAM-1, which play roles in lymphocyte retention and endothelial integrity. These molecular signatures provide insights into lymph node organization and potential therapeutic targets for modulating immune responses.