Lymph nodes - not lymphoma

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Images are particularly needed for these topics: in lymph node - marginal zone, centroblasts, centrocytes, B cells, T cells, NK cells, macrophages, mast cells, dendritic cells (all types, also EM), littoral cells, CR3 deficiency, Brugia, HIV, mycobacterial spindle cell pseudotumor, parvovirus, pseudofungi, syphilis, vaccinia, Yersinia (all species), amyloid, chronic lymphadenitis, clofazimine, extramedullary hematopoiesis, hyaline deposits, Kawasaki disease, lipogranuloma, lymphedema, mantle cell/marginal zone hyperplasia, monocytoid B cell hyperplasia, Sjogren’s syndrome, vasculitis, angiolipomatous hamartomas, angiomyomatous hamartoma

Embryology of lymph node

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Develop from lateral plate mesoderm (on either side of intermediate mesoderm)

Image: animation of lateral plate mesoderm (slow loading)

First, lymphatic sacs arise from endothelial outgrowths of large central veins at week 5

Second, lymphatic plexus develops from lymphatic sacs

Third, plexuses are invaded by mesenchymal cells that proliferate and aggregate to form lymph nodes

Small collections of lymphoblasts are present by first trimester

By second trimester, cortex is distinguishable from medulla and primary follicles are present

Drawing: development of lymph node

References: Human Anatomy - Pearson

Normal anatomy/histology of lymph node

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A secondary lymphoid organ (where B and T cells proliferate in response to exogenous antigen)

Primary lymphoid organs are bone marrow and thymus

Other secondary lymphoid organs are spleen and Peyer’s patches

Tertiary lymphoid organs are tissues with few lymphocytes that recruit more when inflammation is present

Lymph nodes are organized to detect and inactivate foreign antigens present in lymph fluid that drains skin, GI tract and respiratory tract, the major organs in contact with the environment

Gross: ovoid with gray-tan cut surface

Micro: at low power, lymph node structures are capsule, cortex and medulla, follicles, paracortex, sinuses

Afferent lymph vessels: penetrate capsule, enter marginal sinus, communicate with intranodal sinuses, then become efferent vessels, which lack an endothelial lining; intranodal vessels contain littoral cells or histiocytes with phagocytic properties

Capsule: thin fibrous connective tissue covering of lymph node; may be thicker at hilus; connected to fibrous trabeculae which penetrate the node; capsule may contain smooth muscle cells (Anat Rec 1975;183:517)

Micro images: capsule and subcapsular sinus #1; #2

Cortex: subcapsular portion of node with largest number of follicles

Germinal center: contains centroblasts and centrocytes; also macrophages and follicular dendritic cells; surrounded by a mantle zone of small B lymphocytes (which resembles the primary follicle, see below)

Micro images: germinal center #1; #2; #3; #4

Positive stains: strong and dense bcl6 and CD10

Negative stains: bcl2

Mantle zone: small B cells surrounding pale staining germinal centers

Micro images: mantle zone #1; #2

Marginal zone: light zone on outer rim of mantle zone; contains post-follicular memory B cells derived after stimulation of recirculating cells from T cell dependent antigen

Medulla: portion of node closest to hilum; contains vessels and sinuses and mast cells but minimal number of follicles

Medullary cords: found in hilar region between the sinuses, composed mostly of small B and T lymphocytes

Micro images: medullary cords and sinuses

Paracortex: tissue between cortical follicles and medulla; mostly dark staining; contains post-capillary venules (lined by high endothelial cells with intraendothelial lymphocytes), dendritic cells and T cells; expands during cell-mediated immunological reactions; has coarse network of reticulin fibers

Micro images: paracortex; post-capillary venule of paracortex

Primary follicle: round aggregates of small, dark staining lymphocytes, usually near the capsule, within a network of follicular dendritic cell processes; no germinal center present

Secondary follicle: arise from primary follicles that develops germinal centers (see below) due to antigenic stimulation of B cells and production of antibodies; contains pale staining germinal center which may be polarized towards site of antigen entry; contains B cells, follicular dendritic cells (CD21+, CD35+) and tingible body macrophages

Micro images: germinal center #1; #2

Sinuses: carry lymph from afferent to efferent lymphatics; subcapsular sinus is below capsule and partially lined by endothelium; becomes “medullary” as it approaches the hilum and is lined by macrophages

Micro images: subcapsular sinus #1; #2

Vessels: blood enters and leaves lymph node at hilus

Drawings: lymph node structures #1; #2; #3; #4

Micro images: low power #1; #2; cortex and medulla #1; #2; reticular network (silver stain); various images

Normal cell population of lymph node

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