Histology: Lymph System

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Tissues and organs of the immune system

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epithelial barrier, innate immunity, adaptive immunity

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adaptive immunity

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specific response of lymphocytes to pathogens or tumors

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innate immunity

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activity of macrophages and neutrophils

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Lymphocyetes: B

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B (bone marrow derived) secrete antibodies can differenitate to become plasma cells

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Lymphocytes: T

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Thymmus derived, help regulate CD4+, cytotoxic CD8+

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Dedritic cells

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process and present antigen to cells

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Macrophages

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Phagocytic, activity regulated by antigen stimulated lymphocytes

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Secondary / Peripheral lymphatic tissue

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immune responses. Diffuse, lymph node, spleen

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Diffuse secondary tissue

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non-keratinized epithelial surfaces with little CT capsule, lymphocytes accum in CT, variability in cellularity and organization. Examples, strat sq. ep. of vagina/esophagus, BALT (resp ep.,Bronchus Associated Lymphatic Tissue, MALT (mucosal associatedlymphatic tissue in tonsils or gut)

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lymph nodes

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encapsulated receive lymph, filters lymph borne antigens

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spleen

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responds to blood borne antigens

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Primary / central lymphatic tissue

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lymphocyte production and differentiation includes bone marrow and thymus

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nodule

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dense collection of lymphocytes

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elements of diffuse lymphatic tissue

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nodules, follicles

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follicle

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dynamic collection of B cells, reflects B cell response to antigen stimulation

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Primary Follicle response to antigen stimulation

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accumulation of B cells resulting from antigen driven B cell proliferation

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Secondary follicle response to antigen stimulation

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actively producing B cells- region with mitotic lymphocytes in center= germinal center

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Germinal center

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acculumation of B cells that are reproducing and expanding making same antibody only in secondary follicle

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Role of Lymph node

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filter of lymph, site for response to lymph borne antigen

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Efferent lymphatic

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going away from lymph node toward body

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Afferent lymphatic

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coming in and breaks into channels in lymph node

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Framework of lymph node

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Lymphatic channels (sinuses) that are studded with macrophages. Stromal (framework) cells make reticular (III) fibers

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trabeculae

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dense CT for support

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Cortex of lymph node

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rich in b cells

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paracortex of lymph node

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rich in T cells and dendritic cells, site of first entry into node

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medulla

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mix of B cells, plasma cells and macrophages, T cells

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lymphocyte traffic into lymph node

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enter via blood high endothelial venules and via afferent lymph from tisse or through afferent lymphatic

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What makes post cap venuoles in lymph special?

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the enothelium is high almost cuboidal or columnar

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lymphocyte traffic thru lymph node

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enter lymph node via blood (HEV) and afferent lymph from tissues. Lymph leaves via efferent lymphatics. Lymph drains back into venous blood (thoracic duct)

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lymph recirculation purpose and description

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immune surveillance. if antigen encountered they proliferate and differentiate. If not encounter, continue to recirc for max surveillance.

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functions of spleen

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immune response to blood borne antigens, RBC filtration and removal.

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Spleen compartments

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red and white pulp

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red pulp

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site of blood filtration, system of venous sinuses, no lymph vessels, no lymphatic sinuses

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White pulp

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aggregates of lymphocytes, site of immune response to blood borne antigens

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framework cells of spleen

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mesenchymal stromal cells make reticular fibers (III)

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Spleen organization

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big vessel going into spleen called trabecular arteries/veins, tributaries go into

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Where does white pulp set itself up?

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Around central artery in spleen

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Structure of red pulp

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repeating cords of reticular CT separating venous sinuses, cords with formed elements of blood and macrophages,

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removal of sensecent ery. from circ

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Structure of the vascular sinus
facilitates removal of senescent erythrocytes from the circulation within the splenic red pulp.

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Junction type in sinus of lymph

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spot junctions (macula inherens)

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Ratio of T to B cells in spleen

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30:70

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follicle location lymph node, follicle location spleen

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outer edge, more interior

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Thymus

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site of T cell development. has epi framework (stromal cell), has cortex and medulla

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Differentiation of CLP

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occurs with least mature outside, most mature in center

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cortex of thymus

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high density of lymphocytes responsible for darker staining

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thymus medulla

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low density of lymphocytes, and lots of epi cells responsible for lighter staining

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hassalis body

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purpose? in medulla, looks like whirl

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origin of thymic epithelial stromal cells

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from 3rd Pharyngeal pouch (endoderm), some from neural crest, pharyngeal ectoderm contribution optional

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factors in thymic maturation of T cells

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needs constant supply of progenitor cells from marrow, maturation of T cells begins before birth and into sexual maturity, production of thymocytes is sensitive to irradiation and/or chemotherapeutic agents, many T cells made but few are chosen.

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Self reactive thymocytes

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autoimmune disease can occur when there is a failure to eliminate self reactive thymocytes

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Aire

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transcription factor regulating activity of self antigens in developing T cells