Lecture 24: Immune/Lymph 2 Flashcards
Describe the histological organization of the thymus and list major characteristics
NO lymph follicles (nodules), afferent lymph vessels, lymph sinuses
Most developed at puberty then declines from there.
Capsule contains blood vessels and efferent lymphatics, and trabeculae into parenchyma
Trabeculae divides into incomplete lobules
List source of thymosin
Epithelial reticular cells in the outer cortex
This matures T lymphocytes
Describe the role of the epithelial barrier surrounding blood vessels.
Epithelial barrier surrounding blood vessels allows thymus to maintain lymphopoiesis while segregated from antigens
Describe the role of Hassall’s corpuscles
Hassalls corpuscles are whorls of highly keratinized medullary epithelial cells.
Produce cytokine thymic stromal lymphopoietin: stimulates thymic dendritic cells needed for the maturation of single positive T cells
Describe, in detail, the changes in T cells as they move into the thymus through the subscapular space, outer cortex, inner cortex, and medulla.
Double negative T cells enter cortex from blood vessels and proliferate in subscapular area
Confrontation w/ epithelial cells w/ surface MHC classes I and II->express both CD4 and CD8 coreceptors and TCR receptors-double positive T cells move to outer cortex. (Deeper in cortex)
Lose expression of CD4 or CD8 and increase TCR expression. In medulla, these are single positive T cells
Clonal deletion occurs in medulla
Describe the role of Foxn1 and Aire genes in the differentiation of T cells.
Foxn1: essential for differentiation of thymic epithelial cells.
Aire: promotes the expression of a portfolio of tissue-specific cell proteins by thymic medullary epithelial cells, which normally do not express these proteins.
These proteins permit the identification and disposal of autoreactive T cells.
Distinguish btw keratin 5+ and keratin 18+ thymine epithelial cells
Thymic epithelial cells from cortex and medula derive from a common ectodermal cell precursor expressing keratin 5 and keratin 18
Cortical thymic epithelial cells express keratin 18. -clonal selection
Medullary thymic epithelial cells express keratin 5-clonal deletion
Describe the structure/components of the blood-thymus barrier.
In thymic cortex, it prevents antigens in the blood from reaching developing T cells in thymic cortex.
This is where T cells binding to own antigens are destroyed- conditions asso. Are autoimmune.
Inner capillary lined by continuous endothelial cells. Surrounded by endothelium basal lamina. Surrounded by thymic cortical epithelial cells and T cells, macrophages.
Describe the general histology of the spleen
No lymph sinuses or afferent lymph vessels.
Covered by peritoneum except hilus.
Mesothelioma-lined CT capsule contains some smooth muscle fibers and sends trabeculae into parenchyma.
Blood vessels enter and leave hilus.
Divided into red pulp and white pulp–characteristic of spleen
List the functions of the spleen.
Blood-filtering: only organ.
Stores and removes worn-out RBCs and recycles Fe.
Converts hemoglobin to bilirubin.
Blood formation in the fetus.
Immune:
Screens foreign material in the blood.
Produces lymphocytes and plasma cells. Removal leads to overwhelming bacterial infections in infants, children, and young adults.
Compare histology and function of the white pulp to the red pulp.
White pulp: branched strands always asso. W/ arteries. Zones of diffuse lymphoid Tissue and germinal centers. Site of clonal expansion of antigen-stimulated lymphocytes. B cell area has 2ndary follicles
Red pulp: surrounds white pulp and makes up about 80% of the spleen. Filters blood. Contains large number of RBC’s/ blood elements.
Describe the PALs; where are they located?
T cells are found in the areas surrounding the central artery near the center of the white pulp–forms the periarterial lymphatic sheath (PALS)
Found in the center of the white pulp
Describe billroth cords; where are they located?
Billroth cords: contain various blood cells, plasma cells, and antigen-presenting cells. Terminal capillaries open directly into substance of cords [open circulation]. Macrophages destroy worn-out or defective RBCs.
Billroth cords form red pulp parenchyma
Describe in detail the vascularis action of the spleen and the movement of blood cells
Splenic artery enters hilus. Trabecular arteries branch off. Central arteries. After capillaries form, supplying white pulp, central arteries lose their white pulp investment and enter red pulp to form a penicillus. Terminal capillary.
Venous sinuses are lined w/ reticuloendothelial cells
Compare open and closed systems in the vascular drainage pattern
Open system: drains into intercellular spaces
Closed system: venous sinuses w/ reticuloendothelial cells
