Blood–thymus barrier

The blood–thymus barrier regulates exchange of substances between the circulatory system and thymus, providing a sequestered environment for immature T cells to develop. The barrier also prevents the immature T cells from contacting foreign antigens (since contact with antigens at this stage will cause the T cells to die by apoptosis).

The barrier is formed by the continuous blood capillaries in the thymic cortex, reinforced by epithelial reticular cells and macrophages.

Spleen	structural: Hilum Trabeculae Diaphragmatic surface of spleen Visceral surface of spleen Red pulp Cords of Billroth Marginal zone White pulp Periarteriolar lymphoid sheaths Germinal center blood flow: Trabecular arteries Trabecular veins

Tonsils	Palatine Lingual Pharyngeal Tubal Tonsillar crypts Waldeyer's tonsillar ring

Lymph nodes	lymph flow: Afferent lymph vessels Cortical sinuses Medullary sinuses Efferent lymph vessels T cells: High endothelial venules B cells: Primary follicle/Germinal center Mantle zone Marginal zone layers: Capsule/Trabeculae Subcapsular sinus Cortex Paracortex Medulla (Medullary cord) Hilum

MALT	GALT Peyer's patch Germinal center

T cells	αβ (Cytotoxic CD8⁺ Helper CD4⁺ / T_FH / T_h3 / T_h17 / Regulatory) γδ Naïve Natural killer T cell

NK cells

Lymphopoiesis

Immunology: lymphocytic adaptive immune system and complement

Lymphoid

Antigens	Antigen Superantigen Allergen Hapten Epitope Linear Conformational Mimotope Antigen presentation/Professional APCs: Dendritic cell Macrophage B cell Immunogen

Antibodies	Antibody Monoclonal antibodies Polyclonal antibodies Autoantibody Microantibody Polyclonal B cell response Allotype Isotype Idiotype Immune complex Paratope

Immunity vs. tolerance	action: Immunity Autoimmunity Alloimmunity Allergy Hypersensitivity Inflammation Cross-reactivity inaction: Tolerance Central Peripheral Clonal anergy Clonal deletion Tolerance in pregnancy Immunodeficiency

Immunogenetics	Affinity maturation (Somatic hypermutation Clonal selection) V(D)J recombination Junctional diversity Immunoglobulin class switching MHC/HLA

Lymphocytes

Substances

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Blood–thymus barrier

See also