TY - CHAP M1 - Book, Section TI - Lymphadenopathy and Splenomegaly A1 - Jameson, J. Larry A1 - Fauci, Anthony S. A1 - Kasper, Dennis L. A1 - Hauser, Stephen L. A1 - Longo, Dan L. A1 - Loscalzo, Joseph Y1 - 2020 N1 - T2 - Harrison's Manual of Medicine, 20e AB - Exposure to antigen through a break in the skin or mucosa results in antigen being taken up by an antigen-presenting cell and carried via lymphatic channels to the nearest lymph node. Lymph channels course throughout the body except for the brain and the bones. Lymph enters the node through the afferent vessel and leaves through an efferent vessel. Because antigen-presenting cells pass through lymph nodes, they present antigen to lymphocytes residing there. Lymphocytes in a node are constantly being replaced by antigen-naïve lymphocytes from the blood. They are retained in the node via special homing receptors. B cells populate the lymphoid follicles in the cortex; T cells populate the paracortical regions. When a B cell encounters an antigen to which its surface immunoglobulin can bind, it stays in the follicle for a few days and forms a germinal center where the immunoglobulin gene is mutated in an effort to make an antibody with higher affinity for the antigen. The B cell then migrates to the medullary region, differentiates into a plasma cell, and secretes immunoglobulin into the efferent lymph. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/11/10 UR - accessmedicine.mhmedical.com/content.aspx?aid=1167063333 ER -