File:Lymph node cartoon.jpg

Schematic representation of a lymph node internal architecture

Human lymph nodes are bean-shaped structures that range in size from a few millimeters to about 1-2 cm in their normal state. Internally, two main regions can be distinguished: the medulla and the cortex. The cortex can be further divided into an inner part, the paracortex (also called the T cell area), rich in T lymphocytes and an outer area, the node cortex that includes the B cell area consisting of follicles and germinal centers, where B cells are activated and differentiate. T and B areas are identified by high concentrations of different chemokines (CCR7 and CXCR5, respectively) secreted by local stromal cells. The whole structure is supported by a dense network of fibroblastic reticular cells that encloses small lymphatic channels of 10-15 μm in diameter along which small molecules are thought to diffuse.

• T cell area - the paracortex
• B cell area the node cortex
• HEV - high endothelial venules are located inside the paracortex

A number of follicles are located in the node cortex, whereas the T cell area occupies the inner part.

The medulla consists of a part of the T-area that allows cells to exit by the efferent vessel. T and B cells enter the lymph node mainly from the blood, through HEV located inside the paracortex.

Absence of Infection

In the absence of an antigenic challenge, T and B cells randomly scan their respective areas for ~24-48 h before exiting the lymph node. Entrance of antigens into the lymph node triggers a series of events leading to antigen recognition and the activation of an immune response.

Infection

• During an infection, lymphocyte recruitment from the periphery is enhanced due to a widening of the primary arteriole feeding the lymph node.
• Once inside the lymph node, B and T cells rapidly home in their own compartments, following a specific chemotactic gradient.
• T helper cells (TH) are the fastest (average velocity of 11 μm/min)
• B cells (average velocity of 6 μm/min)
• Dendritic cells (DCs) (average velocity of 3 μm/min)

(Above text modified from original article)

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Reference

<pubmed>19939270</pubmed>| BMC Bioinformatics.

Baldazzi et al. BMC Bioinformatics 2009 10:387 doi:10.1186/1471-2105-10-387

© 2009 Baldazzi et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Original file name: 1471-2105-10-387-3.jpg