Lymphoid dendritic cells

Dendritic cells (DC) are important antigen-presenting cells mostly derived from the bone marrow. Microscopically they show characteristic long cytoplasmic extensions called dendrites. There are several types of specialized DC present in all lymphoid tissues and major... 

In the specialized environment of secondary lymphoid tissues such as lymph nodes or spleen, dendritic cells provide the requirements for naive T-lymphocytes to become activated and to proliferate. The professional antigen-presenting cells present peptides in MHC II, express costimulatory molecules, and release cytokines into the immunological synapse, which is formed by the antigen-presenting cell and the naive T-lymphocyte. Thus, cells of innate immunity initiate and facilitate the activation of naive lymphocytes, and it is easily conceivable that their cytokines and adhesion molecules will instruct the naive T-lymphocyte during activation and differentiation to T-effector cells. 

Yoneyama H, Matsuno K, Zhang Y, et al. Regulation by chemokines of circulating dendritic cell precursors, and the formation of portal tract-associated lymphoid tissue, in a granulomatous liver disease. J Exp Med 2(X)I I93(I) 35M9. 

Ngo VN, Tang HL, Cyster JG. Epstein-Barr virus-induced molecule 1 ligand chemokine is expressed by dendritic cells in lymphoid tissues and strongly attracts naive T cells and activated B cells. J Exp Med 1998 188(1) 181—191. 

Page G, Lebecque S, Miossec P. Anatomic localization of immature and mature dendritic cells in an ectopic lymphoid organ correlation with selective chemokine expression in rheumatoid synovium. J Immunol 2002 168(10) 5333-5341. 

There are at least three potential reservoirs. The first phase reflects virus produced predominantly from activated CD4+ T cells. Extracellular virus particles can be trapped on specialized cells in the germinal centers of the peripheral lymphoid tissues. These cells, known as follicular dendritic cells (FDCs), are able to retain antigenic material on their surfaces for long periods of time. This reservoir declines rapidly with a half-life of about 2 weeks. ... 

A lymph node consists of a cortex and an inner medulla. The cortex is composed of an outer cortex, which contains B-lymphocytes, within lymphoid follicles, and paracortical areas, which contain mainly T-lymphocytes and dendritic cells. The proliferation of B-cells occurs in central areas, called germinal centres. The medulla consists of strings of macrophages and the B-cells that secrete the antibodies (i.e. the effector cells) these are the medullary cords (Figure 17.42). Lymph carries immune cells (e.g. lymphocytes, antigen-presenting cells) and pathogens from the tissues to the lymph nodes, via the afferent lymphatics. 

Figure 31-1 (A) Locations of the primary and secondary tissues of the immune system. The primary lymphoid organs are the thymus, which makes T cells, and the hone marrow, which forms B cells. After moving from these organs into the blood circulation the cells reach one of the secondary lymphoid organs, which include lymph nodes, spleen, tonsils, and Peyer s patches on the small intestine. Immature dendritic cells are found in body tissues including skin and mucous membranes and respond to foreign proteins by inducing attack by T lyphocytes and antibody formation by B cells. (B) Schematic drawing of a lymph node. From Nossal.1 Courtesy of Gustav J. V. Nossal.

Antigen-presenting cells (APCs) are a heterogeneous population of cells with extraordinary immunostimulatory capacity. Some play an important role in the induction of the function of T helper cells and some communicate with other lymphocytes. Cytokines can render the ability to present antigens to various cell types. This results in the expression of MHC class II molecules, which are sometimes lacking on some cells such as endothelial cells. The different types of APCs include macrophages, dendritic cells, B cells and interdigitating cells. APCs are mostly derived from bone marrow and are distributed in lymphoid tissues and in the skin. These three types of major APCs are also called professional APCs. 

Dendritic cells are very important APCs along with mononuclear phagocytes. They are distributed in small quantities in various tissues that come in contact with the external environment including the skin, inner lining of the nose, lungs, stomach and intestine. The blood contains immature dendritic cells. After activation, dendritic cells migrate to the lymphoid tissue to initiate an acquired response following their interaction with lymphoid cells, B and T cells. There are two most common types... 

Circulating dendritic cells Langerhans cells Interdigitating dendritic cells Interstitial dendritic cells Blood, lymph Skin, mucous membrane Secondary lymphoid tissue (with T cells), thymus Gastrointestinal tract, heart, liver, lungs, kidney... 

Lymphoid dendritic cells promote negative selection in the thymus. This may be attributed to their ability to induce fas-mediated apoptosis. Based on their ability to cause apoptosis and their ability to eliminate self-reactive T cells, lymphoid dendritic cells exhibit a regulatory function instead of a stimulatory immune effector function. Myeloid dendritic cells also have differential effects. For example, T cells can be primed to selectively activate THi responses by CD14-derived myeloid dendritic cells. Naive B cells can be activated in the presence of CD40L and IL-2 to secrete IgM by CD34+, CD14-derived myeloid dendritic cells. This effect on naive B cells is not observed with CD la-derived dendritic cells. 

Fig. 7.1 Phases of tissue transplant rejection. The transplanted tissue sheds antigens. These antigens undergo uptake, processing and presentation to the T cells in the secondary lymphoid tissue by APCs, which include macrophages, B cells, Langerhans cells or dendritic cells. This phase results in the production of antibodies and antigen-specific TH and Tc cells. The antibodies and effector cells then migrate to the grafted tissue where TH cells secrete cytokines and which in combination with the antibodies and Tc cells destroy the grafted tissue (see Color Insert)...

Iwasaki A, Kelsall B Location of distinct Peyer s patch dendritic cell subsets and their recruitment by chemokines macrophage inflammatory protein (MIP)-3a, MIP-3 3, and secondary lymphoid organ chemokines. J Exp Med 2000 191 1381-1393. 

CLL/SLL, Chronic lymphocytic leukemia/small lymphocytic lymphoma MCL, mantle cell lymphoma FL, follicular lymphoma MZL/MALT, marginal zone lymphoma/mucosa-associated lymphoid tisuse lymphoma SMZL, splenic marginal zone lymphoma HCL, hairy cell leukemia DLCL, diffuse large-cell lymphoma PCM, plasma cell myeloma BCL-1, cyclin D1 FDC MW, Follicular dendritic cell meshworks CK, cytokeratin LELs, lymphoepitheilal lesions. 

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