Page 257 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 19 Overview and Compartmentalization of the Immune System 209

follicles in the spleen and serves as the major route of entry of SUGGESTED READINGS
blood-borne antigens and lymphocytes from the blood into the white
pulp. Unlike other organs that have a closed vascular circulation in Akira S, Uematsu S, Takeuchi O: Pathogen recognition and innate immunity.
which blood travels from arterial to venous circulation through capil- Cell 124:783, 2006.
lary beds, branches of the splenic artery penetrate the white pulp, Belardelli F, Ferrantini M: Cytokines as a link between innate and adaptive
forming an open sinusoidal network termed the marginal sinuses. antitumor immunity. Trends Immunol 23:201, 2002.
From the marginal sinuses, blood filters through the white pulp Borregaard N: Neutrophils, from marrow to microbes. Immunity 33:657,
regions of the spleen and encounters resident B and T cells. Following 2010.
this encounter, the blood is drained via branches of the splenic vein, Bottazzi B, Doni A, Garlanda C, et al: An integrated view of humoral innate
but an efferent lymphatic circulation also collects and drains the immunity: pentraxins as a paradigm. Annu Rev Immunol 28:157, 2010.
spleen. Beyond the white pulp, the splenic artery sends additional Cheroutre H: IELs: Enforcing law and order in the court of the intestinal
branches into the red pulp for further blood antigen surveillance and epithelium. Immunol Rev 206:114, 2005.
filtration that is accomplished by macrophages. Gowthaman U, Chodisetti SB, Agrewala JN: T cell help to B cells in germinal
In addition to LNs and the spleen, there are numerous other centers: Putting the jigsaw together. Int Rev Immunol 29:403, 2010.
29
sites of secondary lymphoid tissue. A critical part of the second- Greaves DR, Gordon S: The macrophage scavenger receptor at 30 years of
ary lymphoid system is the mucosa-associated lymphatic tissue age: Current knowledge and future challenges. J Lipid Res 50:S282, 2009.
(MALT). As the name implies, the MALT is in physical proximity Josefowicz SZ, Lu LF, Rudensky AY: Regulatory T cells: mechanisms of
with the mucosa (i.e., the epithelium and associated connective differentiation and function. Annu Rev Immunol 30:531, 2012.
tissue that line the surfaces of the body). MALT is found at sites Misch EA, Hawn TR: Toll-like receptor polymorphisms and susceptibility to
where antigens most commonly breach these epithelial barriers: the human disease. Clin Sci 114:347, 2008.
gastrointestinal, respiratory, and genitourinary tracts. In some Papayannopoulos V, Zychlinsky A: NETs: A new strategy for using old
tissues, the MALT forms relatively large structures that can be weapons. Trends Immunol 30:513, 2009.
clearly distinguished histologically, such as the Peyer patches in the Sansonetti PJ: To be or not to be a pathogen: That is the mucosally relevant
ileum and in the lymphoid tissue under the epithelium of the question. Mucosal Immunol 4:8, 2011.
appendix. In these sites, perhaps because of the constant stimula- Steinman L: A brief history of T(H)17, the first major revision in the
tion by microbial pathogens in the intestine, the MALT resembles T(H)1/T(H)2 hypothesis of T cell-mediated tissue damage. Nat Med
lymphatic tissue in the spleen and LNs, with well-demarcated 13:139, 2007.
primary and secondary follicles that contain primarily B cells and Trinchieri G, Sher A: Cooperation of Toll-like receptor signals in innate
intervening T cell–rich zones. immune defence. Nat Rev Immunol 7:179, 2007.
In other tissues, such as the genitourinary tract and the salivary Turvey SE, Hawn TR: Towards subtlety: Understanding the role of Toll-like
glands, the microscopic anatomy of the MALT may not be as well receptor signaling in susceptibility to human infections. Clin Immunol
defined as seen in Peyer patches; but the stromal tissue underlying 120:1, 2006.
the epithelium contains numerous lymphocytes and APCs. These van de Vosse E, van Dissel JT, Ottenhoff THM: Genetic deficiencies of
sites provide an additional compartment of secondary lymphoid innate immune signalling in human infectious disease. Lancet Infect Dis
tissue where antigens can accumulate, be processed, and be presented 9:688, 2009.
to lymphocytes to stimulate an adaptive immune response. Villasenor J, Benoist C, Mathis D: AIRE and APECED: Molecular insights
Whereas the MALT constitutes a lymphoid population beneath into an autoimmune disease. Immunol Rev 204:156, 2005.
the surface epithelium, a separate population of lymphocytes, primar- Walker JA, Barlow JL, McKenzie AN: Innate lymphoid cells—how did we
ily T cells, traffics directly through the epithelium in certain tissues, miss them? Nat Rev Immunol 13:75, 2013.
such as the gastrointestinal tract. These intraepithelial lymphocytes
(IELs) include αβ T cells and γδ T cells, and comprise 1 in every
5 to 10 cells in the intestinal epithelium. Because the lining of the REFERENCES
intestine is the largest organ surface area of the body, IELs are one of
the largest T-cell populations. These IEL T cells are composed of For the complete list of references, log on to www.expertconsult.com.
different subpopulations, some of which are conventional T cells that
recognize foreign antigens; others are regulatory T cells that limit the
extent of an immune response and maintain immune homeostasis, a
critical function in the antigen-rich milieu of the gut. 30