Lymphoid follicles

Ansel KM, Ngo VN, Hyman PL, et al. A chemokine-driven positive feedback loop organizes lymphoid follicles. Nature 2000 406 309-314. 

Shi K, Hayashida K, Kaneko M, et al. Lymphoid chemokine B cell-attracting chemokine-1 (CXCL13) is expressed in germinal center of ectopic lymphoid follicles within the synovium of chronic arthritis patients. J Immunol 2001 166(1) 650-655. 

The main site of the mucosal immune system in the gut is referred to as gut-associated lymphoid tissue (GALT), which can be divided into inductive and effector sites. In the small intestine, the inductive sites are in the Peyer s patches, which consist of large lymphoid follicles in the terminal small intestine. The contact with external antibodies triggers a series of cascade events in the body based on immune response (Brandtzaeg et al., 1999). 

Owen, R. L., and Jones, A. L. (1974). Epithelial cell specialization within human Peyer s patches An ultrastructural study of intestinal lymphoid follicles. Gastroenterology 66, 189-203. 

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. 

In view of the high level of infection amongst male homosexuals, it is of interest that lymphoid follicles, equivalent to Peyer s patches are abundant in the human rectal mucosa. 

Antilymphocyte antibody acts primarily on the small, long-lived peripheral lymphocytes that circulate between the blood and lymph. With continued administration, "thymus-dependent" lymphocytes from lymphoid follicles are also depleted, as they normally participate in the recirculating pool. As a result of the destruction or inactivation of T cells, an impairment of delayed hypersensitivity and cellular immunity occurs while humoral antibody formation remains relatively intact. ALG and ATG are useful for suppressing certain major compartments (ie, T cells) of the immune system and play a definite role in the management of solid organ and bone marrow transplantation. 

Gut associated lymphoid tissues (GALT) contain the so-called Peyer s patches which are organized lymphoid follicles with overlying M cells and are considered to be the main entry point for particulate matter during passage down the GI tract (Figure 12.3 and Figure 12.4). 

We now turn to an anatomical description of lymph nodes. The lymph node is surrounded by a thick, fibrous capsule and is subdivided into compartments by trabeculae. Inside the capsule is the subcapsular or marginal sinus, which forms the entry point of lymphatic fluid into the node, via the afferent vessel. The lymph node cortex, which lies beneath the subcapsular sinus, is the location of the primary and secondary lymphoid follicles. The primary follicles are comprised of B-lymphocytes. An immune response stimulates B-cells to replicate and differentiate, converting the primary follicle into a secondary follicle or germinal center, surrounded by a zone of small lymphocytes. The paracortex surrounds the germinal centers and primary follicles and contains mostly T-lymphocytes. The medulla is composed of medullary cords, consisting of macrophages and plasma cells, and medullary sinuses. The medullary vessels include the arteries and veins, and the afferent and efferent lymphatic vessels, respectively, deliver the lymphatic fluid into and out of the lymph node. 

D. E. Bockman, and M. D. Cooper, Pinocytosis by epithelium associated with lymphoid follicles in the bursa of Fabricius, appendix, and Peyer s patches, Am. J. Anat. 136 455 (1973). 

Membranous epithelial cells (Fig. 3), M-cells or microfold cells, ate local ized in regions overlying lymphoid follicles, which are known as Payer s patches... 

R. L. Owen, Sequential uptake of horaeiadiah peroxidase by lymphoid follicle cptheinim of Foyers patches in the neonatal unobstructed mouse intestine on uhrastaucturat study. Gastroenterology 72 440-451 (1977). 

The palpebral conjunctiva is composed of nonkera-tinized stratified epithelium that decreases in thickness as it proceeds from the eyelid margin. Many mucin-secreting goblet cells are located near the fornix. The epithelium overlies the substantia propria, which consists of delicate connective tissue and blood vessels. Most of the immune system cellular components reside in the substantia propria.The stroma contains lymphocytes, lymphoid follicles, neutrophils, plasma cells, and mast cells, all of which proliferate extensively in conjunctival inflammatory disease. This proliferation leads to the formation of papillae and follicles. 

Figure 1 Small airways in COPD patients. The airway wall is thickened and infiltrated with inflammatory cells, predominately macrophages and CD8+ lymphocytes, with increased numbers of fibroblasts. In severe COPD, lymphoid follicles are observed, which consist of a central core of B-lymphocytes, surrounded by T-lymphocytes and are thought to indicate chronic exposure to antigens (bacterial, viral, or autoantigens). Similar changes are also reported in larger airways. The lumen is often filled with an inflammatory exudate and mucus. Peribronchial fibrosis occurs, and it results in progressive and irreversible narrowing of the airway. Airway smooth muscle may be increased slightly.

In sheep wdth mastitis, a chronic inflammation of the mammary gland, and concurrent scrapie, prion infection is present in FDCs and macrophages in lymphoid follicles that develop adjacent to mammary ducts (Ligios et ah, 2005). Although, there are no accounts of prion shedding from colostrum in scrapie-infected sheep without mastitis, macrophages can be shed into the milk of sheep with mastitis. Secretion of the scrapie-infected macrophages in colostrum of sheep with mastitis could potentially play a role in vertical transmission of scrapie since the route of spread from ewe to lamb has not been determined. 

Aluminium causes histological changes at injection sites, and these stain with hematoxylin and eosin (53). Of four patients studied, one had a sclerosing lipogranu-loma-hke reaction with unhned cystic spaces containing crystalline material. Another presented as a large symptomatic subcutaneous swelling, which microscopically showed diffuse and widespread involvement of the subcutaneous tissues by a lymphoid infiltrate with prominent lymphoid follicles. 

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