The mantle zone of a lymphatic nodule is an outer ring of small lymphocytes surrounding a germinal center. It is known as the "corona", it contains transient lymphocytes. It is the location of the lymphoma in mantle cell lymphoma. Mantle zone expansion may be seen in benign, such as Castleman disease, malignancy, i.e. Mantle cell lymphoma. Tcl-1 is expressed in the mantle zone. Https://web.archive.org/web/20080813003821/http://erl.pathology.iupui.edu/HISTO/LABE109. HTM Histology image: 07102loa – Histology Learning System at Boston University — "Lymphoid Tissues and Organs: lymph node and medulla"
A lymphocyte is one of the subtypes of a white blood cell in a vertebrate's immune system. Lymphocytes include natural killer cells, T cells, B cells, they are the main type of cell found in lymph, which prompted the name "lymphocyte". The three major types of lymphocyte are B cells and natural killer cells. Lymphocytes can be identified by their large nucleus. T cells and B cells are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity, whereas B cells are responsible for humoral immunity; the function of T cells and B cells is to recognize specific "non-self" antigens, during a process known as antigen presentation. Once they have identified an invader, the cells generate specific responses that are tailored to maximally eliminate specific pathogens or pathogen-infected cells. B cells respond to pathogens by producing large quantities of antibodies which neutralize foreign objects like bacteria and viruses. In response to pathogens some T cells, called T helper cells, produce cytokines that direct the immune response, while other T cells, called cytotoxic T cells, produce toxic granules that contain powerful enzymes which induce the death of pathogen-infected cells.
Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered, in the form of memory cells. Throughout the lifetime of an animal, these memory cells will "remember" each specific pathogen encountered, are able to mount a strong and rapid response if the same pathogen is detected again. NK cells are a part of the innate immune system and play a major role in defending the host from tumors and virally infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing changes of a surface molecule called MHC class I. NK cells are activated in response to a family of cytokines called interferons. Activated NK cells release cytotoxic granules which destroy the altered cells, they are named "natural killer cells" because they do not require prior activation in order to kill cells which are missing MHC class I. Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow; this process is called haematopoiesis.
All lymphocytes originate, during this process, from a common lymphoid progenitor before differentiating into their distinct lymphocyte types. The differentiation of lymphocytes follows various pathways in a hierarchical fashion as well as in a more plastic fashion; the formation of lymphocytes is known as lymphopoiesis. B cells mature into B lymphocytes in the bursa equivalent, which in humans is the GALT, thought to be located in the Peyer's patches of the intestine, while T cells migrate to and mature in a distinct organ, called the thymus. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs where they survey for invading pathogens and/or tumor cells; the lymphocytes involved in adaptive immunity differentiate further after exposure to an antigen. Effector lymphocytes function to eliminate the antigen, either by releasing antibodies, cytotoxic granules or by signaling to other cells of the immune system. Memory T cells remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure.
Microscopically, in a Wright's stained peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no eosinophilic cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is the size of a red blood cell; some lymphocytes show a clear perinuclear zone around the nucleus or could exhibit a small clear zone to one side of the nucleus. Polyribosomes are a prominent feature in the lymphocytes and can be viewed with an electron microscope; the ribosomes are involved in protein synthesis, allowing the generation of large quantities of cytokines and immunoglobulins by these cells. It is impossible to distinguish between B cells in a peripheral blood smear. Flow cytometry testing is used for specific lymphocyte population counts; this can be used to determine the percentage of lymphocytes that contain a particular combination of specific cell surface proteins, such as immunoglobulins or cluster of differentiation markers or that produce particular proteins.
In order to study the function of a lymphocyte by virtue of the proteins it generates, other scientific techniques like the ELISPOT or secretion assay techniques can be used. In the circulatory system, they move from lymph node to lymph node; this contrasts with macrophages. A lymphocyte count is part of a peripheral complete blood cell count and is expressed as the percentage of lymphocytes to the total number of white blood cells counted. A general increase in the number of lymphocytes is known as lymphocytosis, whereas a decrease is known as lymphocytopenia. An increase in lymphocyte concentration is a sign of a viral infection. A high lymphocyte count wi
A T cell, or T lymphocyte, is a type of lymphocyte that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells, by the presence of a T-cell receptor on the cell surface, they are called T cells. The several subsets of T cells each have a distinct function; the majority of human T cells, termed alpha beta T cells, rearrange their alpha and beta chains on the cell receptor and are part of the adaptive immune system. Specialized gamma delta T cells, have invariant T-cell receptors with limited diversity, that can present antigens to other T cells and are considered to be part of the innate immune system. Effector cells are the superset of all the various T cell types that respond to a stimulus, such as co-stimulation; this includes helper, killer and other T cell types. Memory cells are their opposite counterpart that are longer lived to target future infections as necessary. T helper cells assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, activation of cytotoxic T cells and macrophages.
These cells are known as CD4+ T cells because they express the CD4 glycoprotein on their surfaces. Helper T cells become activated when they are presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presenting cells. Once activated, they divide and secrete small proteins called cytokines that regulate or assist in the active immune response; these cells can differentiate into one of several subtypes, including TH1, TH2, TH3, TH17, TH9, or TFH, which secrete different cytokines to facilitate different types of immune responses. Signalling from the APC directs T cells into particular subtypes. Cytotoxic T cells destroy virus-infected cells and tumor cells, are implicated in transplant rejection; these cells are known as CD8+ T cells since they express the CD8 glycoprotein at their surfaces. These cells recognize their targets by binding to antigen associated with MHC class I molecules, which are present on the surface of all nucleated cells. Through IL-10, other molecules secreted by regulatory T cells, the CD8+ cells can be inactivated to an anergic state, which prevents autoimmune diseases.
Antigen-naïve T cells expand and differentiate into memory and effector T cells after they encounter their cognate antigen within the context of an MHC molecule on the surface of a professional antigen presenting cell. Appropriate co-stimulation must be present at the time of antigen encounter for this process to occur. Memory T cells were thought to belong to either the effector or central memory subtypes, each with their own distinguishing set of cell surface markers. Subsequently, numerous new populations of memory T cells were discovered including tissue-resident memory T cells, stem memory TSCM cells, virtual memory T cells; the single unifying theme for all memory T cell subtypes is that they are long-lived and can expand to large numbers of effector T cells upon re-exposure to their cognate antigen. By this mechanism they provide the immune system with "memory" against encountered pathogens. Memory T cells may be either CD4+ or CD8+ and express CD45RO. Memory T cell subtypes: Central memory T cells express CD45RO, C-C chemokine receptor type 7, L-selectin.
Central memory T cells have intermediate to high expression of CD44. This memory subpopulation is found in the lymph nodes and in the peripheral circulation.. Effector memory T cells lack expression of CCR7 and L-selectin, they have intermediate to high expression of CD44. These memory T cells lack lymph node-homing receptors and are thus found in the peripheral circulation and tissues. TEMRA stands for terminally differentiated effector memory cells re-expressing CD45RA, a marker found on naive T cells. Tissue resident memory T cells occupy tissues without recirculating. One cell surface marker, associated with TRM is the integrin αeβ7. Virtual memory T cells differ from the other memory subsets in that they do not originate following a strong clonal expansion event. Thus, although this population as a whole is abundant within the peripheral circulation, individual virtual memory T cell clones reside at low frequencies. One theory is. Although CD8 virtual memory T cells were the first to be described, it is now known that CD4 virtual memory cells exist.
Regulatory T cells are crucial for the maintenance of immunological tolerance. Their major role is to shut down T cell-mediated immunity toward the end of an immune reaction and to suppress autoreactive T cells that escaped the process of negative selection in the thymus. Suppressor T cells along with Helper T cells can collectively be called Regulatory T cells due to their regulatory functions. Two major classes of CD4 + Treg cells have been described -- FOXP3 − Treg cells. Regulatory T cells can develop either during normal development in the thymus, are known as thymic Treg cells, or can be induced peripherally and are called peripherally derived Treg cel
Reed–Sternberg cells are distinctive, giant cells found with light microscopy in biopsies from individuals with Hodgkin's lymphoma. They are derived from B lymphocytes, classically considered crippled germinal center B cells, meaning they have not undergone hypermutation to express their antibody. Seen against a sea of B cells, they give the tissue a moth-eaten appearance. Reed–Sternberg cells are large and are either multinucleated or have a bilobed nucleus with prominent eosinophilic inclusion-like nucleoli. Reed–Sternberg cells are CD30 and CD15 positive negative for CD20 and CD45; the presence of these cells is necessary in the diagnosis of Hodgkin's lymphoma – the absence of Reed–Sternberg cells has high negative predictive value. The presence of these cells is confirmed by use of biomarkers in immunohistochemistry, they can be found in reactive lymphadenopathy and rarely in other types of non-Hodgkin lymphomas. Anaplastic large cell lymphoma may show RS-like cells as well, they are named after Dorothy Reed Mendenhall and Carl Sternberg, who provided the first definitive microscopic descriptions of Hodgkin's disease.
A special type of Reed–Sternberg cells is the lacunar histiocyte, whose cytoplasm retracts when fixed in formalin, so the nuclei give the appearance of cells that lie with empty spaces between them. These are characteristic of the nodular sclerosis subtype of Hodgkin's lymphoma. Mummified RSCs are associated with classical Hodgkin's lymphoma while popcorn cells are lymphohistiocytic variant of Reed Sternberg cells and are associated with nodular lymphocyte predominant Hodgkin's lymphoma. RSCs and one RSC cell line but not other RSC cell lines express high levels of ALOX15 or ALOX15B, enzymes that metabolize arachidonic acid and various other polyunsaturated fatty acids to a wide array of bioactive products including in particular those of the 15-Hydroperoxyeicosatetraenoic acid family of arachidonic acid metabolites; this is unusual in that lymphocytes express little or no ALOX15. It is suggested that ALOX15 and/or ALOX15B operating through one of its arachidonic acid-derived products, the eoxins, contributes to the development and/or morphology of Hodgkin's lymphoma.
Non-Hodgkin lymphoma Hodgkin's lymphoma