Histiocytosis class I and II

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  1. samuel

    samuel New Member

    Histiocytosis class I and II

    Also in 1987, as a result of the collaborative efforts, a simple stratification system for practical use was introduced for LCH. The Writing Group of the Histiocyte Society recommended a division of the histiocytic disorders into three classes: Langerhans cell histiocytosis (LCH) (class I); non-Langerhans cell histiocytosis (class II); and malignant histiocytic disorders (class III). A minor revision of this classification has more recently been proposed, and the three major groups are now termed (1) dendritic cell-related disorders (of which LCH is by far the most common), (2) macrophage-related disorders, and (3) malignant disorders.

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    three classes based on the pathologic cells
    present within the lesions.
    •Class I: Langerhans cell histiocytoses and other dendritic
    cell disorders.
    •Class II: non-Langerhans cell histiocytoses primarily con-sisting of hemophagocytic lymphohistiocytosis.
    •Class III: malignant histiocytosis.
    This system was revised in 1997 by the World Health
    Organization’s Committee on Histiocytic/Reticulum Cell
    Proliferations and the Reclassification Working Group of the
    Histiocyte Society. The central theme of this reclassification
    schema consisted of distinguishing the clearly malignant
    histiocytoses from the remaining subtypes, the so-called “dis-orders of varied biological behavior”. Acute myelomonocytic
    leukemia (FAB M4), acute monocytic leukemia (FAB M5),
    chronic myelomonocytic leukemia and the histiocytic sarco-mas are all classified in the malignant histiocytoses category.
    The disorders of varied biological behavior continued to be
    divided into dendritic cell-related disorders (class I) and
    macrophage-related disorders (class II). The dendritic cell-related disorders include Langerhans cell histiocytosis, the
    most common type in this class, in addition to other less
    common subtypes. Primary and secondary hemophagocytic
    lymphohistiocytosis, in addition to sinus histiocytosis with
    massive lymphadenopathy (also known as Rosai–Dorfman
    disease), are the two major types of macrophage-related his-tiocytosis discussed in this chapter. This classification schema
    is summarized in Table 15.1.
    Table 15.1Classification of histiocytic disorders.
    Class I: dendritic cell histiocytoses
    Langerhans cell histiocytosis
    Secondary dendritic cell processes
    Juvenile xanthogranuloma and related disorders
    Erdheim–Chester disease
    Solitary histiocytomas of various dendritic cell phenotypes
    Class II: nondendritic cell histiocytoses
    Primary hemophagocytic lymphohistiocytosis
    Familial hemophagocytic lymphohistiocytosis
    Secondary hemophagocytic lymphohistiocytosis
    Infection associated
    Malignancy associated
    Rosai–Dorfman disease (sinus histiocytosis with massive lymphadenopathy)
    Solitary histiocytoma with macrophage phenotype
    Class III: malignant histiocytoses
    Monocyte related
    Leukemias ( FAB and revised FAB classification)
    Monocytic leukemia M5A and M5B
    Acute myelomonocytic leukemias M4
    Chronic myelomonocytic leukemias
    Extramedullary monocytic tumor or sarcoma
    Dendritic cell-related histiocytic sarcoma
    Macrophage-related histiocytic sarcoma
    FAB, French–American–British.



    In 1973 Nezelof et al.
    22
    provided definitive evidence for
    the phenotypic similarity of normal Langerhans cells and
    LCH cells, including a description of the presence of Birbeck
    granules in both cell types. However, LCH cells, in contrast to
    normal Langerhans cells, typically lack dendritic cell exten-sions and have a rounded appearance with distinct cellular
    margins. These cells express CD1a, S100 and Langerin (CD207)
    but not the typical markers of more mature dendritic cells
    such as CD83, CD86 and DC-Lamp (Fig. 15.2). In addition,
    these cells express CD40 and intracellular MHC class II pro-teins but are inefficient antigen-presenting cells. When LCH
    cells are exposed in vitro to CD40L they acquire markers of
    dendritic cell maturation.
    23
    LCH cells also express CCR6, the
    receptor for the proinflammatory chemokine CCL20/MIP3α,
    a characteristic of immature dendritic cells. Furthermore,
    these cells have been shown to also secrete CCL20/
    MIP3α, CCL5/RANTES and CXCL11/I-TAC, all of which
    are believed to function in recruiting additional LCH
    cells, eosinophils and T cells to LCH lesions.
    12
    Of note, the
    co-expression of CCR6 and CCR7 on LCH cells has also
    been reported.

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