The Vasculitides

© Dirk Biddle

1.7.1 White Blood Cells

White blood cells (leucocytes) form the backbone of the body’s defence system against disease and foreign body invasion. Vasculitis conditions may be defined, at least in part, by determining which leucocytes are present in the blood or surrounding tissue at the site of a vascular inflammation. There are three types of leucocyte: the granulocytes (basophils, eosinophils, neutrophils, and mast cells), the monocytic cells (monocytes which mature into macrophages), and the lymphocytes (T-cells, B-cells, and natural killer cells) (see Fig. 1).

Pluripotent stem cells in bone marrow
differentiate into:
Myeloid stem cells,
which in turn differentiate into:		 Lymphoid stem cells,
which in turn differentiate into:
Granulocytes,
of which types are:
Lymphocytes,
of which types are:
Red blood cells Platelets Basophils Mast cells Eosinophils Neutrophils Monocytes T-cells
B-cells
Nat. killer cells
Macrophages
Helper TH1
Helper TH2
Cytotoxic
Plasma cells
Erythrocytes Thrombocytes Leucocytes (white blood cells)
Blood cell lineage
Fig.1 © Dirk Biddle

back

-------------

Leukocyte: = white blood cell(WBC) a cell which circulates in the blood and lymphatic system and harbours in the lymph glands and spleen. They are part of the immune system responsible for both directly (T-cells and macrophages) and indirectly (B-cells producing antibodies) attacking foreign invaders of the body. They are colourless, lack haemoglobin, contain a nucleus, and include the lymphocytes, monocytes, neutrophils, eosinophils, and basophils. (OMD)

Granulocyte: A polymorphonuclear white blood cell (such as a basophil, eosinophil, or neutrophil) with granule-containing cytoplasm. (M+)

Basophil: A white blood cell with basophilic granules that is similar in function to a mast cell. (M+)

Eosinophil: A white blood cell or other granulocyte with cytoplasmic inclusions readily stained by eosin. (M+)

Neutrophil: A granulocyte that is the chief phagocytic white blood cell.

Mast Cell: A large cell that occurs especially in connective tissue and has basophilic granules containing substances (as histamine and heparin) which mediate allergic reactions. (M+)

Monocyte: A large white blood cell with finely granulated chromatin dispersed throughout the nucleus that is formed in the bone marrow, enters the blood, and migrates into the connective tissue where it differentiates into a macrophage. (M+)

Macrophage: A phagocytic tissue cell of the mononuclear phagocyte system that may be fixed or freely motile, is derived from a monocyte, and functions in the protection of the body against infection and noxious substances. (M+)

Lymphocyte: White cell of the blood that are derived from stem cells of the lymphoid series. Two main classes are recognised, T- and B- lymphocytes, the latter responsible (when activated) for production of antibody, the former subdivided into subsets (helper, suppressor, cytotoxic T-cells) and responsible both for cell-mediated immunity and for stimulating B-cells. (OMD)

T-cells: Any of several lymphocytes (as in helper T-cell) that differentiate in the thymus, possess highly specific cell-surface antigen receptors, and include some that control the initiation or suppression of cell-mediated and humoral immunity (such as by the regulation of T- and B-cell maturation and proliferation) and others that lyse antigen-bearing cells - called also T-lymphocyte. (M+)

B-Cells: A type of lymphocyte normally involved in the production of antibodies to combat infection. It is a precursor to a plasma cell. During infections, individual B-cell clones multiply and are transformed into plasma cells, which produce large amounts of antibodies against a particular antigen on a foreign microbe. This transformation occurs through interaction with the appropriate CD4 T helper cells. (OMD)

Natural Killer Cells: Large granular lymphocytes which do not express markers of either T or B-cell lineage. These cells do possess Fc receptors for IgG and can kill target cells using antibody-dependent cell-mediated cytotoxicity. NK cells can also use perforin to kill cells in the absence of antibody. Killing may occur without previous sensitization. (OMD)