Haematologia 17. (1984)

1984 / 1. szám - Dierich, M. P. - Schulz, T.: Physiological and pathological effects of activated complement

Haematologia 17 (1), pp. 3—16 (1984) Physiological and Pathological Effects of Activated Complement M. P. Dierich,1 Th. Schulz2 Institut für Hygiene, Universität Innsbruck,1 Fritz-Pregl Str. 3., A-6010 Innsbruck, Austria; Institut für Medizinische Mikrobiologie, Johannes Gutenberg-Universität,2 Augustusplatz, D-6500 Mainz, FRG (Received 20 January 1983; accepted 18 February 1983) In this short review of our present understanding of the complement system the emphasis is on a synopsis of the biological aspects of the various complement components, their fragments and complexes. For this reason we decided to refer to a number of reviews where certain aspects are dealt with extensively.* Keywords: alternative pathway, classical pathway, complement, complement receptors. * At the turn of the century complement was thought to consist of one heat labile factor. Today we know about 20 different complement components. They belong to one of the following groups: 1. The classical pathway of C activation (CPCA): Clq, r, s, C4, C2, C3. 2. The alternative pathway of complement activation (APCA): C3b, B, D. 3. The terminal complement sequence: C5, C6, C7, C8, C9. 4. The group of enhancing or inhibiting modulators of the complement sequence: e.g. P, H, I, Cl INA and others. In Table 1 standard physico-chemical characteristics of the components are listed. CPCA is triggered by the ‘activated’ Fc portion of antibodies contained in aggregates of antibodies or in immune complexes. The CH2 domain of IgG binds Clq by its globular heads. Clq is either part of an intact Cl, which consists of Clr and Cls in addition to Clq, the whole complex being held together by Ca++ or the bound Clq fixes Clr and Cls sequentially. Following binding, Clr is cleaved and in turn cleaves and thus activates Cls [3, 4]. The resulting esterase activates C4 and C2 yielding a complex of C4b and C2a, the C3 convertase of the classical pathway. C4b binds C3 so that it can be cleaved by C2a into C3b and C3a. If C3a is deposited sufficiently close to C2a and C4b, the three components together form a complex, the C5 convertase, with C2a as the enzymatic centre. C5 is cleaved into C5a and C5b. It should be mentioned that the classical pathway can be started * For the nomenclature of the components and their reaction products we follow the WHO recommendation [1, 2]. 1* Haematologia 17, 1984

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