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Category: Immunology
Hereditary and Acquired Complement Deficiencies, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815905/9781555813642_Chap102-1.gif /docserver/preview/fulltext/10.1128/9781555815905/9781555813642_Chap102-2.gifAbstract:
Complement comprises an interactive system of more than 30 plasma and cell membrane-associated recognition molecules, enzymes, cofactors, control proteins, and receptors. It plays an important role in the host’s response to infection by coating microbial surfaces with complement fragments that enhance uptake and killing by phagocytes. As a major effector arm of the innate immune system, complement serves as a link between many of the activities of acquired immunity and other defense mechanisms, with ties to diverse cell signal responses in an ever-increasing number of tissues. The classical pathway (CP) is critical for the clearance of immune complexes, and it also participates in the removal of apoptotic cells. The phenotype of C1q and other early CP component deficiencies is closely linked to diseases in which these processes are impaired, such as systemic lupus erythematosus (SLE), and rheumatologic disorders such as anaphylactoid purpura, vasculitis, and membranoproliferative glomerulonephritis. The primary synthesis of C1q is by cells of monocyte/macrophage lineage, with follicular dendritic cells as a secondary site. C1q deficiency is an autosomal recessive condition, with deficient patients having little or no detectable protein or C1q function in the circulation. Recombinant or monoclonal antibody complement inhibitors have been used in ischemia-reperfusion injury, cardiopulmonary bypass surgery, and autoimmune disorders. Soluble CR1 acts against the C3 and C5 convertases of both the alternative pathway (AP) and CP, and a humanized anti-C5 monoclonal antibody that prevents cleavage of C5 to C5a and C5b has been effective in animal models and clinical trials.
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CP LP, and AP, of the human complement system, showing the control steps and where some of the biologically active split products are produced.