South Parks Road, Oxford OX1 3QU, UK. The complement system in blood plasma is a major mediator of innate immune defence. The function of complement is ...
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Biochemical Society Transactions (2000) Volume 28, Part 5
2202 Serine proteases of the complement system R.B. Sim, A. Laich. MRC Immunochemistry Unit, Department of Biochemistry, South Parks Road, Oxford O X 1 3QU, UK. The complement system in blood plasma is a major mediator of innate immune defence. The function of complement is to recognise, then opsonise or lyse, particulate materials including bacteria, yeasts, and other microrganisms, host cell debris and altered host cells. Recognition occurs by binding of complement proteins to charge or saccharide arrays. After recognition, a series of serine proteases is activated, culminating in the assembly of complex unstable proteases called C3/C5 convertases. These activate the complement protein C3, which binds covalently to the activator particle, and acts as an opsonin. C5 is also activated, and forms a multiprotein membrane attack complex with C6, C7, C8 and C9, which damages any lipid bilayer membrane in the activator particle. Excessive or inappropriate complement activation contributes to inflammatory damage to host tissue. The complement serine proteases include the closely-related Clr, Cls, MASPI, MASP2 (80-90 kDa), C2 and Factor B (lOOkDa), Factor D (25kDa) and Factor I (85kDa). Each of these has unusually restricted specificity, and low enzymic activity. The Clr, C l s and MASP group occur as proenzymes. When activated, they are regulated, like many plasma serine proteases, by a serpin, C1-inhibitor. C2 and Factor B, however, have complex multiple regulation by a group of complement proteins called the Regulation of Complement Activation (RCA) proteins, while Factors I and D, which circulate as active enzymes, appear to have no natural inhibitors. Advances in structure determination and protein-protein interaction properties are gradually leading to a detailed understanding of the complement system proteases and indicating possible new routes for potential therapeutic control of complement
2204 Signaling pathways in the Drosophila immune response JM. Reichhart UPR CNRS 9022 IBMC 15, rue R.Descartes 67084 Strasbourg France Drosophila is able t o mount an efficient immune response when challenged by septic injury. The response is complex and involves cellular and humoral reactions which culminate in phagocytosis of invading microorganisms and/or their destruction by lytic peptides. A keystone in the regulation of many of these defense mechanisms is the transmembrane receptor Toll. Current evidence strongly suggests that recognition of infectious non-self in Drosophila is not directly mediated by Toll, but results from interaction of Toll with a processed form of the protein Spaetzle. This processing itself is dependent o n a proteolytic cascade probably induced by binding of microbial wall components to upstream pattern recognition proteins. Activated Toll controls immune gene expression via a signaling cascade strongly reminiscent of NF-KB activation in mammals. O u r current understanding of the mechanism of this activation will be reviewed. Additional signaling pathways are required for a full host response. These pathways and their cross-talks with the Toll activation cascade will be analysed in the presentation.
2205 Toll-like receptors: lessons from knockout mice Shizuo Akira Department of Host Defense, Research Institute for Microbial Diseases, CREST, Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan
2203 Complement deficiency, apoptosis and autoimmunity M.Botto Imperial College School of Medicine, Hammersmith Campus, London The strongest susceptibility genes for the development of systemic lupus erythematosus (SLE) in humans are null mutants of classical pathway complement proteins. There is a hierarchy of disease susceptibility and severity according t o the position of the missing protein in the activation pathway, with the severest disease associated with C l q deficiency. Apoptotic cells, which express o n their surface blebs of the typical autoantigens of SLE, have been demonstrated t o bind C l q . To investigate the role of the individual complement components in the clearance of apoptotic cells we developed novel in vivo apoptotic cell phagocytosis assays. Both C l q - and C4-deficient mice exhibited a defect in the phagocytosis of apoptotic cells by inflammatory macrophages, however, the defect was significantly more pronounced in the Clq-deficient animals. In addition, human Clq-deficient macrophages showed a similar defect in the phagocytic uptake of apoptotic cells in viiro. The defect was rectified by adding purified human C l q . These results constitute the first demonstration of an impairment in the phagocytosis of apoptotic cells by macrophages in vim in a mammalian system. These findings may also explain the link between hereditary complement deficiency and the development of SLE.
0 2000 Biochemical Society
Toll in Drorophila is a receptor that is required for dorsoventral polarity during development, and also involved in host defense against fungal infection. Recently, mammalina homologues of Toll, designated as Toll-like receptors(TLRs) have been identified. The TLR family harbors an extracellular leucine-rich repeat(LRR) domain and a cytoplasmic domain that is homologous t o that of the IL-1R family. Analogous to the IL-lR, T L R recruits IRAK via adaptor MyD88, and then induce activation of TRAF6, N I K and finally NF-KB. I n order t o examine the role of T L R family, we have generated mice lacking TLR2, TLR4, and MyD88. TLR4 mice are hyporesponsive to LPS, while TLR2 K O mice are hyporesponsive to peptidoglycan from Gram-positive bacteria, and lipoproteins, but not to LPS. MyD88 K O mice are unresponsive t o all bacterial cell wall components tested, including LPS, peptidoglycan, lipoteichoic acids, and Mycobacterium tuberculosis whole cell lysates. Taken together, these results demonstrate that responses to bacterial cell wall components are differentially mediated by TLR2 and TLR4, and MyD88 is essential t o responses t o all bacterial cell wall components. However, LPS activation of M A P kinases and NF-KB remains intact in MyD88-deficient macrophages. This indicates that the LPS response is mediated by both MyD88-dependent and -independent pathways, and that the MyD88-dependent pathway is essential for cytokine production mediated by LPS. I will discuss the nature of the MyD88-independent pathway.
