The functional inhibition of activated C1 inhibitor in normal human serum causes spontaneous consumption of the complement components C2, C3, C4, and factor B.
The human complement components C1r, C1s, C4, C3, factor B, and/or activated C1INH were functionally blocked in normal human serum (NHS) and EGTA- or EDTA-treated NHS by polyclonal monospecific Fab'-fragments to the individual components. The results of inhibition experiments are compatible with the formation of a classical pathway fluid-phase C3 convertase (C4b2a) spontaneously generated by the inhibition of activated C1INH. This process in both NHS and EGTA-NHS was accompanied by the consumption of C2, C4, C3, and factor B but only by poor enhancement of C5 conversion. Blocking subcomponent C1r, completely inhibited spontaneous activation of the complement components, indicating that the control of C1r hydrolysis is the essential role of activated C1INH as a regulator of C1 activation in NHS. Non-complement serum proteases were inactive during the initiation of the activation process. The presence of blood cells during functional inhibition of activated C1INH in NHS slightly decreased the consumption of C3 but not of C2 and C4.
D000799:Angioedema / Q000235:genetics / Q000276:immunology; D003166:Complement Activating Enzymes / Q000378:metabolism; D003167:Complement Activation; D003174:Complement C1 Inactivator Proteins / Q000037:antagonists & inhibitors* / Q000276:immunology; D015923:Complement C1r; D003175:Complement C2 / Q000378:metabolism; D003176:Complement C3 / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism; D003182:Complement C5 / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism*; D003171:Complement Pathway, Classical; D003165:Complement System Proteins / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology
D003174:Complement C1 Inactivator Proteins; D003175:Complement C2; D003176:Complement C3; D003181:Complement C4; D003182:Complement C5; D004792:Enzyme Precursors; D007140:Immunoglobulin Fab Fragments; D003165:Complement System Proteins; D003166:Complement Activating Enzymes; D015923:Complement C1r; D011415:Complement Factor B