Figure 5.

Schematic representation of the complement pathway. (A) Three parallel arms of the complement pathway: the classical pathway, the lectin pathway, and the alternative pathway converge on the level of the C3 that is cleaved by C3 convertase (C4bC2a in the classical and lectin pathway, or C3-H2OBb in the alternative pathway) into C3a anaphylotoxin and C3b. C3aR binds C3a. C3b is recruited to form C5 convertase, which processes inactive C5 into C5a anaphylotoxin and C5b. C5aR binds C5a. All three pathways are regulated by Serping1 or C1 inhibitor. (B) Schematic representation of Serping1 cell-autonomous and non-cell autonomous roles in migrating neurons. Serping1 is expressed and secreted by neurons and inhibits complement pathway by direct interaction with C1s, C1r, Masp1, and Masp2. Serping1 functions in the extracellular matrix and influences both the neuron it was secreted from and neighboring neurons.