The effect of anticomplementary substances on properdin in normal and C2-deficient sera

The effect of anticomplementary substances, including zymosan, cobra venom, endotoxin, inulin and immune complexes, on serum properdin concentration and immunoelectrophoretic mobility was studied. In normal serum, zymosan, inulin and immune complexes 'fixed' properdin, while in C2-deficient serum, only zymyosan 'fixed' properdin. Slowly migrating properdin (P) was detected in normal serum following activation by endotoxin and cobra venom but in C2-deficient serum only with cobra venom. Endotoxin did not activate the alternative pathway proteins studied in C2-deficient serum. Fast migrating properdin (P) represented activated properdin and occured as a result of activation of properdin in the Noble agar medium used for electrophoresis provided sufficient cofactors, including Mg2+, were present.