Interaction of zymosan and of activated properdin with factor D-depleted guinea pig serum: implications for the mechanism of initial C3 cleavage via the alternative complement pathway.
Factor D of the alternative C pathway was specifically removed from guinea pig serum. The resulting serum reagent (RD) supported neither the formation of a C3-cleaving enzyme on zymosan (Z) nor the inactivation of C3 or of factor B in the presence of Z or activated properdin (P). Addition of purified D to RD restored these properties. Studies were limited amounts of purified D were added to RD with Z or P as activating substances, gave the following results: (1) Inactivation of B and of C3 occurs in the presence of minute amounts of D. (2) C3 inactivation is more efficient than B inactivation and proceeds even in the absence of detectable enzymatic B activation. (3) C3 cleavage at any D concentration tested is always accompanied by uptake of C3 fragments onto Z. With respect to initial C3 cleavage via the alternative C pathway these data suggest that the initiating reaction is D-dependent, very efficient in depositing C3 fragments on particulate activating substances such as Z and able to utilize factor B in an apparently uncleaved form.
D000818:Animals; D003176:Complement C3 / Q000378:metabolism*; D003165:Complement System Proteins / Q000378:metabolism* / Q000502:physiology*; D006168:Guinea Pigs / Q000276:immunology; D007106:Immune Sera; D011414:Properdin / Q000302:isolation & purification / Q000502:physiology*; D015054:Zymosan / Q000502:physiology*
D003176:Complement C3; D007106:Immune Sera; D011414:Properdin; D003165:Complement System Proteins; D015054:Zymosan