The complement system involves various proteins (from C1 to C9), factors B,D, H, I, and P, and mannose-binding lectin. C1-C9 are the nine major complement proteins. Properdin (factor P) functions to activate the alternative pathway C3 convertase enzyme. Factors B and D, which are also involved in the alternative pathway, are crucial components involved in complement activation. Factors H and I  help regulate the complement system by regulating the activation process. The MB-lectin pathway is activated when a protein called mannose-binding lectin (MBL) identifies specific carbohydrate patterns on pathogens, which then activates MBL-associated serine proteases (MASPs) to cleave C4 and C2.