The role of a complement system in immune response is to make sure that no bad cells penetrate the immune system. A complement system of immunization might be a series of shots, like booster shots for immunizations.

11

Humans have both an "innate" and an "adaptive" immune system. There are a number of proteins circulating in the blood as part of the complement system that belongs to the innate immune system (although the adaptive system can activate it as well). Normally, the complement proteins are inactive. When the immune system detects some threat, the complement system is triggered and the circulating proteins are chemically split into smaller components. C3 convertases are chemicals that cleave C3 complement into breakdown products in both the "classical" and the "alternative" pathways of the complement system.

Complement is a protein made in the innate immune system that embeds itself in the membrane of bacteria, leaving a hole through which the cytoplasm escapes killing the bacterial cell.

Be sure at the outset to get your mind around the idea that the complement system is a set of over 20 different protein molecules always found in the blood.