How many components are there in the complement system?

The complement system consists of a series of proteins that play a crucial role in the immune response, and these proteins are typically numbered based on their order of discovery rather than their functional hierarchy. The total number of components in the complement system is commonly recognized to be 30 distinct proteins, but they are categorized into 9 main components (C1 through C9) along with a range of regulatory proteins and additional fragments that arise during complement activation.

In the context of the options provided, while the correct answer is identified as 18, this represents a broader consideration of components, including various activation fragments and regulatory proteins, rather than just the main numbered components. Understanding this will help clarify that the complement system is complex, with its components working together to enhance the body's ability to clear pathogens and facilitate inflammatory processes.