Where are complement proteins predominantly found in the body?

Complement proteins are predominantly found in the blood. They circulate in the bloodstream in an inactive form and are part of the innate immune system. When activated, these proteins play a crucial role in enhancing the ability of antibodies and phagocytic cells to clear pathogens from an organism. Activation of the complement system leads to various immune responses, including opsonization, which helps mark pathogens for destruction, and the formation of the membrane attack complex that can directly lyse bacterial cells.

While complement proteins can be present in lower concentrations in tissues, lymphatic fluid, and the extracellular matrix, their primary reservoir is indeed the blood. This allows for widespread distribution throughout the body to quickly respond to infections or the presence of foreign substances.