C3bBb is a complex formed during the complement system activation, which is part of the immune response. It consists of the protein C3b and the enzyme factor Bb. This complex plays a crucial role in the alternative pathway of complement activation, helping to amplify the immune response against pathogens. When C3bBb is formed, it acts as a convertase, facilitating the cleavage of more C3 proteins into C3a and C3b. This process enhances opsonization, marking pathogens for destruction, and promotes inflammation, which helps recruit immune cells to the site of infection.