How is the alternative complement pathway activated?

The alternative complement pathway (AP) is activated gradually when a protein called C3 spontaneously breaks down and forms the starting AP C3 convertase, known as C3(H2O)Bb. This occurs when factors B and D are present. This initial step leads to further cleavage of C3 and eventually results in the formation of the AP C3 convertase (C3bBb) and the APC5 convertase (C3bBbC3b). In this process, C3b attaches to factor B, which is then split by factor D into Bb. The resulting C3bBb complex serves as the C3 convertase, leading to the production of additional C3b in a loop which amplifies the response. This activation is then accelerated upon contact with different lipids, proteins,or specific carbohydrate structures found on foreign surfaces such as microorganisms. On a side note, unlike the classical pathway, the alternative pathway doesn't depend on specific interactions between antigens and antibodies to start the process.