Alternative pathway

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It is continuously active, providing the first line of defense against bacterial and viral infections. It is activated by the spontaneous hydrolysis of C3 into C3a and C3b, which forms the C3 convertase (C3bBb). The amplification of the pathway leads to the formation of the C5 convertase, resulting in the formation of the membrane attack complex (MAC) that can lyse the pathogen's membrane.