<prompt> Which complement component is involved in both classical and alternative pathways -C1C2C3C4  <response>: - the central process in the complement cascade is the activation of C3. - in classical pathway, activation of C3 is achieved by C4b2a classical C3 convease . - the activation of C3 without prior paicipation of C4b2a is known as alternative pathway. Reference : Anathanarayan panikers 9th edition, pg no: 122,123 p 