IMMUNOLOGY

Detailed explanation-1: -Complement can be activated through three pathways: classical, lectin, and alternative. The classical pathway is activated when C1q binds to antibody attached to antigen, activating C1r and C1s, which cleave C4 and C2.

Detailed explanation-2: -The classical complement pathway typically requires antigen-antibody complexes for activation (specific immune response), whereas the alternative pathway can be activated by spontaneous complement component 3 (C3) hydrolysis, foreign material, pathogens, or damaged cells.

Detailed explanation-3: -The classical pathway is activated by the binding of antibody molecules (specifically IgM and IgG1, 2 and 3) to a foreign particle. This pathway is antibody-dependent.