Multiple complement pathways are activated during coronavirus infection . The complement system is activated in three distinct ways: classical antibody-dependent activation, lectin-dependent activation, and alternative (AP) activation . Regardless of the initial activation steps, the system's primary objective will be to lyse C3. Then C5 is lysed to produce anaphylatoxins (C3a and C5a). They have the potential to induce vasodilation, chemotaxis, and thrombosis . System activation promotes the formation of the membrane attack complex (MAC) (i.e., C5b-9) . Coronaviruses cause the complement system to malfunction. The interaction of the coronavirus's N protein with a membrane-associated serine protease initiates the lectin pathway . By inhibiting factor D or C5, SARS-CoV-2 spike protein (subunits S1 and S2) activates AP and ameliorates immunopathology. Immune complexes and C-reactive protein can also activate the classical pathway . However, some viruses employ distinct strategies for inhibiting and exploiting complement activation . By expressing complement-like regulatory proteins, poxviruses inhibit complement activation . By hijacking complement regulators, flaviviruses impair complement antiviral activity . HIV-1 recruits complement regulators from the host into its virions . The virus can impair the antiviral response by severing the C3 molecule attached to the virus's surface . As a result, SARS-CoV-2 possessed complement-like proteins (such as C1q) that contributed to the activity of invading red blood cells in a complement-complement receptor-dependent manner. When these complement-like C1q proteins were activated, they inadvertently activated C3, activating the complement system.