Activation of the first component of complement.
D000595:Amino Acid Sequence; D000936:Antigen-Antibody Complex / Q000502:physiology; D003166:Complement Activating Enzymes / Q000032:analysis / Q000502:physiology; D003167:Complement Activation; D003172:Complement C1 / Q000032:analysis / Q000502:physiology*; D003174:Complement C1 Inactivator Proteins / Q000502:physiology; D015922:Complement C1q; D015923:Complement C1r; D003173:Complement C1s; D006801:Humans; D007700:Kinetics; D011961:Receptors, Fc / Q000502:physiology
D000936:Antigen-Antibody Complex; D003172:Complement C1; D003174:Complement C1 Inactivator Proteins; D011961:Receptors, Fc; D015922:Complement C1q; D003166:Complement Activating Enzymes; D015923:Complement C1r; D003173:Complement C1s