The following are some definitions of terms commonly used in discussing complement:

            C-activation: alteration of C proteins, enabling them to interact with another component

            C-fixation: utilization of C by antigen-antibody complexes

            Hemolytic unit (CH₅₀): dilution of serum that will lysis 50% of a standard amount of antibody-coated erythrocytes

           C-inactivation:  denaturation (usually by heat) of an early complement component resulting in loss of hemolytic activity

            Convertase/esterase:  altered C protein which acts as a proteolytic enzyme for another C component

      The following are some conventions of complement nomenclature:

                                                                                                      _{___}

            Activated components of complement are over-lined (e.g. C1qrs)

            When enzymatically cleaved, the larger fragment binds to the activation complex or membrane and the smaller fragment is released into the microenvironment.  The letter “b” is usually added to name of the larger membrane-binding fragment and the letter “a” to the smaller fragment ( e.g. C3b and C3a).  The exception is for C2 in which the larger membrane-binding fragment is given the “a” designation and the smaller fragment is given the “b” designation.