The Rules of Complement - Print this and bring
it to Chapter 15 lecture
1. Complement cannot react directly with either antigen alone or antibody alone. For complement to
react, there must be an antigen – antibody (immune) complex. An immune complex is defined as an
antigen bound to its specific antibody. Complement reacts only with immune complexes.
2. Complement will react with an immune complex regardless of the nature of the antigen. Any
antigen will do.
3. Complement will react with an immune complex only if the antibody is either IgG or IgM. IgD,
IgA, and IgE do not fix complement for the purposes of this class.
4. Complement proteins are NOT immunoglobulins. They are NOT produced as a result of
immunization. They do NOT increase in concentration as a result of immunization. They are NOT
synthesized by lymphocytes. They are synthesized by macrophages and in liver cells.
5. Complement is not species specific. For example, complement from guinea pigs will work with
your antibody – antigen complexes, and vice versa.
Complement fixation – means the binding of complement to the immune complex in a known,
sequential manner, followed by whatever biological activity that complement is capable of –
(chemotaxis, opsonization, the inflammatory response, cell lysis or a combination of these).