Freund’s complete adjuvant is a water-in-oil emulsion consisting of a mineral oil, an antibody stimulator such as Mycobacterium tuberculoses, and an emulsifying agent such as lanolin or Arlacel A.” Muramyl dipeptide is a component of the mycobacterial cell wall; it is capable of activating macrophages.
Since activated macrophages are more phagocytic than inactivated macrophages it is more potent than incomplete Freunds adjuvant and used in initial injections. But it is difficult to mix with immunogen and can cause tissue necrosis at the site of injection.
Freunds incomplete adjuvant:
This is similar to complete adjuvant but the oily phase does not contain the killed bacteria.
The small droplets formed in emulsion helps in slow release of antigen from the site of injection, to prolong the exposure period of antigens to the cells of immune system. Typically used for subsequent boosts after initial injection with FCA.