What is Freund's Complete Adjuvant?

Freund’s complete adjuvant immunopotentiator is a solution that is used to boost the response of the immune system to a foreign substance. It consists of inactivated or dried bacteria, usually of the Mycobacterium tuberculosis or Mycobacterium butyricum species. Through these mycobacterial components, Freund’s complete adjuvant antigen contents help improve and prolong an immune response. This adjuvant is sometimes called Jules T. Freund complete adjuvant, in honor of Jules T. Freund, an American immunologist.

Adjuvant is a general term used to refer to agents used in producing antibodies. In order to produce antibodies, a laboratory mammal such as a mouse or rabbit undergoes immunization. The immunizing solution contains the antigens and the adjuvant. These antigens induce immune cells called bursa-derived (B) cells to proliferate and produce immunoglobulins, or antibodies, that specifically target the antigens. The antibodies produced through this process are polyclonal, which means they are derived from different B cells.

There are two kinds of Freund’s adjuvant. The first is Freund’s complete adjuvant mineral oil-containing solution. This kind is a water-in-oil emulsion, localizes antigens for release for about 6 months. It also contains a surfactant called mannide monooleate and heat-killed mycobacteria. The second type is called Freund’s incomplete adjuvant does not contain mycobacteria and is less effective.

In general, the Freund’s complete adjuvant stimulates the immune system in two different ways. First, Freund’s complete adjuvant acts as a surfactant that allows the protein antigens to become concentrated over large surface areas. Second, it increases the amount of antibodies produced in response to protein antigens by lengthening the antibody production time and allowing the B cells to become memory cells. When memory cells are present, any subsequent introduction of a previously injected antigen would stimulate a similar immune response. These actions are poorly observed when the antigen used is not made up of proteins.

Freund’s complete adjuvant is a very potent agent because it stimulates both cell-mediated and humoral immunity, which means that both antibodies and the immune system’s attack cells called thymus-derived cells (T cells) are mobilized to eradicate the antigens. The solution is a toxic agent because mineral oil cannot be efficiently metabolized. It can result in granuloma formation, necrosis, inflammation, induration, and pain at injection sites. Multiple exposure to complete adjuvant could lead to severe adverse reactions, decreased immunity, and even death.

When using Freund’s complete adjuvant, all materials should be sterile and injection sites should be thoroughly cleaned to prevent contamination and infection. The preferred route is subcutaneous or intraperitoneal. Other injection routes could lead to complications. Ulcers and necrosis may result from intradermal administration, death of muscles and lameness may result from intramuscular administration, and pulmonary embolism may result from intravenous administration.

Freund’s complete adjuvant is a hazardous substance and is not approved for tests on humans. It it harmful when both inhaled and swallowed, and can cause sensitization on skin contact. When handling this agent, protective clothing should be worn, and the handling area should be well lit and well ventilated.