Adjuvants: Effect and Example | Immunology

In this article we will discuss about the effect and examples of adjuvants.

Adjuvants (from Latin adjuvare, to help) are substances that, when mixed with an antigen and injected with it, enhance the immunogenicity of that antigen. Adjuvants are often used to boost the immune response when an antigen has low immunogenicity or when only small amounts of an antigen are available, limiting the immunizing dosage.

As for example, the antibody response in mice following immunization with BSA can be increased five fold or more if the BSA is adminis­tered with an adjuvant.

Effect of Adjuvants:

Though augmentation of adjuvants in the immune response is not completely known but they exert several effects like:

(a) Help to prolong antigen persistence;

(b) Help to enhance co-stimulatory formation;

(c) Help to induce granuloma formation and

(d) Help to stimulate typhocyte proliferation non-specifically.

Examples of Adjuvants:

i. Aluminum-potassium sulfate (alum)

ii. Freund’s incomplete adjuvant

iii. Freund’s complete adjuvant

i. Aluminum-potassium sulfate (alum):

This alum acts to increase antigen persistence. When an antigen is mixed with alum, the salt precipitates the antigen. Injection of this alum precipitate, results in a slower release of antigen from the injection site, so that the effective time of exposure to the antigen increases from a few days (without adjuvant) to several weeks (with the adjuvants). The alum precipitate also increases the size of the antigen and thus increasing the likeli­hood of phagocytosis.

ii. Freund’s incomplete adjuvant:

Freund’s water in oil adjuvants prolong the persistence of antigens. It contains antigen in aqueous solution, mineral oil, and an emulsifying agent such as mannide monosoleate which dis­perses the oil into small droplets surrounding the antigen. The antigen is then released very slowly from the site of injection.

iii. Freund’s complete adjuvant:

This contains heat-killed Mycobacteria in the water in oil emulsion. A muramul dipeptide component of the mycobacterial cell wall acti­vates macrophages, making Freund’s complete adjuvant more potent than the incomplete one.