Chemical and Immunological Characteristics of Aluminum-Based, Oil-Water Emulsion, and Bacterial-Origin Adjuvants

Figure 1

Three-dimensional representation of adjuvants. (a) Crystal structures of aluminum salts used as adjuvants in human vaccines. Al(OH)₃ is the most widely used adjuvant in some crystal structures (such as gibbsite) and amorphous forms [86]. Another aluminum salt used in vaccines is aluminum oxide hydroxide such as goethite [87]. (b) Several bacterial membrane proteins are used as adjuvants in order to activate human immune cells. Bacterial flagellin is detected by TLR5 in innate cells activating a high immune response; recently, the B. subtilis flagellin structure was solved using cryomicroscopy under the 5WJT PDB code [88]. On the other hand, phospholipids and lipidic components in the bacterial membrane are recognized as dangerous and activate immune response. (c) The most used adjuvant in animal immunization is an emulsion of oil, paraffin, and M. tuberculosis death cells. (d) Squalene is an oil compound present in the liver of sharks as a precursor of cholesterol metabolism. In recent years, squalene has been accepted as an adjuvant for human vaccination. Immunological results of squalene have demonstrated it to be an efficient adjuvant. The coordinates of squalene were taken from the ZINC15 data bank [89].

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