The accumulative amount of aluminium during typical long-course SCIT is summarised in Table 2. Upon subcutaneous injection, a local reaction forms once the antigen-adjuvant preparation comes into contact with the interstitial fluid (tissue space) and plasma. The majority of the adjuvant will remain in this vicinity for a number of hours, if not days. Dissolution of particulate aluminium will then occur, partly driven through a solubility/pH gradient. As more Al3+(aq) evolves it then becomes Ivacaftor nmr available for binding by soluble ligands (e.g. transferrin and other proteins or ligands), thus accelerating the dissolution process [46]. The in vivo clearing of aluminium adjuvants has been studied in some

detail using a radioactive isotope of aluminium (26Al) administered in rabbits [63]. Mass spectrometry monitored the fate of the administered isotope for a period of 28 days.

Approximately 1 h after injection, aluminium could be detected in the blood and remained steady for 28 days, however represented only a small fraction of the total aluminium dose administered. Urine samples monitored a 6% cumulative amount of aluminium eliminated in urine after 28 days, which was still being excreted. It must be stressed that neither such test will provide an accurate indication of the total systemic aluminium body burden of an individual and where it can be found in the body. However, in the GSK1210151A same study the concentration of aluminium was approximately three times greater in tissues with the following distribution pattern: kidney > spleen > liver > heart > lymph node > brain. As described in Exley [59], “A single injection also of 1 mg of aluminium adjuvant will add 1 mg of aluminium to the body burden but this milligram of aluminium will distribute throughout the body according to myriad different influences beginning with those occurring at the injection site”. While aluminium is released from the injection

site and can be excreted, it clearly has the propensity to form small focal accumulations in body tissues (including the brain) which can arise and slowly build over the life-time of an individual. The efficacy of aluminium compounds as adjuvants is undisputed, and similarly to vaccines they have been reportedly used in SCIT since 1937 [52]. The current guideline of German Allergy Societies classifies aluminium compounds as depot mediators [55]. Other commercial depot mediators used in SCIT are calcium phosphate and l-tyrosine. Although the gradual release explanation is inadequate to explain aluminium’s adjuvant potential, the physical adsorption of antigen onto the adjuvant is still considered to be a very important mechanism. Particularly in SCIT where slower release of allergens from the injection site (thereby increasing the duration of antigen presentation) is pivotal in improving tolerability of the allergens [64].