Aluminium salts are added as adjuvants to several inactivated vaccines including DTP, Tdap and hepatitis B. The principal immunological basis of alum adjuvant action is:

• A Direct activation of cytotoxic CD8 T cells through cross-presentation
• B Formation of an antigen depot with slow release and enhanced uptake by antigen presenting cells, favouring antibody responses ✓
• C Replication of the antigen within dendritic cells, mimicking a live infection
• D Induction of a predominantly Th1 response through toll-like receptor 9 signalling

Explanation

Alum acts by adsorbing the antigen, creating a depot that prolongs exposure, and by activating the NLRP3 inflammasome and enhancing phagocytic uptake, which skews responses toward Th2 and strong humoral immunity. It does not promote CD8 cytotoxic responses, which is why alum-adjuvanted vaccines are poor inducers of cell-mediated immunity. Option D describes CpG-type adjuvants acting through TLR9, and option C is impossible because alum carries no replicating material.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.