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. Author manuscript; available in PMC: 2010 Dec 9.
Published in final edited form as: Immunol Lett. 2009 Nov 4;128(1):29–35. doi: 10.1016/j.imlet.2009.10.005

Fig. 1.

Fig. 1

Mechanisms of adjuvants. The initiation of Th cell responses requires three signals, referred to as signal 0, signal 1 and signal 2. In theory, adjuvants can act on each of these three signals. Most of the recently developed specific adjuvants, such as Toll-like receptor (TLR) agonists, are called type A adjuvants (e.g. MPL). Adjuvants and formulations targeting antigen processing cells (APCs) or favoring antigen capture are called type B adjuvants (e.g. aluminum hydroxide), acting on signal 1, as their effect is mediated by enhanced antigen presentation to T cells. Specific ligands of co-stimulatory molecules, like the CD28 agonist TGN1412, can enhance signal 2 and are called type C adjuvants. Signal 3 represents mediators delivered from the APC to the T cell, e.g. the cytokine IL-12.