The endogenous cannabinoid 2-arachidonoyl glycerol as in vivo chemoattractant for dendritic cells and adjuvant for Th1 response to a soluble protein

The decision-making mechanisms that determine the choice of the appropriate effector immune response to a microbial challenge are poorly understood. The endocannabinoid 2-arachidonoylglycerol (2-AG), injected intradermally in mice together with a soluble protein and a T helper-2 (Th2) priming Toll-like receptors (TLRs) agonist during primary immunization, shifts the memory response to the Th1 type. This effect can be shown by the enhanced hypersensitivity response and by the Th1 pattern of cytokines production that was abolished by the specific cannabinoid receptor CB2 antagonist SR 144528. 2-AG seems to operate during the innate response by increasing the number of dendritic cells (DCs) migrating to the draining lymph nodes. Expression of CB2 mRNA but not of the protein was higher in immature vs. mature DCs. Consistently, in vitro, 2-AG exerted a potent chemotactic activity on both immature and mature DCs. In conclusion, we suggest that, in vivo, the endocannabinoid 2-AG may act as chemotactic substance capable of recruiting DCs and/or their precursors during the innate immune response that, in presence of a TLR agonist, consequently instruct a Th1-shifted adaptive response. As 2-AG may be induced in tissues by various stimuli at concentrations similar to that used in our study, this evidence might be of a wide-ranging pathophysiological relevance.