Snake presynaptic phospholipase A2 neurotoxins (SPANs) paralyze the neuromuscular junction (NMJ). Upon intoxication, the NMJ enlarges and has a reduced content of synaptic vesicles, and primary neuronal cultures show synaptic swelling with surface exposure of the lumenal domain of the synaptic vesicle protein synaptotagmin I. Concomitantly, these neurotoxins induce exocytosis of neurotransmitters. We found that an equimolar mixture of lysophospholipids and fatty acids closely mimics all of the biological effects of SPANs. These results draw attention to the possible role of local lipid changes in synaptic vesicle release and provide new tools for the study of exocytosis.

Vaccines are the most effective agents to control infections. In addition to the pathogen antigens, vaccines contain adjuvants that are used to enhance protective immune responses. However, the molecular mechanism of action of most adjuvants is ill-known, and a better understanding of adjuvanticity is needed to develop improved adjuvants based on molecular targets that further enhance vaccine efficacy. This is particularly important for tuberculosis, malaria, AIDS, and other diseases for which protective vaccines do not exist. Release of endogenous danger signals has been linked to adjuvanticity; however, the role of extracellular ATP during vaccination has never been explored. Here, we tested whether ATP release is involved in the immune boosting effect of four common adjuvants: aluminum hydroxide, calcium phosphate, incomplete Freund's adjuvant, and the oil-in-water emulsion MF59. We found that intramuscular injection is always associated with a weak transient release of ATP, which was greatly enhanced by the presence of MF59 but not by all other adjuvants tested. Local injection of apyrase, an ATP-hydrolyzing enzyme, inhibited cell recruitment in the muscle induced by MF59 but not by alum or incomplete Freund's adjuvant. In addition, apyrase strongly inhibited influenza-specific T-cell responses and hemagglutination inhibition titers in response to an MF59-adjuvanted trivalent influenza vaccine. These data demonstrate that a transient ATP release is required for innate and adaptive immune responses induced by MF59 and link extracellular ATP with an enhanced response to vaccination.vaccine adjuvants | danger associated molecular pattern | DAMP | inflammation V accine adjuvants are used to enhance immune responses toward coadministered antigens, thereby improving vaccine potency, immunological memory, or cross-protection (1, 2). Experimental adjuvants range from simple molecules such as calcium phosphate (CaPi) to very complex mixtures such as incomplete Freund's adjuvant (IFA), made of a water-in-oil emulsion, or complete Freund's adjuvant, which also includes killed Mycobacteria (3). However, for human vaccines, adjuvants of highly defined properties that combine efficacy with complete safety are needed; to date, very few compounds have been licensed. Some of the safest and most efficient adjuvants licensed for human use, such as aluminum hydroxide (alum) and the oil-in-water squalene-based emulsion MF59, have been empirically identified, and their mechanism of action is still not fully understood (4, 5). A better understanding of their mechanism of action is needed to develop improved adjuvants that further enhance vaccine efficacy. This is particularly important for diseases for which protective vaccines do not exist (6).An examination of the chemical nature of four major vaccine adjuvants (alum, CaPi, IFA, and MF59) suggested they could interact with the phospholipid bilayer of cell membranes via hydrogen bonding or ionic interactions with the head groups of phospholipids/glycolipids and/or via hydrophobic...