Bacterial toxins: potential weapons against HIV infection.

Natural toxins are the product of a long-term evolution, and have captured crucial events in the most essential and vital processes of living organisms. They can attack components of the protein synthesis machinery (as in the case of Diphteria and Shiga toxins, and Ribosome inactivating proteins), actin polymerization (Clostridium botulinum type C, C2, toxins and Enterotoxin A), signal transduction pathways (Cholera toxin, Heat-labile enterotoxins, Pertussis and Adenylate cyclase toxins), intracellular trafficking of vesicules (for Tetanus and Botulinum neurotoxin type C) as well as immune and/or inflammatory responses (Pyrogenic exotoxins, Cholera and Pertussis toxins). Of interest is the fact that several bacterial and vegetal toxins can either kill selectively cells infected with the human immunodeficiency virus (HIV) or exert inhibitory effects on its life cycle. In particular both pertussis toxin (PTX) and its nontoxic B-oligomeric component (PTX-B) can block the infectious process in vitro at multiple levels, by preventing the entry of CCR5-dependent (R5) HIV strains and by inhibiting both R5 and CXCR4-dependent HIVs at post-entry level(s). In addition, some toxins possess immunostimulating properties that have been exploited in terms of adjuvancy and induction of specific cytotoxic T lymphocytes responses to different vaccine preparations, including some experimental vaccine against HIV infection. Thus, toxins may represent a relatively unexplored exhibition of powerful biological agents that could either prevent infection or attack HIV-infected cells.