title: Anti-VSG antibodies induce an increase in Trypanosoma evansi intracellular Ca2+ concentration.
abstract: Trypanosoma evansi and Trypanosoma vivax have shown a very high immunological cross-reactivity. Anti-T. vivax antibodies were used to monitor changes in the T. evansi intracellular Ca2+ concentration ([Ca2+]i) by fluorometric ratio imaging from single parasites. A short-time exposure of T. evansi parasites to sera from T. vivax-infected bovines induced an increase in [Ca2+]i, which generated their complete lysis. The parasite [Ca2+]i boost was reduced but not eliminated in the absence of extracellular Ca2+ or following serum decomplementation. Decomplemented anti-T. evansi VSG antibodies also produced an increase in the parasite [Ca2+]i, in the presence of extracellular Ca2+. Furthermore, this Ca2+ signal was reduced following blockage with Ni2+ or in the absence of extracellular Ca2+, suggesting that this response was a combination of an influx of Ca2+ throughout membrane channels and a release of this ion from intracellular stores. The observed Ca2+ signal was specific since (i) it was completely eliminated following pre-incubation of the anti-VSG antibodies with the purified soluble VSG, and (ii) affinity-purified anti-VSG antibodies also generated an increase in [Ca2+]i by measurements on single cells or parasite populations. We also showed that an increase of the T. evansi [Ca2+]i by the calcium A-23187 ionophore led to VSG release from the parasite surface. In addition, in vivo immunofluorescence labelling revealed that anti-VSG antibodies induced the formation of raft patches of VSG on the parasite surface. This is the first study to identify a ligand that is coupled to calcium flux in salivarian trypanosomes.
authors.affiliation: Centro de Estudios Biomédicos y Veterinarios, Universidad Nacional Experimental Simón Rodríguez, Caracas, Venezuela. memendoza@cantv.net
authors.forename: M
authors.initials: M
authors.lastname: Mendoza
authors.forename: G L
authors.initials: GL
authors.lastname: Uzcanga
authors.forename: R
authors.initials: R
authors.lastname: Pacheco
authors.forename: H
authors.initials: H
authors.lastname: Rojas
authors.forename: L M
authors.initials: LM
authors.lastname: Carrasquel
authors.forename: Y
authors.initials: Y
authors.lastname: García-Marchan
authors.forename: X
authors.initials: X
authors.lastname: Serrano-Martín
authors.forename: G
authors.initials: G
authors.lastname: Benaím
authors.forename: J
authors.initials: J
authors.lastname: Bubis
authors.forename: A
authors.initials: A
authors.lastname: Mijares