Purification and characterization of a 45-kDa concealed antigen from the midgut membranes of Ornithodoros erraticus that induces lethal anti-tick immune responses in pigs.

Ornithodoros erraticus is an argasid tick that can transmit severe diseases such as human relapsing fever and African swine fever. In the search for a vaccine against this parasite, a crude extract of tick midgut membranes (GME) was obtained that in pigs and mice induced a protective response able to kill up to 80% of the nymphs in the first 72 h post-feeding and to reduce the fecundity of females by more than 50%. To identify the protective antigens, the GME was subjected to successive biochemical fractionations and the resulting simpler protein fractions were inoculated in pigs. A 45-kDa antigen, the so-called Oe45, was detected, purified and demonstrated to be responsible for the protection induced by the GME. Oe45 seems to be a membrane protein that is presumably expressed on the luminal membrane of midgut epithelial cells. Oe45 consists of at least two differently charged bands (cationic and neutral), which show antigenic cross-reactivity. The possibility that these bands might be different isoforms of the same protein is discussed. Although Oe45 is constitutively expressed at low levels throughout the trophogonic cycle, its expression is up-regulated by the ingestion of blood, as suggested by the higher levels observed between 6 and 72 h post-feeding.