Identification of three members of the multidomain adhesion CCp family in Babesia gibsoni.

Babesia gibsoni is an intraerythrocytic apicomplexan parasite transmitted by Haemaphysalis longicornis and causes canine babesiosis. Within the tick, the Babesia parasite undergoes sexual conjugation and the sporogony process of its life cycle. To control B. gibsoni infection, prompt and effective treatment of acute infections and curing chronic carriers are urgently needed. Gene disruption of Plasmodium CCps resulted in blocking the transition of sporozoites from the mosquito midgut to the salivary glands, showing that these proteins are potential targets for the development of a transmission-blocking vaccine. In this study, we described the identification and characterization of three members of the CCp family in B. gibsoni, named CCp1, CCp2, and CCp3. The B. gibsoni sexual stages were induced in vitro by exposing parasites to xanthurenic acid (XA), dithiothreitol (DTT), and tris (2-carboxyethyl) phosphine (TCEP) at serial concentrations. Among them, 100 µM XA-exposed and cultured at 27 °C without CO2 B. gibsoni presented diverse morphologies, including parasites with long projections, gradually increased free merozoites, and aggregated and round forms, indicative of sexual stage induction. Then, the expression of CCp proteins of induced parasites was confirmed by real-time reverse transcription PCR, immunofluorescence, and western blot. The results showed that BgCCp genes were highly significantly increased at 24 h post-sexual stage induction (p < 0.01). The induced parasites were recognized by anti-CCp mouse antisera and anti-CCp 1, 2, and 3 antibodies weakly reacted with sexual stage proteins of expected molecular weights of 179.4, 169.8, and 140.0 KDa, respectively. Our observations on morphological changes and confirmation of sexual stage protein expression will advance elemental biological research and lay the foundation for the development of transmission-blocking vaccines against canine babesiosis.