Bovine neutrophils kill the sexually-transmitted parasite Tritrichomonas foetus using trogocytosis.

The protozoan parasite Tritrichomonas foetus (T. foetus) is the causative organism of bovine trichomonosis (also referred to as trichomoniasis), a sexually-transmitted infection that reduces fertility in cattle. Efforts to control trichomonosis on cattle farms are hindered by the discouragement of antibiotic use in agriculture, and the incomplete, short-lived protection conferred by the current vaccines. A more complete mechanistic understanding of what effective immunity to T. foetus entails could enable the development of more robust infection control strategies. While neutrophils, the primary responders to infection, are present in infected tissues and have been shown to kill the parasite in vitro, the mechanism they use for parasite killing has not been established. Here, we show that primary bovine neutrophils isolated from peripheral blood rapidly kill T. foetus in vitro in a dose-dependent manner, and that optimal parasite killing is reduced by inhibitors of trogocytosis. We also use imaging to show that bovine neutrophils surround T. foetus and trogocytose its membrane. These findings are consistent with killing via trogocytosis, a recently described novel neutrophil antimicrobial mechanism.

Two novel proteins, TtpB2 and TtpD2, are essential for iron transport in the TonB2 system of Vibrio vulnificus.

In gram-negative bacteria, energy-dependent active transport of iron-bound substrates across the outer membrane is achieved through the TonB systems of proteins. Three TonB systems have been identified in the human pathogen Vibrio vulnificus. The TonB1 system contains three proteins: TonB1, ExbB1, and ExbD1. Both the TonB2 and TonB3 systems have been shown to also contain a fourth protein, TtpC2 and TtpC3, respectively. Here, we report and begin to characterize two additional proteins in the TonB2 and TonB3 systems: TtpB and TtpD. Both TtpB2 and TtpD2 are absolutely required for the function of the TonB2 system in V. vulnificus. However, although both TtpB3 and TtpD3 in the TonB3 system are related to the proteins in the TonB2 system, neither are active in iron transport. All six protein components of the TonB2 system-TonB2, ExbB2, ExbD2, TtpB2, TtpC2, and TtpD2-are essential for the uptake of both endogenously produced iron-bound siderophores and exogenous siderophores produced from other organisms. Through complementation, we have shown that V. vulnificus is capable of using different TtpD2 proteins from other Vibrio species to bring in multiple siderophores. In contrast, we also demonstrate that TtpB2 must come from V. vulnificus, and not other species within the genus, to complement mutations in the TonB2 system.