An in vitro assay that measures the generation of superoxide anions (O₂ˉ) was used to assess the level of oxidative burst of phorbol myristate acetate (PMA) - and trypanosome-stimulated neutrophils isolated from healthy Boran and N'Dama cattle, and those infected with Trypanosoma congolense. PMA stimulation of healthy bovine neutrophils resulted in between 300-400% increase in O₂ˉ generation. Neutrophils of Boran cattle exhibited slightly higher, but insignificant O₂ˉ generation capacity than those of the N'Dama breed. In vitro stimulation by trypanosomes of neutrophils isolated from Trypanosoma congolense-infected cattle caused significant increases in O₂ˉ generation, especially on days 14, 28 and 42 post-infection, of both breeds of cattle. No significant differences were observed in O₂ˉ generation capacity of the neutrophils of both breeds of infected cattle throughout the period of assay. The results of this study have shown that PMA and trypanosomes do cause an enhanced in vitro oxidative burst, hence trypanosome phagocytosis and killing activity of neutrophils. Neutrophils have been shown to play very significant roles in parasite clearance, hence reduction of trypanosome parasitaemia. The rates of both in vitro generation of O₂ˉ and trypanosome phagocytosis over time did not differ significantly between Boran and N'Dama breeds of cattle, even during T. congolense infection in this study. Hence, it may be inferred that sustained and higher parasitaemia, more pronounced neutropenia, inadequate bone marrow response and less effective trypanosome-specific immune response, rather than defective neutrophil trypanosome destruction, may be the problem of trypanosusceptible cattle breeds.
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