INVESTIGATION INTO THE ROLE OF SIALIDASE-INDUCED GALACTOSE EXPOSURE IN THE ERYTHROPHAGOCYTOSIS OF BOVINE TRYPANOSOMIASIS

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Date
2000-05
Authors
OMAGE, JEBBA JAMES
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Abstract
The mechanism that mediate recognition and subsequent sequestration of erythrocytes during bovine trypanosomiasis in Trypanosoma vivax infected calves with and without lactose infusion was investigated. Sialidase induced exposure of carbohydrate on erythrocytes following removal of sialic acid with increasing parasitemia, were examined using an in vitro cell binding assay that allows spontaneous formation of cell contacts. The results obtained indicate a preferential recognition of erythrocytes taken from the T. vivax infected animals, as compared to those from non-infected animals by rat peritoneal macrophages. This recognition manifested itself by adhesion of the complementary cells in the form of rosettes and hence could explain partly the removal of erythrocytes from circulation during bovine trypanosomiasis. Adhesion was shown by inhibition studies with monosaccharides and oligosaccharides. The inhibition pattern of D-galactosc > Lactose > Maltose > D-glucose > Mannosc was observed. freshly isolated rat peritoneal macrophages in vitro strongly bound desialylated erythrocytes of calves infected with Trypanosoma vivax. A consistently higher level of binding was observed in the lactose infused infected calves adduced to a consistent presence of the trypanosome parasite in the peripheral circulation of the lactose - infused calves. A concomittant higher level of free serum sialic acid concentrations was also observed in the lactose-infused infected calves throughout the experimental period. Correlation studies showed a strong positive association (P<0.001) between serum sialic acid and rosette formation. An initial but non-significant (P>0.05) increase in free serum sialic acid concentration was observed in both infected groups of calves and this coincided with increased parasitemia. The initial increase coincided with increased rosette formation and increased parasitaemia. Parasitaemia in both groups of infected calves continued to rise after the establishment of patent infection and peaked 5 days alter infection. While trypanosomes flourished in numbers large enough to be counted throughout the period of the study in the infected calves that were injected with lactose, they were too scanty to be counted by day 8 alter infection in the infected calves that were not injected with lactose. These observations demonstrate that phagocytosis of erythrocytes early in bovine trypanosomiasis may partly be due to the cleavage of sialic acid, exposure of p-galactosc residues and binding of the erythrocyte by perhaps p-galactose specific lectin on the host macrophages. The persistent parasitaemia, higher concentrations of free serum sialic acids and higher binding and resetting observed in the lactose infused infected calves strongly suggest more desialylation of the erythrocytes, inspite of the lactose infusion.
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A Thesis submitted to the Postgraduate School, Ahmadu Bello University, Zaria, in partial fulfillment of the requirements for the award of the Degree of Doctor of Philosophy (Ph.D.) Department of Biochemistry, Faculty of Science, Ahmadu Bello University, Zaria. MAY, 2000
Keywords
INVESTIGATION,, ROLE,, SIALIDASE-INDUCED,, GALACTOSE,, EXPOSURE,, ERYTHROPHAGOCYTOSIS,, BOVINE,, TRYPANOSOMIASIS.
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