INCREASE IN CD5(-CELLS AND DEPRESSION OF IMMUNE-RESPONSES IN SHEEP INFECTED WITH TRYPANOSOMA-EVANSI() B)

The effects of Trypanosoma evansi on the cellular and humoral immune r esponses of sheep to Pasteurella haemolytica vaccine were studied. Per ipheral blood lymphocytes (PBLs) from the sheep were analysed using si ngle and double-colour indirect immunofluorescence staining and flow c ytometry to monitor changes in circulating B and T cell subsets. Serum antibody responses were assayed using the enzyme-linked immunosorbent assay technique (ELISA), in addition to measuring local skin reaction s at the site of vaccine administration. Results showed significant in creases in circulating B cells in all sheep after the primary(p < 0.01 ) and secondary(p < 0.001) vaccinations although the increases were mu ch more dramatic in the T. evansi-infected sheep. In addition, infecti on induced significant increases (p < 0.004) both in proportions and n umbers of CD5(+) B cells with more than 70% of circulating B cells exp ressing the CD5 antigen and showed significant differences (p < 0.01) from those of control sheep in which vaccination alone failed to induc e similar increases. Also, infection resulted in significant decreases in CD5(+) (p < 0.003), CD4(+) (p < 0.03) and CD8(+) (p < 0.03)T cell subsets in contrast to their increases in all control animals after va ccination. Moreover, there were significant suppression of both local skin reaction (p < 0.005) and serum Ig and IgG(1) (p < 0.001) antibody responses to the vaccine antigen. (C) 1998 Published by Elsevier Scie nce B.V. All rights reserved.