TRYPANOSOMA-CONGOLENSE - COMPARATIVE EFFECTS OF A PRIMARY INFECTION ON BONE-MARROW PROGENITOR CELLS FROM NDAMA AND BORAN CATTLE

Using in vitro clonogenic assays, the changes in haemopoietic progenit or cell levels were compared in the bone marrow of three adult trypano tolerant N'Dama cattle and three age-matched trypanosusceptible Boran cattle over 17 weeks (119 days) of a primary Trypanosoma congolense (c lone IL 1180) infection. As the infection progressed, a clear tendency of the parasitaemia to decrease was seen in the N'Damas, while it rem ained high throughout the infection in the Borans. The decline in the colony-forming units-granulocyte macrophage (CFU-GM) between 7 and 42 days postinfection (dpi) corresponded with the decreased numbers of ne utrophils and monocytes in the blood observed in both breeds. Thereaft er, a further significant drop in the CFU-GM levels was observed in th e Borans which may partially explain the continued decrease in the num bers of neutrophils and monocytes in blood. In contrast, a significant peak of CFU-GM above preinfection levels was observed in the N'Damas on 49 dpi, which could partially explain the subsequent recovery of th e numbers of neutrophils and monocytes in blood. When compared to the N'Damas, the Borans had a more dramatic drop in the packed cell volume (PCV) from 25 dpi onwards, resulting in significantly lower PCV. From 46-49 dpi onwards, the mean PCV stabilised at significantly lower lev els in the Borans than in the N'Damas. The mean corpuscular volume (MC V) levels increased in both breeds, but at a much faster rate in the B orans. The clonegenic assays demonstrated an erythropoietic response, characterised by peaks above preinfection levels of both the early and late erythroid progenitor cells (respectively, burst-forming units-er ythroid, BFU-E, and colony-forming units-erythroid, CFU-E), occurring between 35 and 70 dpi in both breeds of cattle. However, despite a mor e severe anaemia in the Borans, the magnitude of their erythroid respo nse was similar to that of the N'Damas, suggesting that the response o f the Borans was insufficient to compensate for the greater degree of anaemia. Moreover, the mean PCV did not improve in the Borans, indicat ing the ineffectiveness of their erythropoietic response. An increased rate of erythrocyte destruction and/or a defective differentiation an d maturation of erythroid precursors have also been shown to be partia lly responsible for this persistent anaemia. From 98 dpi onwards, desp ite the persistent low PCV, the MCV decreased to preinfection levels a nd low CFU-E numbers were observed in the Borans. Over the same period , in the N'Damas the mean PCV progressively increased to reach 25%, wh ich fell within the low normal range for cattle. This may partially ex plain the return of the BFU-E to preinfection levels and the slight de crease in the CFU-E in the N'Damas. During the acute phase of a T. con golense infection, both the granulomonocytic and erythroid progenitors were increased more effectively in the N'Dama cattle than in the Bora n cattle, when compared to the degree of cytopaenia in blood; this mig ht correlate with the superior ability of the N'Damas to maintain high er numbers of granulocytes, monocytes, and erythrocytes in blood. (C) 1995 Academic Press, Inc.