Trypanosoma congolense: High erythropoietic potential in infected yearling cattle during the acute phase of the anemia

N'Dama (Bos taurus) cattle are known to tolerate trypanosome infections, developing less severe anemia and lower parasitemia, compared to Boran (Bos indicus) cattle. Young calves were also reported to be more resistant to trypanosomiasis than adult cattle. To expore the basis for this resistance, the erythropoietic response was evaluated in four naive yearling N'Dama calves and four age-matched Boran calves which developed anemia over a 140-day primary infection with Trypanosoma congolense clone IL 13E3. Similar levels of parasites were detected in the two breeds until 42 days postinfection (dpi). During the same period, a rapid and greater colony-forming units-erythroid response in the bone marrow of yearling Boran calves, compared with N'Dama calves, may explain the unusual absence of breed differences in mean packed cell volumes (PCV). However, this early erythropoietic response was transient and did not result in any rise in PCV in the Boran calves. Moreover, dispite the persistent severe anemia, the erythroid response subsided from 70 dpi onward. In contrast, in the N'Dama calves, following the erythroid response, the mean PCV was gradually compensated from 56 dpi onward and reached 30 percent by 126 dpi. This period of PCV recovery coincided with low and intermittent parasitemia and a return of the erythroid progenitor levels to near preinfection values. Elevated levels of erythroid progeniotrs in the N'Dama calves, occurring 1 week after trypanocidal treatment, returned the PCV to preinfection values. These results suggest that the age of the Bos indicus cattle has important impact on the early bone marrow response in primary T. congolense infection and confirmed previous suggestions of a high erythropoietic potential in trypanosome-infection and confirmed previous suggestions of a high erythropoietic potential in trypanosome-infected young calves

The effect of Trypanosoma brucei brucei infection on rabbit plasma iron and zinc concentrations

Changes in plasma iron and zinc concentration were studied in rabbits following a needle challenge with Trypanosoma brucei brucei clone ILTat 2.1. The infection resulted in a decrease of the concentration of both trace elements. Plasma iron concentrations decreased gradually and were decreased maximally to 53.3 percent of pre-infection levels on day 19 post-inoculation. Plasma zinc concentrations, on the other hand, decreased more rapidly and were decreased maximally to 27.4 percent of pre-infection levels on day 3 post-inoculation. The onset of these decreases coincided with the appearance of parasites in the peripheral blood. Furthermore, the magnitude of their decrease correlated closely with the level and duration of the parasitaemia. Other abnormal findings, namely, anaemia and periods of leucocytosis and leukopenia, were also observed. This study therefore demonstrates that depression in plasma iron and zinc concentrations is part of the acute phase response in rabbits infected with this clone of T.b brucei

The role of the bone marrow in bovine trypanotolerance. 1. Changes in blood and bone marrow in Trypanosoma congolense-infected cattle

This study compared the changes in the bone marrow (BM) of five trypanotolerant N'Dama cattle with those of four trypanosusceptible Boran cattle during trypanosome infection. In the early parasitaemic phase, from 12 to 21 days postinfection (DPI), tsetse transmitted primary Trypanosoma congolense IL 1180 infection induced parasitaemia, slight depression in packed cell volume (PCV), marked leucopenia due to lymphocytopenia and eosinopenia, and thrombocytopenia which were of similar intensity in Boran and N'Dama cattle. However, from 28 DPI until the end of the experiment on 112 DPI, the parasitaemia was higher in the Boran than in the N'Dama. Severe anaemia and leucopenia characterised by lymphopenia, neutropenia, eosinopenia and monocytopenia persisted in Boran cattle. In contrast, the PCV values dropped gradually in N'Dama cattle and from 77 DPI recovered slowly to values just below preinfection levels by 112 DPI. The total and differential leucocyte counts of the N'Dama cattle stabilised at approximately two thirds of preinfection values between 28 and 112 DPI, and were double those of the Boran. Marked thrombocytopenia occurred in both breeds. The anaemia was initially macrocytic hypochromic but terminally became microcytic hypochromic in both breeds. Light and electron microscopic studies of sequential biopsies of the BM of these animals showed that the BM response was the key to these differences between the N'Dama and Boran. The biopsies of the BM of the N'Dama cattle were hypercellular (scored 4.5 ± 1.0 compared to 4.0 for controls) with mild hyperplasia of erythroid cells and mild hypoplasia of myeloid cells from 28 to 112 DPI, endowing the animals with higher haemopoietic potential that enabled them to replace most lost cells. In contrast, the Boran cattle had hypocellular (scored 2.4 ± 1.1) BM biopsies with relative erythroid hyperplasia and myeloid hypoplasia, resulting in low capacity of cell replacement manifested as severe unremitting anaemia and leucopenia. The BM of both breeds showed moderate hyperplasia of cells of the mononuclear phagocyte system. Therefore, this study showed, for the first time, that BM response is a key determinant factor of trypanotolerance as it determines the animal's capability for blood cell regeneration

The haematology of Trypanosoma congolense infection in cattle. I. Sequential cytomorphological changes in the blood and bone marrow of Boran cattle

Five adult Boran cattle (Bos indicus), infected with a clone of Trypanosoma congolense IL13-E3 three years earlier and treated, were re-challenged with the same clone. Changes in the peripheral blood were monitored twice weekly, and events in the bone marrow (BM) were assessed by weekly biopsies of the sternal BM, until day 98 postinfection (dpi) when the three surviving animals were treated with diminazene aceturate. One animal died on 57 dpi whereas another was treated on 63 dpi when the packed cell volume was 15 percent. The infected animals developed anaemia, leucopenia and thrombocytopenia during the first peak of parasitaemia which persisted until the experiment was terminated. Three phases of BM response were demonstrated on light microscopic examination of BM smears. The first, the preparasitaemic phase represented by samples taken on 15 dpi, was an immunological response with slight but significant increases in lymphoblasts, lymphocytes, plasma cells and macrophages (Mo) whereas erythroid and granulocytic cells were unchanged. The second, the early parasitaemic or acute phase (21-57 dpi) associated with the development of anaemia, leucopenia and thrombocytopenia, was characterised by intensification of the immunological response, and an early but transient granulocytic hyperplasia. The third, the late parasitaemic or chronic phase (63-98 dpi) associated with persisting pancytopenia, was characterised by erythroid, megakaryocytic and Mo hyperplasia, dyserythropoiesis, granulocyte hypoplasia and return of lymphoid cell counts to preinfection numbers. Transmission electron microscopy confirmed these findings and showed that intact trypanosomes were not observed in the sinusoids and haemopoietic compartment of the BM. This study demonstrates that T. congolense infection affects haemopoiesis, downregulating or upregulating the various blood cell lineages depending on the stage of infection. This suggests a fine control mechanism, presumably cytokine-mediated. Erythropoiesis, thrombopoiesis and monocytopoiesis were generally upregulated, whereas granulopoiesis was downregulated. However, haemopoiesis was generally ineffective as numbers of circulating blood cells remained below preinfection levels throughout the period of the study

The role of the bone marrow in bovine trypanotolerance. II. Macrophage function in Trypanosoma congolense - infected cattle

Sequential biopsies of sternal bone marrow (BM) of three trypanosusceptible Boran and three trypanotolerant N'Dama cattle were examined by light and transmission electron microscopy before and up to 112 days postinfection (DPI) with Trypanosoma congolense. Before infection, the percentage of cells of the mononuclear phagocyte system (MPS) including the macrophage (MO) and the calculated index of Mo volume in the BM were similar in both breeds, whereas the mean Mo surface area was significantly higher (p<0.0001) in the Boran than in the N'Dama. During T. congolense infection, the MPS cell counts, the Mo surface area and the calculated Mo volume index increased significantly in both breeds particularly in the N'Dama. Macrophages phagocytosed only a few erythrocytes and mature neutrophils in both breeds before infection. During infection, Mo engulfed many erythrocytes, reticulocytes, normoblasts, granulocytes and their precursors, and thrombocytes, as well as few lymphocytes and monocytes. Many Mo phagocytosed cells from more than one cell lineage, and phagocytosis of nucleated cells was preceded by attraction of the target cell and subsequent adhesion to the MO, suggesting a common mechanism of cell destruction. The Mo of cattle maintained contact, through reciprocal U - or V-shaped microvilli or filiform processes, with haemopoietic cells. These contacts increased during the acute phase of T. congolense infection in both breeds and remained elevated in the N'Dama until 112 DPI, whereas they dropped to preinfection levels in the chronic phase (98, 112 DPI) in the Boran. Cumulatively, the absolute numbers, surface area, organelle contents and calculated volume index of the MO, percentage of Mo with phagocytosed cells, the total cells engulfed, adhesion of target cell to Mo prior to phagocytosis, phagocytosis of multiple cell lines, as well as the percentage of Mo in contact with haemopoietic cells, and the total haemopoietic cells in contact with Mo were significantly higher in the N'Dama than in the Boran. Cell phagocytosis and contact with haemopoietic cells decreased in Boran cattle during the chronic phase but remained elevated in the N'Dama. The positive balance between the beneficial effects of Mo activation in the BM (enhanced haematopoiesis, and presumably parasite clearance and antigen processing) and its deleterious effect (cytophagia) was greater in the trypanotolerant N'Dama than in the Boran, enabling the N'Dama to resist infection better. This study therefore demonstrates that superior BM responses, pivoted on vital Mo functions, play a major role in trypanotolerance

Bone marrow and macrophage functions as determinants of bovine trypanotolerance

Sequential changes in the blood and bone marrow (BM) were studied by light and transmission electron microscopy in three Boran and three Ndama cattle before and after a primary infection with Trypanosoma congolense IL 1180. Parasitaemia was essentially similar in the Borans and the Ndamas between day 11 post-infection (DPI) and 59 DPI. Thereafter, until 112 DPI when the study was terminated, parasitaemia was higher in the Boran than in the Ndama. During the acute phase, the infection induced anaemia and leucopaenia which were milder in the Ndama than in the Boran. In the chronic phase, the leucocyte numbers and PCV of the Ndama improved, approaching pre-infection levels, whereas the values for the Boran continued to drop. Moderate thrombocytopaenia developed in the two breeds of cattle with no remarkable differences between them. The cellularity of BM biopsies were similar in the two breeds before infection. Following infection, the BM biopsies of Ndama cattle were consistently hypercellular while those of the Boran were hypocellular. The infection caused marked erythroid hyperplasia with marked hypoplasia of granulocyte elements in the Boran while there were only moderate corresponding shifts in these cell lineages in the Ndama. There was moderate hyperplasia of macrophages (Mo) in the bone marrow of both breeds, and the calculated volume index of Mo was 19.5 (+ or -) 3.6 in the Boran and 33.2 (+ or -) 3.9 in the Ndama (D<0.005) compared to 5.3 (+ or -) 1.4 and 4.7 (+ or -) 0.6 respectively, before infection. The Mo of both breeds were activated as shown by their significantly increased sizes and organelle (mitochondria, ER) contents, but those of the Ndama were more activated. The Mo in the BM phagocytosed immature and mature haemopoietic cells in the BM pariticulary erythrocytes, granulocytes and thrombocytes and smaller numbers of lymphoid cells and monocytes. Cells phagocytosis was preceded by cell to Mo attraction, and then adhesion. Prior to infection, the Mo had contacts with haemopoietic cells through V- or U-shaped microvilli apparently associated with Mo control of haemopoiesis; these contacts increased during infection. Target cell adhesion to Mo and phagocytosis, and contacts with haemopoietic cells were more marked with Mo of the Ndama than in the Boran, and these activities were further reduced in the boran on 98 and 112 DPI. In conclusion, it would appear that the Ndama achieve this superior tolerance because of hypercellularity of the BM and the greater activation of the Mo which result in greater haemopoiesis. Since cytophagia was also greater in the Ndama, our results indicate that this breed produces more blood cells and destroys more than the Boran. The balance between production and destruction appears to be much greater in the Ndama than in the Boran. The results of this study show that the BM is the key determinant organ of trypanotolerance in cattle while the Mo, particularly those of the BM, form the pivot of this control

The haematology of Trypanosoma congolense infection in cattle. II. Macrophage structure and function in the bone marrow of Boran cattle

Macrophages (Mo) in smears and sections of sternal bone marrow (BM) derived by weekly sequential biopsies from five adult Boran cattle re-challenged with Trypanosoma congolense were studied by light and transmission electron microscopy (TEM). Cells of the mononuclear phagocyte system including monoblasts, promonocytes, monocytes and Mo increased several fold in the sinusoids and haemopoietic compartment (HC) of the BM during infection. Mo activation occurred with significant increases (p<0.001) in Mo size and numbers of organelles including mitochondria, lysosomes and rough endoplasmic reticulum. Light microscopic examination of the BM smears showed that 25.8 percent of 1200 Mo examined phagocytosed many non-mitotic harmopoietic cells of the erythroid and granulocytic series as well as mature erythrocytes and thrombocytes but seldom lymphocytes from day 29 postinfection (dpi), when the first peak of parasitaemia occurred, until and termination of the experiment on 98 dpi. Some of the Mo with phagocytosed cells (10.4 percent) had cells from more than one lineage. TEM confirmed cytophagia and showed that the process begins with cell to Mo attraction characterised by development of microvilli at the surface of contact by the target cell and of envoloping pseudopodia by the Mo. This was followed by target cell to Mo adhesion and finally phagocytosis. The cells being phagocytosed and those freshly engulfed appeared morphologically normal. Many Mo were heavily laden with haemosiderin in the chronic phase of the infection (78 and 98 dpti). TEM showed that the activated Mo in the BM developed extensive contacts through reciprocal blunt microvilli with the haemopoietic cells. Macrophages were absent from the sinusoids of the BM prior to infection but became numerous during infection, and were adhered to sinusoidal endothelial cells by reciprocal blunt microvilli. These Mo phagocytosed blood cells (erythrocytes, neutrophils, thrombocytes), and free trypanosomes which, though present in the arterioles of the BM, were never seen in the sinusoids and HC of the BM. This study indicates that the Mo plays very vital roles in regulating and executing the events in the BM during T. congolense infection of cattle