Immune responses in pregnant cattle and bovine fetuses following experimental infection with Neospora caninum

Humoral and cell-mediated immune (CMI) responses [i.e. proliferative responses and gamma interferon (IFN-gamma) production], were elicited in five cows infected between 159 and 169 days of gestation by a combined intravenous-intramuscular inoculation of Neospora caninum tachyzoites. Analysis of antigen-specific immunoglobulin (IgG) subclasses revealed a predominant IgG2 response in two cows, a mixed IgG1-IgG2 response in two other cows and a predominant IgG1 response in one cow. No correlation was found between IgG2 titers and IFN-gamma levels. CD4-T cells were responsible for the CMI responses in peripheral blood mononuclear cells from three infected cows. All five fetuses removed from infected dams at week 9 post-infection (219-231 days of gestation) mounted strong Neospora-specific humoral responses and had a predominant IgG1 response, regardless of their ability to produce IFN-gamma. However, CMI responses were highly variable between fetuses. These data indicate the complexity of the immune mechanisms associated with Neospora infection in both the dams and their fetuses.

A POLYGEN-adjuvanted killed Neospora caninum tachyzoite preparation failed to prevent foetal infection in pregnant cattle following i.v./i.m. experimental tachyzoite challenge

Cattle immunised with a POLYGEN-adjuvanted killed Neospora caninum tachyzoite preparation were previously shown to produce interferon (IFN)-gamma at levels similar to those of tachyzoite-infected cattle. In view of the critical role of IFN-gamma in resistance of mice to N. caninum infection, these results prompted us to test the POLYGEN-adjuvanted preparation in pregnant cattle to determine whether it will be able to prevent foetal infection following an experimental tachyzoite challenge. Seven heifers were immunised at 35 and 63 days of gestation with the POLYGEN-adjuvanted preparation, while five heifers were inoculated with POLYGEN alone at the same days of gestation. Four weeks later, all heifers were challenged with a combined i.v./i.m. inoculation of tachyzoites. The same challenge was given to seven unimmunized heifers at the same stage of gestation. An additional unimmunized heifer was inoculated with uninfected monolayer cell culture material. All challenged heifers, immunized and unimmunized, had infected foetuses. Immunized heifers developed both parasite-specific humoral and cellular immune responses, characterised by increased IFAT titres, a predominant IgG1 response, elevated lymphoproliferative response and IFN-gamma production. Following tachyzoite challenge, they developed an anamnestic humoral response and produced similar amounts of IgG1 and IgG2 antibodies, but did not have an anamnestic cellular immune response. The lack of anamnestic cellular immune response and/or the large i.v/i.m tachyzoite inoculum may have contributed to the failure of the preparation.

Neosporosis in cattle

During the past decade, Neospora caninum infection has emerged as an important reproductive disease in cattle throughout the world. Abortion, occurring during the middle of gestation, is the primary clinical sign of the infection in cattle. Surveys in several countries from three continents have identified N. caninum infection as the major diagnosed cause of bovine abortion. Both endemic and epidemic patterns of abortion may occur in herds. An important feature of this disease is that the protozoan parasite is maintained in cattle as a chronic infection which can be passed on to the fetus during pregnancy. Two methods for the transmission of the infection in cattle have been proposed and are the subject of current investigations. Horizontal transmission utilizes a two-host life cycle whereby the cow is infected from ingestion of coccidial oocyst stages shed by the definitive host. Experimental infections have confirmed that the dog is a definitive host for the parasite. There is epidemiological evidence that the dog has a role in the prevalence of the infection but, as yet, no confirmation that the dog is the source for natural infections in cattle. Vertical transplacental transmission of the infection is an important route of infection in many herds. Vertical transmission occurs because fetal infection frequently does not result in abortion but rather the fetus survives to be a persistently infected animal. A heifer calf that is born congenitally infected is capable of transmitting the infection to the next generation when she becomes pregnant, thus maintaining the infection in the herd. The clinical outcome of transplacental fetal infection with N. caninum is likely determined by maternal and fetal immune responses which involve humoral, and most importantly, cell-mediated immune factors. The diagnosis of the infection is assisted through histopathology and immunohistochemical examination of aborted fetuses and serologic testing of cattle for evidence of infection. Several types of serologic tests, based on the use of culture-derived organisms or recombinant N. caninum antigens are available. There are no proven control methods for the prevention or treatment of neosporosis. Suggested control measures focus on programs to reduce the number of congenitally infected animals retained in the herd and to minimize the opportunity for postnatal transmission from the environment.

Immunogenicity of a killed whole Neospora caninum tachyzoite preparation formulated with different adjuvants

A killed whole Neospora caninum tachyzoite preparation was formulated with various adjuvants and tested for its immunogenicity in cattle. The adjuvants used were: Havlogen, a polymer of acrylic acid cross-linked with polyallylsucrose; Polygen, a non-particulate copolymer; a mixture of Havlogen and Bay R-1005, which is a preparation of free base synthetic glycolipids; and Montanide ISA 773, a water-in-oil emulsion made with a mixture of metabolisable and mineral oils. Immune responses in immunised cattle were compared with those of cattle experimentally infected with culture-derived N. caninum tachyzoites. The overall mean serum IFAT titres were significantly higher (P < 0.05) in experimentally infected cattle compared with all immunised cattle. Nonetheless, the maximum antibody titres of the immunised cattle, which were obtained following the third immunisation, were within the range of titres previously described for naturally infected cattle. The overall mean serum IFAT titres were significantly higher (P < 0.05) in cattle immunised with the killed tachyzoite preparation formulated with Polygen and with the mixture of Havlogen and Bay R-1005, compared with cattle immunised with the Havlogen- and Montanide-based preparations. Two of the four adjuvant preparations were able to induce cell-mediated immune responses similar to those of the experimentally infected cattle. The Havlogen-adjuvanted tachyzoite preparation elicited N. caninum-specific proliferation of peripheral blood mononuclear cells statistically similar (P = 0.095) to that of the infected animals. Peripheral blood mononuclear cells from animals immunised with the Polygen-adjuvanted tachyzoite preparation produced interferon-gamma concentrations of similar magnitude (P = 0.17) to those from the infected animals. Polygen was one of two adjuvants that elicited the highest antibody responses, and was the only adjuvant that induced interferon-gamma levels similar to those of the infected heifers.

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 explore the basis for this resistance, the erythropoietic response was evaluated in four native 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 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% 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 progenitors 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 an important impact on the early bone marrow response in primary T. congolense infection and confirmed previous suggestions of a high erythropoietic potential in trypanosome-infected young calves.

Rise in erythropoietin concentrations in experimental Trypanosoma congolense infection of calves

A bioassay was used to measure erythropoietin (EPO) concentrations in calves with haemorrhagic anaemia due to blood loss and in calves with anaemia due to Trypanosoma congolense infection. The bioactivity of EPO was measured in the assay by its stimulatory effect on 125I-deoxyuridine incorporation in spleen cells from phenylhydrazine-treated mice. Erythropoietin concentrations in blood-volume-depleted calves were elevated 6 h after blood loss, maximal (1225 mU/ml) at 33 h and below detection limits at 72 h. Reticulocytes (0.05 +/- 0.1%) appeared in blood by 72 h, peaked at 120 h and disappeared from the circulation by 7 days after bleeding. The packed cell volume (PCV) started increasing at 120 h and reached near pre-bleeding values by 14 days. In T. congolense-infected calves, parasites were first detected in the peripheral blood 12 days post-infection (dpi). Parasitaemia peaked (5 x 10(5) trypanosomes/ml of blood) at 15-18 dpi and, thereafter, several waves of parasitaemia were observed, but the peaks gradually diminished. Undiluted plasma from T. congolense-infected calves suppressed 125I-deoxyuridine incorporation into spleen cells from 13 dpi onwards. The suppressive effect of plasma was partly negated by five-fold dilution, which made possible the detection of increased EPO concentrations during the acute and chronic stages of the anaemia. The highest EPO peaks, reaching 2300 mU/ml in one calf, were detected during the chronic stage of the infection. At 15-39 dpi, there was a transient bone-marrow erythropoietic response characterized by an increase in mean corpuscular volume and a decrease in mean corpuscular haemoglobin concentration but with few reticulocytes (0.4%). However, from 76 dpi onwards, this response waned despite low PCV and elevated EPO concentrations. These results suggest that there is an ineffective erythroid response in the face of elevated EPO concentrations during bovine trypanosomiasis. The negative effect of plasma and serum from trypanosome-infected calves on the in-vitro bioactivity of EPO suggests the presence of inhibitory factors.

Trypanosoma congolense: comparative effects of a primary infection on bone marrow progenitor cells from N'Dama and Boran cattle

Using in vitro clonogenic assays, the changes in haemopoietic progenitor cell levels were compared in the bone marrow of three adult trypanotolerant N'Dama cattle and three age-matched trypanosusceptible Boran cattle over 17 weeks (119 days) of a primary Trypanosoma congolense (clone IL 1180) infection. As the infection progressed, a clear tendency of the parasitaemia to decrease was seen in the N'Damas, while it remained 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 neutrophils and monocytes in the blood observed in both breeds. Thereafter, a further significant drop in the CFU-GM levels was observed in the Borans which may partially explain the continued decrease in the numbers 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 the 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 levels in the Borans than in the N'Damas. The mean corpuscular volume (MCV) levels increased in both breeds, but at a much faster rate in the Borans. The clonogenic assays demonstrated an erythropoietic response, characterised by peaks above pre-infection levels of both the early and late erythroid progenitor cells (respectively, burst-forming units-erythroid, BFU-E, and colony-forming units-erythroid, CFU-E), occurring between 35 and 70 dpi in both breeds of cattle. However, despite a more severe anaemia in the Borans, the magnitude of their erythroid response was similar to that of the N'Damas, suggesting that the response of the Borans was insufficient to compensate for the greater degree of anaemia. Moreover, the mean PCV did not improve in the Borans, indicating the ineffectiveness of their erythropoietic response. An increased rate of erythrocyte destruction and/or a defective differentiation and maturation of erythroid precursors have also been shown to be partially responsible for this persistent anaemia. From 98 dpi onwards, despite the persistent low PCV, the MCV decreased to preinfection levels and 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%, which fell within the low normal range for cattle.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth on type I collagen promotes expression of the osteoblastic phenotype in human osteosarcoma MG-63 cells

Using MG-63 cells as a model system capable of partial osteoblastic differentiation, we have examined the effect of growth on extracellular matrix. MG-63 cell matrix and purified type I collagen induced a morphological change characterized by long cytoplasmic processes reminiscent of those seen in osteocytes. Concurrent biochemical changes involving bone marker proteins included increased specific activity of cell-associated alkaline phosphatase and increased secretion of osteonectin (up to 2.5-fold for each protein); all changes occurred without alterations in the growth kinetics of the MG-63 cells. The increase in alkaline phosphatase activity was maximal on days 6-8 following seeding; increased osteonectin secretion was most prominent immediately following seeding; all changes decreased as cells reached confluence. Growing cells on type I collagen resulted in an increased induction of alkaline phosphatase activity by 1,25(OH)2D3 (with little change in the 1,25(OH)2D3 induction of osteonectin and osteocalcin secretion), and increased TGF-beta induction of alkaline phosphatase activity as well (both TGF-beta 1 and TGF-beta 2). Both the 1,25(OH)2D3 and TGF-beta effects appeared to be synergistic with growth on type I collagen. These studies support the hypothesis that bone extracellular matrix may play an important role in osteoblastic differentiation and phenotypic expression.