| The mycotoxin, aflatoxin B (AFB1) is a polycyclic aromatic hydrocarbon, produced by some strains of the ubiquitous fungi Aspergillus flavus, A. parasiticus and A. nomius, found to be a potent immunomodulator in endotherms. Exposure to AFB1 results in the reduction of cytokine production of bovine macrophages and T-cells. Animals and birds exposed to AFB1 exhibit reduced macrophage function, suppressed cell mediated immunity and humoral immunity. The phagocytic capacity of the macrophages reduced in nile tilapia after aflatoxin exposure. Embryonic exposure of rainbow trout to AFB1 results in reduced B-cell memory. A dramatic suppression of immunoglobulin production and lymphocyte proliferation was marked when rainbow trout peripheral blood leucocytes were exposed to AFB1. Although canine, one of the important species is also susceptible to aflatoxicosis, little is known about the effect of AFB1 on the immune system of this species. The study related to immunosuppression due to AFB1 in canine is limited. In the present study, we applied several methods to evaluate the immune response of hybrid dogs to different time of exposing to AFB1.In this present study, a range of hybrid dogs were selected to determine the canine lymphocytic proliferation effects in different time after the dogs were exposed to AFB1, respectively, the changes of subgroup T lymphocytes, by the methods of lymphocytic transfer proliferation MTT and SAP. Otherwise, the level of Parvovirus IgG was determined by an ELISA method. At 8 weeks before experiment, dogs were vaccinated with parvovirus vaccine. After 8 weeks, were fed a diet contaminated with 340μg AFB1/kg feed. At different time (0,7,14,21 and 28) intervals blood samples were aseptically collected from the anterior limb vein. Blood was collected in tubes containing EDTA for blood culture or blood formula, respectively. Plasma samples were obtained following centrifugation of heparinized blood and stored at -20℃for later analysis.The results were as follows:1. Effects of time and PBMC, Con A, LPS of different concentration on promote lymphocytes proliferation was tested by MTT test. The result of experiment demonstrate that the best levels combination of canine lymphocyte. In the lymphocytic transfer test, Con A at dosage of 80μg/mL performed facilitation effects for canine lymphocytic proliferation(p>0.05),when the best levels combination of canine T lymphocyte was 1×106 unit/mL, the incubated time for 48h. LPS at 100μg/mL markedly proliferated B lymphocytes(p<0.05),with the best levels combination of canine B lymphocyte was 1×107 unit/mL, the incubated time for 20h.2. With LPS and Con A, respectively, stimulate canine T and B lymphocytic proliferation, at 7 days, the proliferation ability of canine T lymphocytes became markedly stronger(P<0.05). From 14 to 28 days, the proliferation of T lymphocytes showed a downtrend. The proliferation ability of canine B lymphocytes became markedly to weaken, from 7 to 28 days, compare to 0 days. Also at 21 days, the ability was stronger than those of 14 and 28 days. The number of lymphocyte in canine peripheral blood did not be impaired.3. With regard to lasting of the time, a significant down-regulation of all subgroup T lymphocytes was observed in canine blood. The ratio of CD4+/CD8+ was down, according to the analysis of the reducing of CD4+ T-cells was stronger than CD8+ T-cells.4. AFB1 exposure had no major effect on the level of Parvovirus IgG.So it can be concluded here that either AFB1 can markedly impaired canine cellular mediated immunity, which put forward certain powerful experimental evidences and instructions for diagnosis of canine diseases especially canine expose to AFB1 diseases. These impairments in the immune response could participate in failure of vaccination protocols and increased susceptibility to infections described in dogs exposed to AFB1. |
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