PhD

In this investigation the pathological effects of OA in quail embryo and adult quail were studied with special reference to the immune system. Ochratoxin A (OA) was inoculated into the quail embryos, at the dose rate of 0.02 µg per embryo. There was 68.66 per cent mortality which clearly indicated the direct action of OA. The embryos which were sacrificed on the 13th and 16th day of incubation showed significant reduction in the body weight, weight of bursa of Fabrics, spleen and thymus. Histological changes in these lymphoid organs were, atrophy, necrosis and depletion of lymphoid elements.
Ultrastructurally the changes were time dependent. There were changes in the shape of the nucleus with condensation of granular and fibrillar components of the nucleoli. The adverse immunobilogical effect of OA on the developing lymphoid organs was established by histological and ultra structural studies.
OA at the dose rate of 50 µg /bird/day for a period of 60 days was administered through oesophageal intubation. Pathological changes were sequentially documented with special reference to the immune system.
In the OA fed quails, the clinical signs included emaciation and hyperexcitation at the later part of the experiment. There was highly significant reduction in the body weight, weight to bursa of Fabricius, spleen and thymus. The reduction in the weight of lymphoid organs gave evidence to the adverse effects of OA on the immune system.
There was reduction in the total erythrocyte count (TEC), haemoglobin (Hb) concentration and packed cell volume in OA fed birds indicating the significant damaging effect on the heamopoietic system. Estimation of total serum protein (TSP), serum globulin (SGI) and serum immunoglobulin fractions clarified the biological adverse effect of OA on the humoral immune system. Highly significant reduction in total leukocyte count (TLC) and T cell dependent lymphopenia proved the immunosuppressive effect of OA.
There was reduction in T cells, increase migration indices in response to Fowl pox antigen in leukocyte migration inhibition test (LMIT), the reduction in the cutaneous response to 2, 4 – dinitrochlorobenzene (DNCB) and phytohaemagglutinin – M (PHA – M) and spleen indices in the graft versus host reaction (GVHR), clarified the immunotoxicity of OA on the cell – mediated immune system.
Grossly the OA fed birds had pale, friable liver, congested and haemorrhagic kidney, mild enteritis, atrophied bursa of Fabricius, spleen and thymus. Thymus showed petechial haemorrhages and brain revealed cerebral congestion. The lymphoid organs showed degenerative changes and loss of lymphoid elements. Ultrastructurally the bursa of Fabricius showed alteraction in lymphoid and epithelial components, lytic cytoplasm and nuclear condensation. The transformation of lymphoid cells into plasmacytoid series of cells was lacking. Similar cellular changes were also seen in the spleen and thymus. These changes gave evidence for the clinical manifestation of defective humoral and cell – mediated response. Kidney tubules were dilated and necrosis of the proximal convoluted tubules was seen along with congestion and focal haemorrhages. Thickening of the glomerular basement membrane was evident. Ultrastructurally fragmentation and lysis of plasma membrane at the luminal surface, numerous cytoplasmic vacuoles and fusion of podocyte foot processes were seen. Liver showed varying degree of fatty change. Ultrastructurally mitochondrial swelling and abnormal mitochondria to severe cytolytic changes were observed. Brain showed, focal oedema, Pyknosis, Karyorrhexis, satellitosis of microglial cells and swollen vascular endothelium. This was supported by electron microscopic observations of separation of neuronal elements, fragmentation and vacuolation of perineuronal elements. No gross or histological changes were seen in the heart.
Immunostimulation with levamisole at the dose rate of 0.1 mg/quail two doses at 4 day interval, resulted in lymphocytic leucocytosis. TSP and SGI levels were increased significantly associated with increase in IgM and IgG. T cell associated lymphocytosis, decreased migration indices in response to Fowl pox antigen in LMIT, increased cutaneous response to DNCB and PHA – M, were also recorded. There was also elevation of TEC, Hb concentration and PCV.
The histological examination of lymphoid organs of immunostimulated quails revealed hyperplasia and blastoid transformation in the bursa of Fabricius, spleen and thymus.
This study brought to light the immunotoxicity of OA on the humoral and cell – mediated immune system. In addition to this, adverse effects on hepatic, haemopoietic and nervous systems were also documented. Levamisole was demonstrated to regulate the immunodeficiency induced by OA in quails.