Immunopathological effects of experimental T-2 mycotoxocosis in broiler chicken co-infected with infectious bronchitis virus (IBV)

A total of 128 1-week-old chicks were classified into four groups; T-2 toxin fed (T-2), IBV infected (IBV), T-2 toxin fed and co-infected with IBV (T-2+IBV), and untreated (control) for a period of 6 weeks. Within their respective groups, the birds belonged to T-2 and T-2+IBV were exposed to 2 ppm of T-2 toxin contaminated feed for 6 weeks, and 0.2 ml of 10 EID(50) (10(5.69)/0.2 ml) inoculums of IBV isolate (India/LKW/56/IVRI/08) was used to challenge the chicks belonged to IBV alone and T-2+IBV groups after 3 weeks of the experiment. To study immunopathological effects, parameters such as lymphocyte stimulation indices (SI), haemagglutination inhibition, enzyme linked immunosorbant assay (ELISA), peripheral lymphocytes CD(4)(+) and CD(8)(+) analysis, and histopathological examination of lymphoid organs were done. Accordingly, SI values were significantly (P<0.05) lower in all the treatment groups as compared to control, however, the SI values of IBV infected group were significantly higher than the values in toxin fed groups. The mean HI titres to ND vaccine was significantly (P<0.05) lower in the toxin groups at all the intervals, and the antibody titres in IBV infected group were significantly (P<0.05) higher than that of T-2 toxin fed and co-infected with IBV group but were significantly (P<0.05) lower than the control at 21 (3) and 28 (10) days of toxin feeding (DTF) (days post infection (DPI)). Similarly, the mean IBV ELISA antibody titres in the toxin fed groups were significantly (P<0.01) reduced as compared with the IBV ELISA antibody titres of IBV infected but not toxin fed group, at all intervals. Peripheral CD(4)(+):CD(8)(+) ratios in T-2+IBV group and number of CD(4)(+) and CD(8)(+) peripheral lymphocytes in all treatment groups were significantly reduced as compared to the values in control birds. However, CD(4)(+):CD(8)(+) ratios of IBV infected group at 42 (21) DTF (DPI) were found significantly (P<0.05) higher than the values in control birds. Histopathologically, lymphoid organs (bursa of Fabricius, spleen, thymus, caecal tonsils and Harderian glands) showed moderate to severe necrosis (lymphocytolysis) and extensive lymphocyte depletion in all the toxin groups (T-2 and T-2+IBV groups) where the severity and extent of the lesions were more in T-2+IBV group. The findings of the present experiment revealed immunosuppressive effects of T-2 toxin and aggravated the pathology and pathogenesis of IBV infection.