Submitted to: Viral Immunology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/17/2012
Publication Date: 8/1/2012
Citation: Xu, M., Fitzgerald, S.D., Zhang, H., Karcher, D.M., Heidari, M. 2012. Very virulent plus strains of MDV induce acute form of transient paralysis in both susceptible and resistant chicken lines. Viral Immunology. 25(4):306-323. Interpretive Summary: Marek’s Disease (MD) is a cancer-like disease of chickens caused by a herpesvirus named Marek’s disease virus (MDV). Clinical signs of MD include depression, crippling, weight loss, and transient paralysis (TP). TP is a disease of the central nervous system, which affects the MD-susceptible chickens 8-11 days post inoculation (dpi), normally resulting in recovery 1-3 days after the onset of clinical sign. Very virulent strains of MDV, however, induce an acute form of TP that results in mortality shortly after the onset of clinical signs. Data from our recent study revealed that birds inoculated with a highly pathogenic strain of MDV had higher expression levels of several immune proteins known as cytokines and chemokines. Also, the expression levels of some of these immune components named IL-6, IL-10, IFN-alpha, IFN-beta, and IFN-gamma were significantly higher in the brain tissues of the chickens exhibiting clinical signs of TP compared with non-symptomatic MDV-infected chickens. This gene expression profiling points toward a possible underlying immunological mechanism for viral-induced TP and the differential responses of the two chicken lines to MDV infection. This information is important in understanding the pathogenicity of the disease and will lead to better control methods.
Technical Abstract: Marek’s Disease (MD) is a lymphoproliferative disease of domestic chickens caused by a highly cell-associated alpha herpesvirus, Marek’s disease virus (MDV). Clinical signs of MD include depression, crippling, weight loss, and transient paralysis (TP). TP is a disease of the central nervous system, which affects the MD-susceptible chickens 8-11 days post infection (dpi), normally resulting in recovery 1-3 days after the onset of clinical sign. In this study we inoculated chickens from lines 72 (MD-susceptible) and 63 (MD-resistant) with a very virulent plus strain of MDV at two weeks of age and collected brain samples from birds with and without TP at 5, 11, and 21 dpi for gene expression profiling and histological analysis. Data revealed that chickens inoculated with MDV had higher levels of IL-6, IL-10, IL-18, IFN-alpha, IFN-beta, IFN-gamma, MHC I, and CD18 in their brains at 11 dpi compared to the uninfected control birds. In addition, the expression levels of IL-6, IL-10, IFN-alpha, IFN-beta, and IFN-gamma were significantly higher in the brains of the birds showing clinical signs of TP in comparison to asymptomatic chickens. Comparative analysis between the two chicken lines showed that the expression levels of IL-6, IL-10, IFN-beta, IFN-gamma, IL-18, CD18, and MHC I were significantly higher in the brains of the birds from line 63 with TP than those of line 72 exhibiting neurological disorders. Differential expression pattern was observed for some of the tested genes at different time points post inoculation. Histological analysis showed lymphocytic meningitis, perivascular cuffing, and neuronal degeneration within the brains of birds from both susceptible and resistant lines exhibiting TP at 11 dpi. Vaccination prevented development of TP and other MD-associated clinical symptoms. These observations are suggestive of an underlying immunological mechanism for viral-induced neurological dysfunctions and the differential responses of the two chicken lines to MDV infection.