|WANG, DAN - Shandong Agricultural University|
|FITZGERALD, SCOTT - Michigan State University|
|SUN, SHUHONG - Shandong Agricultural University|
Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2016
Publication Date: N/A
Interpretive Summary: Marek’s disease virus (MDV), the etiological agent of Marek’s disease (MD), is a herpes virus that causes the suppression of immune system and evasion of immune responses in the infected chickens. In this study we investigated the immunosuppressive effect of MDV infection on the development of necrotic combs and toes in the MDV-resistant and susceptible chicken lines. Gene expression analysis of MDV-infected chickens revealed up regulation of immune-related genes in the necrotic combs of the MDV-infected resistant line. The expression levels of most of the tested genes were lower in the combs of the susceptible line with no apparent necrotic dermatitis in the combs. Histopathological analysis showed thinning and erosion of epidermis and inflammation within the connective tissues of the necrotic combs. No virus particle was detected in the necrotic combs of the resistant or susceptible line. Gram staining of the sectioned frozen comb tissues, however, exposed the presence of Staphylococcus species. This study provides evidence that necrotic dermatitis observed in the combs and toes of MD-resistant line 63 is a clear example of the unintended outcome of line selection for MD resistant that has negatively affected the immunological competence of the birds to immunosuppressive agents and secondary bacterial infection.
Technical Abstract: Marek’s disease (MD), a lymphoproliferative disorder of domestic chickens is characterized by bursal–thymic atrophy and rapid onset of T-cell lymphomas that infiltrate lymphoid tissues, visceral organs, and peripheral nerves. Marek’s disease virus (MDV), the etiological agent of MD, is a highly cell-associated oncogenic '-herpesvirus that replicates in chicken lymphocytes and establishes a latent infection within CD4+ T cells. We investigated the immunosuppressive effect of MDV infection on the development of necrotic dermatitis in the combs of two MD-susceptible (72) and resistant (63) chicken lines at 21 days post infection. MDV-infected birds of line 63 are relatively resistant to tumor development but exhibit an unusual necrosis of combs, wattles, and toes that is intensified when infected with MDV. Chickens from Line 72, on the other hand, are highly susceptible to MDV infection and tumor development. Real-Time PCR analysis revealed that IL-6, Il-8, IL-12, IL-18, iNOS, and INF' were all up regulated in the necrotic combs of MDV-infected line 63. The expression levels of most of the tested genes were lower in the combs of the susceptible line with no visible necrotic damage. No MDV antigen but a massive infiltration of macrophages and lymphocytes was detected in the comb tissues of both resistant and susceptible lines. Histopathological analysis also revealed thinning and erosion of epidermis and inflammation, lympho-plasmocytic infiltration, heterophilic and histocytic cellulitis within the connective tissues of the necrotic combs. Gram stain of the sectioned frozen comb samples exposed the presence of Staphylococcus species.