Cytokine expression in the eye and brain of chickens following infection with a very virulent plus Marek's disease virus strain

Abstract

Cytokine transcripts were evaluated chronologically in the brain and in the eye of chickens infected with the very virulent plus Marek's disease virus (vv + MDV) strain 648A. Brain and eye samples were collected from chickens that were either suffering from transient paralysis (TP) (11 days post inoculation, dpi) or had completely recovered from TP but started developing clinical signs of persistent neurological disease (PND) (18-31 dpi). Results obtained from samples collected at 11 dpi are referred as EL (early lesions) and results obtained from samples collected at later times (18-31 dpi) are referred as LL (late lesions). Marked differences were found in the cytokine transcripts in brain and eye. While proinflammatory cytokines (IL-1β, IL-8, IL-18), iNOS, IFN-α, IFN-γ, and IL-15 were upregulated in the brain during EL and LL, only IL-8 and IFN-γ were upregulated in the eye at both times (EL and LL). The two evaluated viral transcripts (gB and meq) were found in both eye and brain during EL and LL. Levels of the two viral transcripts evaluated were higher at LL than at EL in both brain and eye. No differences were found in any of the viral transcripts between eye and brain during EL. However, during the LL, the levels of meq transcripts were higher in the eye than in the brain. Our results suggest that MDV elicits different immune responses in the brain and in the eye of infected chickens. Because immune responses in the eye of chickens have been poorly studied, further studies on the pathogenesis of MDV in the eye could greatly contribute to our knowledge on the chicken eye immunity.

Keywords: Brain; Chicken; Cytokine; Eye; Marek’s disease; Transient paralysis.