Figure 3.

Distribution of interferon gamma (IFN-γ) mRNA positive cells localized by in situ hybridization in cecum and liver. A distinct distribution pattern of cytokine mRNA positive cells in the primarily affected organs was evident between groups of turkeys that received only attenuated parasites and those inoculated with virulent Histomonas meleagridis. Representative distribution patterns are given using IFN-γ mRNA positive cells with areas of positive cells indicated by red arrows. At 4 days post-inoculation (DPI), positive cells were rarely distributed in caeca which then became abundant at 7 and 10 DPI with accumulation of positive cells being restricted to the lamina propria of birds that receive the attenuated culture (A), whereas virulent histomonads triggered further distribution of positive cells to the muscularis layer with losing of the mucosal fold at 10 DPI (B). In livers, positive cells were occasionally found as sporadic cells studded between hepatocytes and lymphoid aggregates (C) or in more expansive distribution comprising mononuclear infiltrates when affected by virulent histomonads (D).