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Figure 10.9 Photomicrograph illustrating histopathological changes: foci of acute hepatic necrosis with heterophil rich inflammatory
infiltrates and the classic large intranuclear basophilic viral inclusions, characteristic features of inclusion body hepatitis (IBH). H&E, 400 ×
magnification. Courtesy of Dr Marina Brash, Animal Health Laboratory, University of Guelph.

1998; Pierson and Fitzgerald, 2013; Dhama et al., 2017). The effects on cells of the adaptive immune system (de Waal Malefyt,
microscopic lesions are most evident in the intestinal tract and in 1991). IL-8 is expressed by activated macrophages and secreted
the immune system. In the spleen, hyperplasia of white pulp and to recruit immune cells, mainly neutrophils, to the site of infec-
lymphoid necrosis are seen. Cowdry type B intranuclear inclusion tion (Modi et al., 1990). IL-18 is also produced in macrophages
bodies in the lympho-reticular cells can be observed (Saunders et and stimulates NK and certain T-cells to release IFN-γ (Biet et
al., 1993; Suresh and Sharma, 1996). Lymphoid necrosis in the al., 2002).
bursa of Fabricius and thymus have been described (Hussain et Upon infection with FAdV-4 (ON1 isolate), transcription
al., 1993; Suresh and Sharma, 1995). The typical lesions of the levels of IFNγ and IL-10 are significantly higher in liver at 3 dpi,
intestinal tract include congestion of the mucosa, haemorrhage of whilst levels of IL-8 and IL-18 remain unchanged. IFNγ and IL-18
tips of the villi and necrosis. Inclusions bodies can also be found mRNA levels in spleen are significantly lower in FAdV-4 infected
in a variety of organs (Itakura and Carlson, 1975; Meteyer et al., birds at 10 dpi, whilst their levels remain nearly unchanged in
1992; Trampel et al., 1992). caecal tonsils (Grgić et al., 2013a).
Upon FAdV-8 infection, transcription of IFN-γ and IL-10
is up-regulated and down-regulated, respectively, in spleen of
Immune response birds at 3 dpi. IL-18 expression in spleen is up-regulated at 1 dpi
and down-regulated at 7 dpi. IL-8 expression seems to remain
Innate immunity unchanged until 7 dpi, time after which the expression of this
Studies on the innate immunity in response to avian adenovirus cytokine is significantly down-regulated up to 10 dpi. In caecal
infections are limited. In general, type I IFNs and pro-inflammatory tonsils, IFN-γ, IL-18 and IL-10 mRNA levels are increased at 1
cytokines are rapidly expressed in response to infection to limit dpi, though their levels do not differ significantly with respect to
virus replication and stimulate the acquired immunity. those from uninfected birds. IL-8 expression seems to be down-
Infections with FAdV-4, FAdV-8 and FAdV-9, and likely all regulated, but its levels seem not to differ significantly to those
aviadenoviruses, up-regulate the expression of type I and II from controls. In liver, IFN-γ is significantly up-regulated at 3, 5,
IFNs (IFN-α and IFNγ, respectively) in all studied tissues such and 7 dpi. IL-10 is also found up-regulated in infected chickens at
as liver, caecal tonsil, spleen and bursa of Fabricius, whilst the 1, 3, and 5 dpi. Expression levels of IL-8 and IL-18 significantly
expression of other cytokines (IL-10, IL-8 and IL-18) seems to increase at 3 dpi, while IL-8 seems to decrease at 5, 7, and 10 dpi
be tissue-dependent (Deng et al., 2013; Grgić et al., 2013a,b). (Grgić et al., 2013b).
IFNγ is an essential cytokine for innate and adaptive immunity IFN-α, IFNγ and IL-12 mRNAs are up-regulated in liver of
against pathogens including viruses. This cytokine is produced FAdV-9-infected chickens. IFN-α is detected at 3, 5 and 7 dpi
by NK and natural killer T (NKT) cells as well as by activated and declines by 14 dpi, whilst levels of IFNγ mRNA is detected
CD4 Th1 and CD8 T-cells (Schoenborn and Wilson, 2007). at 3 and 5 dpi and remain significantly high up to 14 dpi. IL-12
IL-10 has both immunosuppressive and immunostimulating is found up-regulated at 3, 5, 7 and 14 dpi. IL-10 mRNA levels