Modulation of the immune responses in chickens by low-pathogenicity avian influenza virus H9N2.
Most low-pathogenicity avian influenza (LPAI) viruses cause no or mild disease in avian species. Little is known about the mechanisms of host defence and the immune responses of avian influenza-infected birds. This study showed that chicken macrophages are susceptible to infection with LPAI H9N2 and H6N2 viruses and that infection led to apoptosis. In H9N2 virus-infected chicken macrophages, Toll-like receptor 7 responded to infection and mediated the cytokine responses. Whilst pro-inflammatory cytokines were largely upregulated, the interferon (IFN) response was fairly weak and IFN-inducible genes were differentially regulated. Among the regulated genes, major histocompatibility complex (MHC) antigens II were downregulated, which also occurred in the lungs of H9N2-infected chickens. Additionally, interleukin (IL)-4, IL-4 receptor and CD74 (MHC class II invariable chain) were also downregulated, all of which are pivotal in the activation of CD4+ helper T cells and humoral immunity. Remarkably, in H9N2 virus-infected chickens, the antibody response was severely suppressed. This was in contrast to the robust antibody response in chickens infected with H6N2 virus, in which expression of MHC class II antigens was upregulated. These data suggest that neutralizing antibodies and humoral immunity may not be developed efficiently in H9N2-infected chickens. These findings raise questions about how some LPAI viruses differentially regulate avian immune responses and whether they have similar effects on mammalian immune function.
Xing
Zheng
Z
Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Cardona
Carol J
CJ
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Li
Jinling
J
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Dao
Nguyet
N
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Tran
Tu
T
Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Andrada
Jason
J
Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D000944:Antigens, Differentiation, B-Lymphocyte / Q000096:biosynthesis; D017209:Apoptosis; D002645:Chickens; D016207:Cytokines / Q000096:biosynthesis; D005786:Gene Expression Regulation; D006385:Hemagglutination Inhibition Tests; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis; D053127:Influenza A Virus, H9N2 Subtype / Q000276:immunology* / Q000472:pathogenicity; D005585:Influenza in Birds / Q000276:immunology*; D008264:Macrophages / Q000821:virology; D019948:Receptors, Interleukin-4 / Q000096:biosynthesis; D051199:Toll-Like Receptor 7 / Q000276:immunology
D000914:Antibodies, Viral; D000944:Antigens, Differentiation, B-Lymphocyte; D016207:Cytokines; D000949:Histocompatibility Antigens Class II; D019948:Receptors, Interleukin-4; D051199:Toll-Like Receptor 7; C045084:invariant chain