title: MHC class II-alpha chain knockout mice support increased viral replication that is independent of their lack of MHC class II cell surface expression and associated immune function deficiencies.
abstract: MHCII molecules are heterodimeric cell surface proteins composed of an α and β chain. These molecules are almost exclusively expressed on thymic epithelium and antigen presenting cells (APCs) and play a central role in the development and function of CD4 T cells. Various MHC-II knockout mice have been generated including MHC-IIAα(-/-) (I-Aα(-/-)), MHC-IIAβ(-/-) (I-β(-/-)) and the double knockout (I-Aαxβ(-/-)). Here we report a very striking observation, namely that alphaviruses including the avirulent strain of Semliki Forest virus (aSFV), which causes asymptomatic infection in wild-type C57BL6/J (B6) mice, causes a very acute and lethal infection in I-Aα(-/-), but not in I-β(-/-) or I-Aαxβ(-/-), mice. This susceptibility to aSFV is associated with high virus titres in muscle, spleen, liver, and brain compared to B6 mice. In addition, I-Aα(-/-) mice show intact IFN-I responses in terms of IFN-I serum levels and IFN-I receptor expression and function. Radiation bone marrow chimeras of B6 mice reconstituted with I-Aα(-/-) bone marrow expressed B6 phenotype, whereas radiation chimeras of I-Aα(-/-) mice reconstituted with B6 bone marrow expressed the phenotype of high viral susceptibility. Virus replication experiments both in vivo and in vitro showed enhanced virus growth in tissues and cell cultures derived form I-Aα(-/-) compared to B6 mice. This enhanced virus replication is evident for other alpha-, flavi- and poxviruses and may be of great benefit to producers of viral vaccines. In conclusion, I-Aα(-/-) mice exhibit a striking susceptibility to virus infections independent of their defective MHC-II expression. Detailed genetic analysis will be carried out to characterise the underlining genetic defects responsible for the observed phenomenon.
authors.affiliation: Department of Immunology, The John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia. mohammed.alsharifi@adelaide.edu.au
authors.forename: Mohammed
authors.initials: M
authors.lastname: Alsharifi
authors.forename: Aulikki
authors.initials: A
authors.lastname: Koskinen
authors.forename: Danushka K
authors.initials: DK
authors.lastname: Wijesundara
authors.forename: Jayaram
authors.initials: J
authors.lastname: Bettadapura
authors.forename: Arno
authors.initials: A
authors.lastname: Müllbacher
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000276:immunology / Q000821:virology; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D006224:Cricetinae; D000949:Histocompatibility Antigens Class II / Q000235:genetics* / Q000276:immunology*; D007153:Immunologic Deficiency Syndromes / Q000235:genetics / Q000276:immunology* / Q000821:virology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012672:Semliki forest virus / Q000276:immunology; D014709:Vero Cells; D014779:Virus Replication / Q000235:genetics / Q000276:immunology*
chemical_list: D000949:Histocompatibility Antigens Class II