Cell lysates were incubated with indicated concentrations of peptide VNVDYSKL at 4C for 30 min, and subsequently incubated at 37C for 30 min. expression and abrogate antiviral CD8 T cell responses. == Introduction == Major histocompatibility complex (MHC) class I molecules play a critical role in antiviral immunity. A MHC class I molecule is composed of a heavy chain, a 2-microglobulin (2m) light chain, and a peptide of 8 to 10 amino acids in length. The majority of MHC class I-binding peptides is usually generated in the cytosol by proteasomes and transported into the lumen of the endoplasmic reticulum (ER) by transporter associated with antigen processing (TAP). Peptide loading onto the MHC class I heavy chain-2m heterodimer is usually facilitated by a multisubunit protein complex called the MHC class I peptide-loading complex (PLC) (Peaper and Cresswell, 2008). In addition to TAP and MHC class I, the PLC is composed of ER chaperones such as tapasin, ERp57, calreticulin, and protein disulfide isomerase. Upon peptide loading, the fully assembled MHC class I complexes dissociate from the PLC and transit to the cell surface. Recognition of viral peptides in the context of MHC class I molecules triggers virus-specific CD8 T cells to exert their effector functions including cytotoxicity and cytokine secretion (Guidotti Xantocillin and Chisari, 1996). To avoid detection by CD8 T cells, viruses have evolved various mechanisms to interfere with MHC class I antigen presentation (Hansen and Bouvier, 2009). Some viruses accelerate MHC class I turnover. Human cytomegalovirus (HCMV) US2 and US11 cause proteasomal degradation of MHC class I molecules by retrograde transport from the ER to the cytosol (Wiertz et al., 1996a;Wiertz et al., 1996b). The mK3 protein of murine gamma-herpesvirus 68 (MHV-68) induces proteasomal degradation of MHC class I as well as other components of the PLC (Boname et al., 2004;Lybarger et al., 2003;Stevenson et al., 2000). Kaposis sarcoma-associated herpesvirus (KSHV) K3 and K5, murine cytomegalovirus (MCMV) Rabbit Polyclonal to OR9Q1 m06/gp48, and myxoma computer virus leukemia-associated protein induce lysosomal degradation of MHC class I (Coscoy and Ganem, 2000;Guerin et al., 2002;Ishido et al., 2000;Reusch et Xantocillin al., 1999;Zuniga et al., 1999). An alternative strategy is usually retention of MHC class I molecules in the ER or ER-Golgi intermediate compartments. Adenovirus E3/19K, HCMV US3, and MCMV m152/gp40 fall into this category (Ahn et al., 1996a;Andersson et al., 1985;Jones et al., 1996;Liu et al., 2007;Ziegler et al., 1997). TAP appears to be an attractive target for viral inhibition of MHC class Xantocillin I biosynthesis. Herpes simplex virus (HSV) ICP-47 (Fruh et al., 1995;Hill et al., 1995;York et al., 1994), HCMV US6 (Ahn et al., 1997;Hengel et al., 1997;Lehner et al., 1997), varicellovirus UL49.5 (Koppers-Lalic et al., 2005;Koppers-Lalic et al., 2008), and BNLF2a of Epstein-Barr computer virus (Hislop et al., 2007) were shown to interfere with TAP function to limit the supply of peptides for loading onto MHC class I. These viral inhibitors of MHC class I expression have yielded insight into normal MHC class I synthesis and assembly. Thein vivosignificance of these viral MHC class I evasion mechanisms however, is not well comprehended and somewhat controversial. In a mouse model of HSV-1, ICP-47 was shown to enhance neurovirulence (Goldsmith et al., 1998). However, this data should to be interpreted with caution because ICP-47 has minimal effect on murine MHC class I (Ahn et al., 1996b). MHV-68 and MCMV, on the other hand, efficiently inhibit murine MHC class I. Whereas mK3-deficient MHV-68 failed to establish a normal Xantocillin latent load (Stevenson et al., 2002), MCMV lacking all known MHC class I evasion genes (m04, m06, m152) did not demonstrate attenuated virulence unless they were tested in immunocompromised or newborn mice (Doom and Hill, 2008). Furthermore, to our knowledge, it has not been clearly demonstrated how the evasion of MHC class I antigen presentation affects the pathogenesis of non-herpesviruses. In this regard, it is noteworthy that cowpox computer virus (CPXV) has recently been shown to downregulate MHC class I and evade antiviral CD8 T cell responses (Dasgupta et al., 2007). CPXV belongs toOrthopoxvirusgenus of the poxvirus family, which also includes other clinically important pathogens such as variola computer virus, the causative agent of smallpox, and monkeypox computer virus. Wild rodents are believed to be the natural reservoir hosts of CPXV in Europe (Chantrey et al., 1999). Like other orthopoxviruses, CPXV encodes a large number Xantocillin of immune evasion genes in its DNA genome (Seet et al., 2003). One of such genes, CPXV203, was shown.
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