Tong GZ, Zhou YJ, Hao XF, et al. Emergence of the high pathogenic porcine reproductive and respiratory syndrome in China[J]. Emerging Infectious Diseases, 2007, 13(9):1434-1436. [2] Zhou YJ, Hao XF, Tan ZJ, et al. Highly virulent porcine reproductive and respiratory syndrome virus emerged in China[J]. Transbound Emerge Dis, 2008, 55(3-4):152-164. [3] Tian K, Yu X, Zhao T, et al. Emergence of fatal PRRSV variants:unparalleled outbreaks of a typical PRRS in China and molecular dissection of the unique hallmark[J]. PLoS One, 2007, 6:1-10. [4] Zhou Z, Ni J, Cao Z, et al. The epidemic status and genetic diversity of 14 highly pathogenic porcine reproductive and respiratory syndrome virus(HP-PRRSV)isolates from China in 2009[J]. Veterinary Microbiology, 2011, 150:257-269. [5] Allende R, Laegreid WWL, Kutish GF, et al. Porcine reproductive and respiratory syndrome virus:description of persistence in individual pigs upon experimental infection[J]. J Virol, 2000(74):10834-10837. [6] Zhou EM, Clavijo A, Jiang Z, et al. Induction of auto-anti-idiotypic antibodies specific for antibodies to matrix and envelope glycoprotein from pigs experimentally infected with porcine reproductive and respiratory syndrome virus[J]. Veterinary Immunology and Immunopathology, 2004, 101:49-59. [7] Oleksiewicz MB, Butner A, Toft P, et al. Emergence of porcine reproductive and respiratory syndrome virus deletion mutants:relation with the porcine antibody response to a hyper variable site in the ORF3 structural glycoprotein[J]. J Virology, 2000, 267:135-142. [8] Drew TW, Paul Lowings J, Yapp F. Variation in open reading frames 3, 4 and 7 among porcine reproductive and respiratory syndrome virus isolates in the UK[J]. Veterinary Microbiology, 1997(55):209-221. [9] Delputte PL, Vanderheijden N, Nauwynck HJ, et al. Involvement of the matrix protein in attachment of porcine reproductive and respiratory syndrome virus to a heparin-like receptor on porcine alveolar macrophages[J]. J Virol, 2002, 76:4312-4320. [10] Bastos RG, Dellagostin OA, Barletta RG, et al. Immune responses of pigs inoculated with Mycobacterium bovis BCG expressing a truncated form of GP5 and M protein of porcine reproductive and respiratory syndrome virus[J]. Vaccine, 2004, 22:467-474. [11] Nakhai B, Pal R, Sridhar P, et al. The alpha subunit of human chorionic gonadotropin hormone synthesized in insect cells using a baculovirus vector is biologically active[J]. FEBS Lea, 1991, 283:104-108. [12] Jones I, Morikawa Y. Baculovirus vectors for expression in insect cells[J]. Curropin Biotechnical, 1996, 7:512-516. [13] Tjia ST, zu Alteuschildesche GM, Doerfler W. Autographa califomica nuclear polyhedrosis virus(AcNPV)DNA does not persist in mass culture of mammalian cells[J]. Virology, 1983, 125:107-117. [14] Voikman LE, Goldsmith PA. In vitro survey of Autographa californica nuclear polyhedrosis virus interaction with nontarget vertebrate host cells[J]. Appl Environ Microbiol, 1983, 45:1085-1093. [15] Carbonell LF, Klowden MJ, Miller LK. Baculovirus-mediated expression of bacterial genes in dipteran and mammalian cells[J]. J Viral, 1985, 56:153-160. [16] Murtaugh MP, Xiao PZ, Zuckermann F. Immunological responses of swine to porcine reproductive and respiratory syndrome virus infection[J]. Viral Immunol, 2002, 15:533-547. [17] Lopez OJ, Osorio FA. Role of neutralizing antibodies in PRRSV protective immunity[J]. Vet Immunol Immunopathol, 2004, 102:155-163. [18] Dea S, Gagnon CA, Mardassi H, et al. Antigenic variability among North American and European strains of porcine reproductive and respiratory syndrome virus as defined by no clonal antibodies to the matrix protein[J]. J Clinical Microbiol, 1996, 34:1488-1493.