Introduction

African swine fever virus is one of the most threatening diseases for swine industry of the world. World Organization for Animal Health (OIE) list ASFV as a notifiable disease(Sanchez-Vizcaino, Mur, Gomez-Villamandos, & Carrasco, 2015). Since ASFV was first identified in Kenya in 1921, it has spread to most sub-Saharan countries, Europe, the Caribbean, South America and China(Muñoz-Moreno, Galindo, Cuesta-Geijo, Barrado-Gil, & Alonso, 2015).. African swine fever is a highly contagious and lethal viral disease of swine has had a significant socioeconomic impact in the developed and developing word, making it a global animal health priority(Agüero et al., 2003). African swine fever caused by African swine fever virus has caused huge economic losses to the world pig industry. Since it was first found in Portugal, up to now, there have been three transcontinental spreading. On the third transcontinental spread occurred into China in 2018, from 2018 to 2019, more than 169,000 pigs were slaughtered(Zhou et al., 2018).
African swine fever virus (ASFV) is the only one of theAsfarviridae family, it belongs to a 170-194 kb double-stranded DNA virus(Chapman et al., 2011). The genome encodes for more than 150 polypeptides, at least 50 of which result in production of the structural proteins that comprise the different domains of the viral particles(Heimerman et al., 2018). ASFV has more than 100 unique proteins, such as p30, p54, p72, pp220, p17, CD2V, p10, p12(Jia, Ou, Pejsak, Zhang, & Zhang, 2017). ASFV contains at least 68 different structural proteins and 21 cellular proteins(Alí, Tania, Milagros, & Germán, 2018). Among the structural proteins, p30 also named p32 which appears early during ASFV infection(Alonso et al., 2001; Barderas et al., 2001). P30 protein was determined to be a highly immunogenic protein and stimulates the highest level of antibody response during ASFV post infection in pig (Giménez-Lirola et al., 2016).
ASFV p30 protein is an early phosphorylated protein encoded byCP204L gene which is one of the most immunogenic proteins(Afonso et al., 1992; Prados, Viñuela, & Alcamí, 1993). P30 protein located in the inner membrane of the viral envelope(Kolontsov, Ustin, Shubina, Piria, & Makarov, 1992). ASFV p30 protein could induce neutralizing antibodies in immunized pigs, and p30 was shown to be involved in various steps of virus attachment and internalization(Giménez-Lirola et al., 2016). P30 protein is highly immunogenic, which can be expressed at 2 to 4 hours after infection, and then continue the whole infection cycle(Gómez-Puertas et al., 1998). Therefore, the expression of ASFV p30 indicates that the virus has entered but not coated, and the virus gene has been expressed. Related studies have shown that p30 protein is the most diagnostic antigen. So, the diagnosis based on monoclonal antibody of p30 is of great significance for early prevention and control of ASF(Petrovan et al., 2019).
In our study, we expressed and purified p30 protein, then produced three mAbs against p30 protein. Two novel linear p30 B cell epitopes,1MDFILNISMKMEVIFKTDLR20 and26VFHAGSLYNW35 were subsequently identified using these three mAbs. All of them could be recognized by anti-ASFV positive sera. Moreover,1MDFILNISMKMEVIFKTDLR20 and26VFHAGSLYNW35 are highly conserved among 19 genotypes. These findings provide valuable information for virus diagnosis.