Introduction
African swine fever (ASF) is an acute hemorrhagic disease of domestic
pigs. This disease often results in devastating economic losses to the
pig industries of suffered countries because of the high rates of
morbidity and mortality, and it is therefore classified as a notifiable
disease by the World Organization for Animal Health (OIE). An effective
vaccine is still not available so far, and control of the disease relies
mainly on rapid diagnosis and culling of infected pigs and close
contacted with them (Rowlands et al., 2008).
ASF was first recognized in early 1900’s in East Africa. Since then, it
has spread to most sub-Saharan African countries(Boshoff et al., 2007).
However, when the disease introduced in Georgia in the Caucasus in 2007
(Rowlands et al., 2008), it has spread subsequently toward the northern
and eastern areas of Europe with many countries affected, such as the
Russian Federation, Ukraine, and Poland (M. C. Gallardo et al., 2015;
Goller et al., 2015; Smietanka et al., 2016). In 2018, the first ASF
outbreak was reported in Liaoning Province in China (Ge et al., 2018;
Zhou et al., 2018). Since then, the disease has occurred in almost every
major pig production area of China (Tao et al., 2020). A recent
surveillance showed that naturally attenuated ASFVs have been identified
in several provinces of China, which makes the control situation of the
disease even more complex in the future (Sun et al., 2021). The disease
has also been reported in some other Asian countries recently (Mighell
et al., 2021).
ASF virus (ASFV) is the only member of Asfarviridae family
(Alonso et al., 2018). An ASFV virion has an overall icosahedral
morphology with a diameter of 260-300 nm. It is composed of five layers
including a viral core, a core shell, an inner lipid membrane, an
icosahedral capsid, and an external envelope (Wang et al., 2019). The
viral genome is a double-stranded DNA molecule of 170-190 kbp encoding
more than 150 viral proteins. About 50 of the viral proteins are
structural proteins that response for many important roles in the virus
life cycle, such as viral particle assembly and the infection of a host
cell; while the rest of them are non-structural proteins that are
expressed during viral replication and function mainly as regulators of
replication. Still, the functions of about 40 proteins of ASFV are
unknown yet (Alejo et al., 2018).
The pB602L protein of ASFV is encoded by B602L gene, which contains a
central variable region(CVR) and always severs as one of the targets for
sub-genotype classification of ASFV isolates (Atuhaire et al., 2013; C.
Gallardo et al., 2009; Mai et al., 2021; Owolodun et al., 2010). pB602L
is one of the non-structural proteins and functions as a molecular
chaperon the major structural protein p72, which formed aberrant
”zipper-like” structures instead of icosahedral virus particles in the
absent of pB602L during the viral capsid assembly (Epifano et al., 2006;
Liu et al., 2019). However, by which means that pB602L helps p72 to
assemble correctly is still a mystery. Previous studies showed that
pB602L has strong antigenicity and can be used to develop diagnostic
tools for ASFV(Gutierrez-Castaneda et al., 2008). Given that
live-attenuated ASFVs have been believed the most promising vaccination
strategies against ASFV (Chen et al., 2020; Sang et al., 2020), pB602L
is probability a suitable target for developing diagnostic tool for
evaluating the humoral immune responses of these vaccines because of the
antibodies against pB602Lproduced only after the expression of the
protein in the host cells.
In this study, we expressed and purified a recombinant pB602L of ASFV
strain HLJ/2018, which was then used as antigen to immunize mice for
monoclonal antibody (mAb) development. A total of eight mAbs were
obtained and they bound to three linear epitopes in pB602L. These
results provide biological materials and molecular basis for the basic
and applied researches on ASFV.