Inhibition of African swine fever virus replication by β-glucan

Abstract

Background: African swine fever (ASF) is one of the most important diseases in pigs because of its effects on all ages and breeds. To date, commercial vaccines and drugs for the prevention of ASF are lacking in the market and the survival of African swine fever virus (ASFV) in various environmental, farm, and or feed matrices has allowed the virus to remain, causing new outbreaks in the pig population. Besides biosecurity and animal husbandry management practices, the improvement of the host immune responses is critical to control, managing, and preventing ASF.

Aim: In this study, we investigated the protective role of β-glucan against ASFV infection using a porcine alveolar macrophage (PAM) model.

Methods: The effects of β-glucan on cell proliferation were evaluated by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The potential effects of β-glucan against a field ASFV strain isolated in Vietnam were further examined by real-time PCR and hemadsorption assays. The interferon (IFN)-α and interleukin (IL)-6 protein production induced by β-glucan was determined using a sandwich enzyme-linked immunosorbent assay.

Results: Our results demonstrated that the β-glucan additive possessed an immune stimulus factor against ASFV. Specifically, protection of PAMs against ASFV infection in vitro was observed at 12 hours (p < 0.05) at the tested doses (30 and 50 µg/ml) as induced by incubation with β-glucan for 2 hours. These effects remained until 24 hours after post-infection. Additionally, at a high dose (50 µg/ml), pre-treatment with the β-glucan statistically increased the expression levels of IFNα and IL-6 when compared to untreated groups or only ASFV infection.

Conclusion: Together, these findings indicated that the β-glucan may protect the host against ASFV infection via the multiple cellular immune mechanisms.

Keywords: African swine fever virus; Cytokine; β-glucan.

Fig. 1.. (A) Chemical structures of β-glucan. (B) The effects of β-glucan on PAMs cell at the cell viability by MTT assay. The data are presented as the mean ± SEM of three independent experiments indicating the significant differences between the control and treatment groups were determined by a one-way analysis of variance. a: p < 0.05.

Fig. 2.. The antiviral activity of β-glucan against PAMs. PAMs were pre-treated with 30 µg/ml and 50 µg/ml β-glucan, and exposed to 10³ HAD₅₀/ml ASFV for 12, 24, or 36 hours. The viral DNA of ASFV in the supernatants was collected and then real-time PCR amplification of the p72 gene was performed to detect the presence of viral DNA in the PAMs treated with β-glucan. (A) Real-time PCR amplification of the p72 gene was performed to detect the presence of viral DNA at 12, 24, and 36 hours post-infection in the PAMs treated with β-glucan for 2 hours and then infected with 10³ HAD₅₀/ml ASFV; and (B) Titer of ASFV in the PAMs pre-treated with 30 or 50 µg/ml β-glucan in 2 hours and then exposed to 10³ HAD₅₀/ml ASFV at 12 and 24 hours post-treatment. The data were presented as the mean ± SEM of three independent experiments. *: p < 0.05.

Fig. 3.. Cytokine production by the PAMs infected with ASFV. PAMs were pre-treated with 30 or 50 µg/ml β-glucan for 2 hours and then exposed to 10³ HAD₅₀/ml ASFV for 12 (A, C) and 24 hours (B, D). The data are presented as the mean ± SEM of three independent experiments. *: p < 0.05.