Role of the capsid protein VP4 in the plasma-dependent enhancement of the Coxsackievirus B4E2-infection of human peripheral blood cells

Abstract It has been previously shown that antibodies contained in human plasma directed towards the Coxsackievirus B4 (CVB4)E2 capsid protein VP4 can enhance the CVB4E2-induced production of IFN-α by peripheral blood mononuclear cells (PBMC). The aim of this study was to produce a VP4 fusion protein to investigate the role of the internal capsid protein VP4 and anti-VP4 antibodies in the plasma-dependent enhancement of CVB4E2 infection of PBMC. A fusion protein MBPVP4 containing the VP4 insert of CVB4E2 and a control fusion protein MBP-β-gal-α, were produced in Escherichia coli K12 TB1. The CVB4E2 infection of PBMC was quantified by using a real time PCR method amplifying CVB4E2-negative strand RNA. IFN-α concentrations in culture supernatants were assayed by DELFIA. MBPVP4 but not MBP-β-gal-α, preincubated with plasma inhibited the plasma-dependent enhancement of CVB4E2-induced production of IFN-α by PBMC. Human plasma samples, antibodies contained in plasma eluted from MBPVP4-coated plates, but not from MBP-β-gal-α-coated plates, incubated with CVB4E2 enhanced the infection of PBMC and the production of IFN-α by infected cells. Together our results show that VP4 and anti-VP4 antibodies play a role in the plasma-dependent enhancement of CVB4E2 infection of PBMC.