INTERFERON INDUCTION IN PERIPHERAL-BLOOD MONONUCLEAR LEUKOCYTES OF MAN AND FARM-ANIMALS BY POXVIRUS VECTOR CANDIDATES AND SOME POXVIRUS CONSTRUCTS

Prototypes of three poxvirus genera-orthopoxvirus (OPV), parapoxvirus (PPV), avipoxvirus (APV)-and Newcastle disease virus (NDV) as a control, as well as three recombinant OPV strains and one recombinant APV strain, were incubated in vitro with peripheral blood mononuclear leukocytes (PBML) of man, sheep and swine. Antiviral activity was determined in PBML culture supernatants at different time intervals after virus cell interaction using a cytopathic effect inhibition bioassay. Additionally, supernatants derived from human PBML were screened for interferons (IFN) alpha and gamma as well as for tumor necrosis factor by enzyme-linked immunosorbent assay. IFN titers reached a maximum 24 h after PBML stimulation at a multiplicity of infection (MOI) greater than 1. IFN alpha/beta was found to be responsible for the antiviral effect. Using a MOI greater than or equal to 1 the highly attenuated strain MVA was the only representant of vaccinia virus (VV) that induced significant amounts of IFN also as a lacZ recombinant. Replicable virus from five well-known VV strains as well as the Chinese VV strain Tien Tan (VV TT) as a recombinant vaccine failed to induce leukocyte IFN. Inactivated VV strain Elstree and the recombinant TT strain induced high titers of leukocyte IFN. Supernatants derived from human, porcine and ovine PBML stimulated with replicable PPV, native VV MVA and MVA lacZ recombinant or native APV and APV lacZ recombinant virus regularly contained IFN alpha. In contrast to NDV, neither specific antisera nor monoclonal antibodies were able to block the INF induction by VV and PPV.