We have developed a system of porcine peripheral blood mononuclear cells for the synthesis of
antibodies in vitro, induced by partially purified African swine fever virus particles inactivated with
formaldehyde. The
antibodies synthesized were detected by a radioimmunoassay with a sensitivity of 3 ng of
immunoglobulin. Primary responses were dependent on supernatants from peripheral blood mononuclear cells incubated with
concanavalin A, macrophages and T lymphocytes. Secondary responses did not require
concanavalin A-
conditioned medium. The kinetics of antibody synthesis was similar in both primary and secondary responses, but the extent of synthesis was four to five times larger in the secondary than in the primary response. The
antibodies synthesized in vitro were specific for African swine fever virus
antigens (and did not react with
viral antigen other than that from African swine fever virus particles), in contrast to
pokeweed mitogen-induced
antibodies, which reacted with all the
antigens tested. African swine fever virus-induced
antibodies did not neutralize the virus. These results and the inability of the virus to stimulate a primary response in the absence of
concanavalin A supernatants indicate that inactivated African swine fever virus is not a polyclonal stimulator.