Inhibition of transmissible gastroenteritis coronavirus (TGEV) multiplication in vitro by non-immune lymphocytes

In vitro studies were undertaken to examine the effects of non-immune porcine peripheral blood leukocytes (PBL) on a Coronavirus infection due to transmissible gastroenteritis virus (TGEV). The assay consisted of TGEV-infected epithelial cells expressing viral antigens on the cell surface and producing low amounts of interferon (IFN). Non-immune PBL were found to limit virus replication at an effector-to-target ratio of 100/1 even when effector cells were depleted of phagocytic cells. Neutralizing anti-IFN antibodies did not abrogate the effect. PBL from newborn animals were as effective as adult cells, whereas fibroepithelial cells, human and mouse lymphoid cells did not exert antiviral effects. Under similar conditions, PBL from adult animals could lyse TGEV-infected cells even in the presence of anti-IFN antibodies. However, newborn PBL were not cytotoxic. Moreover, depletion of NK cells by monoclonal antibodies plus complement did not alter the inhibitory effect. These latter observations suggest that virus multiplication-inhibition effects and cytotoxic (or NK) activities are unrelated.