Myxovirus- and coronavirus-induced in vitro stimulation of spontaneous cell-mediated cytotoxicity by porcine blood leukocytes

Spontaneous cell-mediated cytotoxicity (SCMC) by porcine blood leukocytes toward human myeloid tumour target cells (K(562)) was shown by Koren and coworkers in 1978, using a 4-h (51)Cr-release assay. In the present paper, SCMC was found to be enhanced following a 24-h incubation of leukocytes with swine influenza virus (SIV) of the H(3)N(2) type, and with the transmissible gastroenteritis virus (TGEV), a porcine coronavirus. In most of our experiments, both SIV and TGEV induced interferon (IFN) production by leukocytes (titres ranging from 30-7,500 units/ml). When porcine leukocytes were incubated with TGEV in the presence of anti-IFN antiserum, no SCMC stimulation occurred, suggesting that the virus-induced SCMC stimulation was mainly due to endogenously produced IFN. On the other hand, when either human αIFN or porcine virus-induced IFN were added to porcine leukocytes, a rapid and marked SCMC increase was observed. Both the SIV-induced SCMC increase and IFN production were suppressed when SIV was UV-inactivated. On the contrary, UV-inactivated TGEV was still able to enhance SCMC and to induce IFN production by porcine leukocytes. On the whole, these results suggest that myxovirus and coronavirus are able to activate porcine leukocyte SCMC via endogenously produced IFN.