Analyses of the primary in vitro responsiveness of non-immune porcine peripheral blood mononuclear cells with reference to immunization by African swine fever virus antigen and treatment with leucine methyl ester.

Peripheral blood mononuclear cells (PBMC) from non-immune pigs were immunized in vitro using African swine fever (ASF) virus antigen with concomitant mitogenic stimulations known to have varying effects on B and T lymphocyte activity. None of these conditions, including those previously reported as being successful for the in vitro immunization of non-immune porcine PBMC with ASF virus antigen, supported the induction of specific antibody. Due to the reports on in vitro immunization of human PBMC, attempts were made to control suppressor cell activity in the porcine PBMC from non-immune pigs through L-leucine methyl ester (Leu-OMe) treatment. Upon immunization of the Leu-OMe treated PBMC with ASF virus antigen, concomitant with mitogen or cytokine stimulations, no specific antibody production was detected. Nevertheless, aspecific porcine immunoglobulin secretion was observed. Further analysis of the PBMC responsiveness demonstrated that 2.5 mM Leu-OMe (the dose recommended for use with human PBMC) suppressed mitogen-induced porcine lymphocyte proliferation, but in the absence of any detectable cytotoxicity. In fact, both anti-ASF virus antigen specific immunization and stimulation with "T-lymphocyte" mitogens were suppressed, whereas pokeweed mitogen stimulation of B lymphocyte aspecific immunoglobulin secretion was unaffected. Consequently, it was not possible to immunize in vitro non-immune porcine PBMC with ASF virus antigen as had been previously reported, nor was it possible to transfer the technology successfully used with non-immune human PBMC to the in vitro stimulation/immunization of non-immune porcine PBMC. The furtherance of this work will require greater insight into the immunobiological parameters and dynamics of the stimulation of non-immune porcine peripheral blood leukocytes, which are not as simple as previously reported, nor the same as identified with human PBMC.