| The present study considered the properties, the specificity, and the regulation of natural killer (NK) cells in Yorkshire swine. Peripheral blood lymphocytes were found to possess high levels of NK activity, particularly against YAC-1, K-562, P-815, and TU-5 targets. Kinetic studies showed NK lysis in Yorkshire swine is delayed, beginning six hours after mixing effectors and targets. This delayed lysis was due to a refractoriness in the NK lytic mechanism because target binding, which was shown to be necessary for target lysis, occurred within minutes. Morphologically, the NK effector in Yorkshire swine was found to be a medium sized agranular lymphocyte, and not the large granular lymphocyte reported in other species. The significance of this finding as it relates to the slower NK kinetics is discussed. Analysis of NK activity by the single cell-mediated cytotoxicity assay in agarose showed this procedure can be used as an index of swine NK activity. Energy studies indicated swine NK cell lysis is dependent on energy derived from respiration and glycolysis. Two treatments, ammonium chloride and pre-storage at 37(DEGREES)C, were found to have an effect on NK activity which varied with the target employed, thus suggesting the swine NK population is heterogeneous. Like other species, swine NK cells were found to be nonadherent effectors with a characteristic tissue distribution. NK activity was high in peripheral blood, intermediate in spleen, low in lymph nodes, and absent in the thymus. Specificity studies, using cold target competition and monolayer adsorption assays, demonstrated swine NK cells recognize multiple determinants and strongly inferred the existence of subsets with common and unique target cell specificities. The regulation of swine NK cells was assessed using polyinosinicpolycytidylic acid (Poly I:C), a substance which induces interferon, a potent NK stimulant. Preliminary studies showed Poly I:C increased NK activity against all cell lines tested. However, the dose response pattern varied with the target, suggesting the swine NK population is not equally sensitive to Poly I:C treatment. Poly I:C did not alter the kinetics of lysis, and appeared to increase the number of lytic cells in the NK population. |
