The expression of the major histocompatibility complex (MHC) classical class I genes is important for the adaptive immune response to target virus-infected cells and cancer cells. The up-regulation of the MHC is achieved by hormonal/cytokine signals including IFN-gamma-inducible elements. The swine leukocyte antigen (SLA), the MHC class I region of pigs, consists of the duplicated classical class I genes, SLA-1, SLA-2 and SIA-3, but the molecular mechanisms involved in their up-regulation after T cell stimulation have not been fully elucidated. In order to better understand some of the putative regulatory mechanisms of SLA class I gene expression in aCtivated T cells, we examined the coordinated expression of the SLA classical class I, IFN-gamma and interferon regulatory factor-1 (IRF-1) genes in the peripheral blood mononuclear cells (PBMCs) of SLA homozygous Clawn miniature swine stimulated for 72 h with either IFN-gamma or an enterotoxin produced by Staphylococcus aureus. This enterotoxin, toxic shock syndrome-1 (TSST-1), is known to act as a superantigen (SAG) to activate the T cells in various vertebrate species. We showed by using mAbs and flow cytometry that the CD4(+)CD25(+) cell number of swine PBMCs was also increased by TSST-1 and to a lesser degree by IFN-gamma. Time course analyses of the expression of the IFN-gamma, IRF-1 and the three classical class I genes, IFN-g, SIA-2, and SIA-3, in PBMCs by quantitative real-time PCR revealed a transitory response to TSST-1 or IFN-gamma stimulation. The IFN-gamma mRNA levels in the PBMCs were continuously up-regulated over the first 48 h by TSST-1 or IFN-gamma. In contrast, Slit class I expression moderately increased at 24 h and then decreased to a baseline level or less at 72 h of IFN-gamma or TSST-1 stimulation. The three classical SLA class I genes showed similar expression kinetics, although SIA-3 mRNA level was consistently lower than those of SIA-1 and -2. The expression of IRF-1, a modulator of SLA expression, showed similar kinetics to those of the three classical SLA class I genes. The expression profiles detected by flow cytometry of the SLA molecules on the cell surface of PBMCs were maintained at a consistently high level during cell stimulation with either TSST-1 or IFN-gamma, which was distinct from the kinetics of mRNA expression. These results showed that miniature swine SLA class 1 mRNA expression was effectively and equally up-regulated among the three loci and coordinately with IRF-1 gene expression after stimulation of T cell activation by sAG or IFN-gamma. (c) 2012 Elsevier B.V. All rights reserved.