title: Resting porcine T lymphocytes expressing class II major histocompatibility antigen.
abstract: The immune system of swine is unique in that the expression of CD4 and CD8 antigens defines four subpopulations of resting, extrathymic (CD1-) T lymphocytes in the circulation as well as in lymphoid tissue. Here it is documented that the specialty of the porcine T lymphocyte compartment extends to the expression of class II MHC (SLA) antigens. While the TCR gamma/delta CD4-CD8- as well as the TCR alpha/beta CD4+CD8- subpopulation both lack MHC II, the TCR alpha/beta CD4-CD8+ and the CD4+CD8+ subpopulation, the latter of which is private to swine, both do express MHC II. As opposed to human T lymphocytes, expression of porcine MHC II is not transient and restricted to lymphoblasts but is imminent in small, resting T lymphocytes of the two CD8-expressing subsets, even though also in swine activation can induce MHC II. Activation-induced extrathymic acquisition of MHC II without reversal can be discussed as one possible way of how MHC II+ T lymphocytes are generated. Alternatively, MHC II antigens should already be expressed by thymic progenitors. Remarkably, all CD1+CD4-CD8+ and most CD1+CD4+CD8+ thymocytes lack MHC II, yet, a minor subset with the phenotype CD4hiCD8hi expresses MHC II. One may speculate that these cells do not undergo thymic selection and represent the progenitors of the unusual, swine-typic MHC II+CD4+CD8+ extrathymic T lymphocytes.
authors.affiliation: Federal Research Center for Virus Diseases of Animals, Tübingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Saalmüller
authors.forename: F
authors.initials: F
authors.lastname: Weiland
authors.forename: M J
authors.initials: MJ
authors.lastname: Reddehase
mesh_terms: D000818:Animals; D015704:CD4 Antigens / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology; D005434:Flow Cytometry; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis*; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex / Q000276:immunology*; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta; D013234:Stem Cells / Q000276:immunology; D013552:Swine / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology; D015854:Up-Regulation
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D000949:Histocompatibility Antigens Class II; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta