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Two Groups of Porcine TCR⁺ Thymocytes Behave and Diverge Differently¹

Marek inkora^2,*, Jana inkorová, Zdenk Cimburek and Wolfgang Holtmeier

^* Department of Immunology and Gnotobiology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nov Hrádek, Czech Republic; Art and Research Technologies, Nov Hrádek, Czech Republic; Department of Immunology and Gnotobiology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic; and Johann-Wolfgang Goethe University, Medical Clinic I, Department of Gastroenterology, Frankfurt, Germany

Developmental pathways of T cells are still unknown, largely because of the absence of recognized lineage-specific surface markers other than the TCR. We have shown that porcine thymocytes can be divided into 12 subsets of the following two major groups: 1) CD4^– thymocytes that can be further subdivided according to their CD2/CD8 phenotype, and 2) CD4⁺ thymocytes that are always CD1⁺CD2⁺CD8⁺ and have no counterpart in the periphery. In this study, we have analyzed thymocyte subsets with respect to behavior during cultivation, cell cycle status, and lymphocyte-specific transcripts. The group of CD4^– thymocytes gives rise to all T cells found in the periphery. Proliferating CD2⁺CD8^–CD1⁺CD45RC^– thymocytes are a common precursor of this group. These precursors differentiate into CD2⁺CD8⁺, CD2⁺CD8^–, and CD2^–CD8^– T cell subsets, which subsequently mature by loss of CD1 and by eventual gain of CD45RC expression. In contrast, the group of CD4⁺ thymocytes represents transient and independent subsets that are never exported from thymus as TCR⁺ T cells. In accordance with the following findings, we propose that CD4⁺CD8⁺ thymocytes extinguish their TCR expression and differentiate along the T cell lineage program: 1) CD4⁺ thymocytes are actively dividing; 2) CD4⁺ thymocytes do not die, although their numbers decreased with prolonged cultivation; 3) CD4⁺ thymocytes express transcripts for RAG-1, TdT, and TCR; and 4) CD4⁺ thymocytes are able to alter their phenotype to TCR⁺ thymocytes under appropriate culture conditions.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work has been supported by Grants 524/04/0543 and 524/07/0087 from the Grant Agency of the Czech Republic, Grant A5020303 from the Grant Agency of the Academy of Sciences of the Czech Republic, and Institutional Research Concept AV0Z 50200510.

² Address correspondence and reprint requests to Dr. Marek inkora, Department of Immunology and Gnotobiology, Institute of Microbiology, Czech Academy of Science, Doly 183, 549 22 Nov Hrádek, Czech Republic. E-mail address: Marek.Sinkora{at}worldonline.cz

³ Abbreviations used in this paper: DG, day of gestation; 7-AAD, 7-aminoactinomycin D; Cy5, cyanine 5; FCM, flow cytometry; LC, constant portion of Ig L chain.