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T‐cell development: an extrathymic perspective
Author(s) -
Blais MarieÈve,
Louis Isabelle,
Perreault Claude
Publication year - 2006
Publication title -
immunological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.839
H-Index - 223
eISSN - 1600-065X
pISSN - 0105-2896
DOI - 10.1111/j.0105-2896.2006.00341.x
Subject(s) - biology , haematopoiesis , microbiology and biotechnology , lymphopoiesis , t cell , progenitor cell , immunology , stem cell , immune system
Summary: The lymph nodes (LNs) harbor a cryptic T‐lymphopoietic pathway that is dramatically amplified by oncostatin M (OM). OM‐transgenic mice generate massive amounts of T lymphocytes in the absence of Lin – c‐Kit hi IL‐7Rα – lymphoid progenitors and of reticular epithelial cells. Extrathymic T cells that develop along the OM‐dependent LN pathway originate from Lin – c‐Kit lo IL‐7Rα + lymphoid progenitors and are different from classic T cells in terms of turnover kinetics and function. Positive selection does not obey the same rules in the thymus and the LNs, where positive selection of developing T cells is supported primarily by epithelial and hematopoietic cells, respectively. Extrathymic T cells undergo enhanced homeostatic proliferation and thereby acquire some properties of memory T cells. Following antigen encounter, extrathymic T‐cells initiate proliferation and cytokine secretion more readily than classic T cells, but their accumulation is limited by an exquisite susceptibility to apoptosis. Studies on in vitro and in vivo extrathymic T‐cell development have yielded novel insights into the essence of a primary T‐lymphoid organ. Furthermore, comparison of the thymic and OM‐dependent extrathymic pathways shows how the division of labor between primary and secondary lymphoid organs influences the repertoire and homeostasis of T lymphocytes.