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BY55 is a human cell surface molecule whose expression is restricted to NK cells, a subset of circulating CD8+ T lymphocytes, and all intestinal intraepithelial T lymphocytes. Here, we report that BY55 is a novel NK receptor showing broad specificity for both classical and nonclassical MHC class I molecules, and that optimal binding requires a prior aggregation of MHC class I complexes. Using BY55 transfectants, we have identified functional consequences of MHC class I/ligand interactions for the class I-bearing cell. The triggering of MHC class I molecules on human T cell clones by BY55 delivered a potent proliferative signal in the presence of soluble CD3 mAb. The costimulatory signal provided by MHC class I ligation was only seen in activated, and not resting, peripheral blood T cells. This observation represents an additional and/or alternative pathway to CD28 costimulation and may be of particular relevance in memory T cells lacking CD28, such as intestinal intraepithelial T lymphocytes, which are CD28- but BY55+.

Type

Journal article

Journal

J Immunol

Publication Date

01/02/1999

Volume

162

Pages

1223 - 1226

Keywords

Animals, Antigens, CD, CD28 Antigens, Cell Line, Cricetinae, GPI-Linked Proteins, HLA-A2 Antigen, Histocompatibility Antigens Class I, Humans, Killer Cells, Natural, Ligands, Lymphocyte Activation, Membrane Proteins, Mice, Receptors, Immunologic, Recombinant Proteins, Signal Transduction, Solubility, T-Lymphocytes, Transfection