The Binding of Thymus Leukemia (TL) Antigen Tetramers to Normal Intestinal Intraepithelial Lymphocytes and Thymocytes

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Abstract
Thymus leukemia (TL) Ags belong to the family of nonclassical MHC class I Ags and can be recognized by both TCRαβ and TCRγδ CTL with TL, but not H-2 restriction. We previously reported that the CTL epitope is TAP independent, but the antigenic molecule(s) presented by TL has yet to be determined. In the present study, TL tetramers were prepared with T3b-TL and murine β2-microglobulin, not including antigenic peptides, and binding specificity was studied. CTL clones against TL Ags were stained with the T3b-TL tetramer, and the binding shown to be CD3 and CD8 dependent. Normal lymphocytes from various origins were also studied. Surprisingly, most CD8+ intraepithelial lymphocytes derived from the small intestines (iIEL), as well as CD8+ and CD4+CD8+ thymocytes, were stained, while only very minor populations of CD8+ cells derived from other peripheral lymphoid tissues, such as spleen and lymph nodes, were positive. The binding of T3b-TL tetramers to CD8+ iIEL and thymocytes was CD8 dependent, but CD3 independent, in contrast to that to TL-restricted CTL. These results altogether showed that TL-restricted CTL can be monitored by CD3-dependent binding of T3b-TL tetramers. In addition, CD3-independent T3b-TL tetramer binding to iIEL and thymocytes may imply that TL expressed on intestinal epithelium and cortical thymocytes has a physiological function interacting with these tetramer+CD8+ T lymphocytes.