Cutting edge: In situ tetramer staining of antigen-specific T cells in tissues.

Staining Ag-specific T cells with fluorescently labeled tetrameric MHC/peptide complexes has provided a powerful experimental approach to characterizing the immune response. In this report, we describe an extension of this method to directly visualize Ag-specific T cells in tissues. We successfully stained transgenic T cells with MHC tetramers in spleen sections from both 2C and OT-1 TCR transgenic mice. In addition, with the in situ tetramer staining technique, we detected a very small population of Ag-specific T cells in tissue after adoptive transfer of transgenic TCR T cells to a syngeneic nontransgenic mouse. We also show that the in situ tetramer technique can be applied to lightly fixed as well as frozen tissue, thus extending the method to archived tissue collections. This in situ tetramer staining technique offers a general approach to tracking the Ag-specific T cells in tissues.