This micrograph shows a T cell hybridoma recognizing a specific T cell epitope on the surface of a Salmonella infected macrophage. Proteins secreted by Salmonella after uptake into the host cell can be identified by Tn5-DICE analysis (Ellefson et al., 2000). The Tn5-DICE transposon contains an MHC class 1 epitope that can be fused in-frame to any bacterial protein. Those bacterial proteins that reach the cytoplasm of an infected macrophage are processed and presented and, if they contain this epitope, the epitope is displayed on the surface of the cell. The micrograph shows a T cell hybridoma engineered to turn blue when it contacts a cell expressing this epitope. The engineered T cell hyridoma is courtesy of N. Shastri. The green dots within the cell on the left are Salmonella bacteria.

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