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Although human and bovine γδ T cells were shown to express MHC class II antigen and function as APCs, attempts to determine if mouse γδ T cells have similar functions remained unsuccessful. We now show that γδ T cells derived from immunized mice also can be induced to express MHC class II and co-stimulatory molecules after activation in vitro, and are capable of antigen presentation. Using highly purified γδ T cells, we found that, unlike human γδ T cells, the expression of MHC class II molecules by mouse γδ T cells is limited to newly activated cells. Highest levels of MHC class II expression were seen on activated γδ T cells that had lost most surface-expressed γδ TCR while exhibiting increased levels of intracellular γδ TCR. In the absence of further stimulation, MHC class II expression gradually declined with the γδ T cells regaining their surface TCR. We also show that cytokine-activated γδ T cells can also …