Cross-dressers turn on T cells

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Abstract
Memory T cells remember viruses from previous infections, providing immunity by facilitating the killing of infected cells. For this, they exploit cross-dressing, the transfer of antigens between antigen-presenting cells. See Letter p.629 A novel mechanism for the activation of naive CD8+ T cells was identified in 2005. Termed cross-dressing, in recognition of the cross-priming and direct priming mechanisms known previously, it involves the transfer of loaded MHC/peptide molecules from an infected cell to dendritic cells. Linda Wakim and Michael Bevan now show that memory T-cell activation in viral infection occurs in part through cross-dressing. As an alternative mode of antigen presentation to memory T cells during viral infection, cross-dressing avoids the need for antigen processing by the presenting dendritic cell and allows prompt presentation of peptide epitopes that closely reflect those expressed on infected cells.