Monitoring the Interaction Between Dendritic Cells and T Cells In Vivo with LIPSTIC

: Interactions between different cell types are key for immune function. Traditionally, interactions have been investigated in vivo by intravital two-photon microscopy, but the molecular characterization of the cells participating in a specific interaction is limited by the inability to retrieve the cells for downstream analysis. We recently developed an approach to label cells undergoing specific interactions in vivo, which we called LIPSTIC (Labeling Immune Partnership by Sortagging Intercellular Contacts). Here, we provide detailed instructions on how to track CD40-CD40L interactions between dendritic cells (DCs) and CD4+ T cells using genetically engineered LIPSTIC mice. This protocol requires expertise in animal experimentation and multicolor flow cytometry. Once mouse crossing has been achieved, it takes 3 days or more to complete, depending on the kinetics of the interactions that the researcher wishes to investigate.