T Cells Capture Bacteria by Transinfection from Dendritic Cells

Recently, we have shown, contrary to what is described, that CD4(+) T cells, the paradigm of adaptive immune cells, capture bacteria from infected dendritic cells (DCs) by a process called transinfection. Here, we describe the analysis of the transinfection process, which occurs during the course of antigen presentation. This process was unveiled by using CD4(+) T cells from transgenic OTII mice, which bear a T cell receptor (TCR) specific for a peptide of ovoalbumin (OVAp), which therefore can form stable immune complexes with infected dendritic cells loaded with this specific OVAp. The dynamics of green fluorescent protein (GFP)-expressing bacteria during DC-T cell transmission can be monitored by live-cell imaging and the quantification of bacterial transinfection can be performed by flow cytometry. In addition, transinfection can be quantified by a more sensitive method based in the use of gentamicin, a non-permeable aminoglycoside antibiotic killing extracellular bacteria but not intracellular ones. This classical method has been used previously in microbiology to study the efficiency of bacterial infections. We hereby explain the protocol of the complete process, from the isolation of the primary cells to the quantification of transinfection.