Transfer of macrophage-derived mycobacterial antigens to dendritic cells can induce naïve T-cell activation.

Mycobacteria are capable of surviving and replicating in host macrophages, where they can release antigenic material into the environment. However, unlike dendritic cells (DCs), macrophages do not appear to be capable of activating naïve T cells. Therefore, this work investigated antigen transfer between macrophages and DCs. We generated culture supernatants from bacille Calmette-Guérin (BCG)-infected and uninfected macrophages and then determined whether DCs could present these extracellular mycobacterial antigens to T cells. Here, we show that DCs pulsed with antigens released from BCG-infected macrophages can stimulate primed T cells in vitro and initiate naïve T-cell responses in vivo. These results suggest that antigen transfer can occur between macrophages and DCs.