Figure 6. A model of T helper cell priming by extracellular HSPs.
The release of HSPs from tumor cells (or introduced through vaccination) into the extracellular environment has the potential to stimulate APCs through CD91. The APCs will advertise HSP-specific effects through a unique pattern of co-stimulation (cytokines described here and co-stimulatory molecules [13]) in the draining lymph nodes where they prime Th cell subsets of different types. These effects are nevertheless influenced by other cytokines the tumor cells themselves may release like TGF-β.