MHC transfer from APC to T cells following antigen recognition.

Recognition of cognate MHC:peptide complexes by T cells leads to large-scale molecular rearrangements resulting in immunological synapse formation at the T cell-antigen-presenting cell (APC) interface. Although the functions of the immunological synapse are not completely understood, a consequence of this event appears to be the intercellular transfer of MHC:peptide complexes, along with other molecules such as CD80, from the APC to the T cell. The expression of APC-derived molecules on the T cell is biologically significant. It has the potential to alter the homing, allow T cells to also act as APC, and may alter the effector functions of the cell. Experimental evidence suggests that intercellular transfer may play a role in the control of an immune response; however, the exact role is unclear. Both potentiation and attenuation of an ongoing response have been postulated. In addition, removal of molecules from APC may be important in controlling homeostatic proliferation, in affinity maturation of T cells, and in maintaining epitope diversity during an immune response. In this review, we highlight recent advances regarding the mechanism of intercellular transfer and focus on the potential biological significance of this event.