Physiological and therapeutic relevance of T cell receptor-mediated antigen trogocytosis.

Trogocytosis is an active process whereby fragments of plasma membrane proteins and cytoplasm are transferred from one cell to another in a cell-cell contact-dependent manner. T cells trogocytose pieces of the cells presenting antigen to them at the site of the immunological synapse. Fragments of the antigen-presenting cell membrane rich in antigen/major histocompatibility (MHC) complexes are internalized by the T cell. Those complexes are redirected to the plasma membrane of the T cell, which subsequently becomes an antigen-presenting cell to other T cells. Removing antigen/MHC complexes from professional and tumoral cells has consequences for the intensity and duration of the immune response. However, the acquired capacity of T cells to present the trogocytosed cognate antigen/MHC complexes also affects the properties of the trogocytotic T cells. Acting as antigen-presenting cells, trogocytotic CD4 T cells influence both the differentiation of cytotoxic T cells and the differentiation of other CD4 T cells into pro-inflammatory effector T cells. Furthermore, trogocytosis of antigen/MHC complexes promotes the differentiation of the trogocytotic CD4 T cells towards regulatory T cells and Th2 effector cells. Trogoctyosis is, therefore, a parallel mechanism to signal transduction by membrane receptors, including the T cell antigen receptor, at the plane of the plasma membrane.