Plasma-dependent, antibody- and Fcγ receptor-mediated translocation of CD8 molecules from T cells to monocytes.

CD8αβ heterodimers are mainly expressed on cytotoxic T lymphocytes. This study demonstrated the detection of CD8αβ heterodimers on human monocytes by whole blood erythrocyte lysis method in flow cytometry. Results revealed that CD8αβ heterodimers were not produced by monocytes themselves, but were transferred from T cells to monocytes when these cells were coincubated in plasma and with anti-CD8 monoclonal antibody (mAb). For completion of CD8 translocation from T cells to monocytes, cell-to-cell contact between T cells and monocytes, as well as binding of the Fc portion of the anti-CD8 mAb and Fcγ receptor II (FcγRII) on monocytes were required. Furthermore, the dynamism of cell membrane and cytoskeleton were involved in the mechanism of CD8 translocation. Interestingly, CD3 and αβT cell receptor (TCR) were also transferred from T cells to monocytes accompanied by CD8. These phenomena are consistent with Ab-dependent and FcγR-mediated trogocytosis, which is recently recognized as one of the intercellular communication processes of the immune system. Trogocytosis means exchange of plasma membrane including cell surface molecules in conjugates formed between immune cells. Results of this study could provide another model of trogocytosis and clearly indicated that putative plasma factors were critically implicated in the mechanism of Ab-dependent and FcγR-mediated trogocytosis.