The fusion mechanism is the mechanism by which cell fusion takes place. Cell fusion is the formation of a hybrid cell from two different cells of different species. Cells from the same organism may fuse together as well. This is often observed during lytic viral infection, where alterations of the cell can be seen under a light microscope. These include changes in morphology, formation of vacuoles and fusion of cells to form syncytia.
The term cell fusion mechanism refers to the receptors required for cells to fuse, whereas the term cell fusion refers to the action of formation of the new cell.
One example of the cellular fusion mechanism is that of HIV infecting the body. HIV infects by fusing with the membranes of immune system cells. In order for HIV to fuse with a cell, it must be able to bind to the receptors CD4, CCR5, and CXCR4.