coronaviruses (SARS coronavirus) and lentiviruses (Human Immunodeficiency Virus (HIV)). However, IFITM proteins did not affect alphavirus, arenavirus, or murine leukaemia virus infection. IFITM proteins inhibit viral membrane and cellular endosomal or lysosomal vesicle membrane fusion by modifying their lipid components or fluidity. IFITM proteins block the hemifusion stage of entry, an intermediate stage in which portions the outer membranes of the target cell and the viral envelope mix prior to completion of fusion. Furthermore, IFITM proteins reduced membrane fluidity and affected membrane curvature to restrict viral membrane fusion with the cellular membrane. In addition, IFITM3 interacted with the cellular cholesterol regulatory proteins vesicle associated membrane protein A (VAPA) and oxysterol binding protein (OSBP) to induce intracellular cholesterol accumulation, which in turn blocks viral membrane and vesicle membrane fusion. References Further reading External links Clusters of differentiation