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. 2013 Jan 24;9(1):e1003124. doi: 10.1371/journal.ppat.1003124

Figure 5. IFITM proteins inhibit cell-cell fusion induced by representatives of three classes of viral fusion proteins.

Figure 5

(A to E) Effector cells expressing indicated viral fusion proteins were loaded with calcein-AM, and were bound to target 293/LH2SN cells (Mock) or to cells expressing indicated IFITM proteins that were prelabeled by CMAC. pH was then lowered to 5.0 for JSRV Env, 4.8 for IAV HA, 5.7 for VSV G, and 5.4 for SFV E1/E2. Following reneutralization of cells to 7.2, fusion between pairs of effector and target cells was scored under fluorescence microscopy. (A) IAV HA (a class I fusion protein). (B) VSV G (class III). (C) SFV E1/E2 (class II). (D) JSRV Env (class I), with COS7 as effector cells. (E) JSRV Env, with 293T cells as effector cells. Note distinct effects of IFITM3 on JSRV fusion shown in (D) and (E). (F) Restriction of JSRV and IAV entry by IFITM proteins in COS7/LH2SN cells. COS7/LH2SN cells (Mock) or derivatives expressing indicated IFITM proteins were infected with GFP-encoding MoMLV pseudovirions bearing JSRV Env or IAV HA/NA, and viral infectivity was determined by flow cytometry as described in Fig. 1. Note that IFITM3 inhibited JSRV entry as effectively as did the IFITM1; representative flow cytometry profiles are shown in Fig. S4A.