In order to infect and persist in their hosts, viruses utilize multiple strategies to evade the immune system. HIV utilizes membrane interacting regions of its envelope protein, primarily used to fuse with its target cells, to inhibit T-cell activation. Yet, it is unknown whether this ability is shared with other viruses. We examined the T-cell inhibitory activity of HTLV-1, focusing on a functionally conserved region of HTLV’s and HIV’s fusion proteins, the fusion peptide (FP). Here, we reveal that HTLV’s FP modulates T-cell activity in-vitro and in-vivo. This modulation is characterized by downregulation of the Th1-response, leading to an elevated Th2-response observed by transition in mRNA, cytokines and regulatory proteins. Our findings suggest that FP mediated immune evasion might be a trait shared between different viruses.
