The Virological Synapse Facilitates Herpes Simplex Virus Entry into T Cells

The virological synapse (VS) is a specialized molecular structure that facilitates the transfer of certain lymphotropic viruses into uninfected T cells. However, the role of the VS in the transfer of nonlymphotropic viruses into T cells is unknown. Herpes simplex virus (HSV) has been shown in vitro to infect T cells and modulate T-cell receptor function, thereby suppressing T-cell antiviral function. However, whether such infection of T cells occurs in vivo is unknown. Here, we examined whether T-cell infection could be observed in human HSV disease and investigated the mechanism of HSV entry into T cells. We found that HSV-infected T cells were readily detectable during human disease, suggesting that infection and modulation of T-cell function plays a role in human immunopathology. HSV infection of both CD4⁺ and CD8⁺ T cells occurred much more efficiently via direct cell-to-cell spread from infected fibroblasts than by cell-free virus. Activation of T cells increased their permissivity to HSV infection. Cell-to-cell spread to T cells did not require HSV glycoproteins E and I (gE and gI), which are critical for cell-to-cell spread between epithelial cells. Transfer of HSV to T cells required gD, and the four known entry receptors appear to be contributing to viral entry, with a dominant role for the herpesvirus entry mediator and nectin-1. VS-like structures enriched in activated lymphocyte function-associated antigen 1 (LFA-1) were observed at the point of contact between HSV-infected fibroblasts and T cells. Consistent with spread occurring via the VS, transfer of HSV was increased by activation of LFA-1, and cell-to-cell spread could be inhibited by antibodies to LFA-1 or gD. Taken together, these results constitute the first demonstration of VS-dependent cell-to-cell spread for a predominantly nonlymphotropic virus. Furthermore, they support an important role for infection and immunomodulation of T cells in clinical human disease. Targeting of the VS might allow selective immunopotentiation during infections with HSV or other nonlymphotropic viruses.The virological synapse (VS) is a specialized molecular structure that facilitates the transfer of certain lymphotropic viruses, such as human immunodeficiency virus (HIV) and human T-cell leukemia virus type 1 (HTLV-1), into uninfected T cells (22, 28, 38). Entry and infection of T cells by HIV or HTLV-1 via the VS is far more efficient than infection by cell-free virus, and thus this structure plays a critical role in the pathogenesis of these viruses. The organization of the VS is in many respects similar to the immunological synapse (IS), in particular, to the immature IS. The VS is highly enriched in the adhesion molecule lymphocyte function-associated antigen 1 (LFA-1) and its ligands intercellular adhesion molecule 1 (ICAM-1) and ICAM-3 (29); however, it does not possess the CD3-enriched central region associated with the mature IS (28, 47). While the VS is critical to the pathogenesis of HIV and HTLV-1, it remains an unanswered question whether the VS is also involved in T-cell infection by other viruses, especially those not typically considered lymphotropic.Herpes simplex virus (HSV) is a remarkably successful human pathogen that establishes lifelong latency in neurons of the dorsal root ganglia. HSV can efficiently reactivate from the latent state and transmit to new hosts despite the presence of preformed immunity. HSV is thought to achieve this feat by employing a number of sophisticated immune evasion mechanisms (33), many of which are directed at the cellular arm of the immune response. In one such potential mechanism, HSV has evolved the ability to enter and infect T cells. Although T cells do not support efficient viral replication (25), infection by HSV profoundly modulates T-cell receptor (TCR) signaling, which prevents T-cell cytotoxic function (55) and alters cytokine production profiles toward an interleukin-10-dominated immunosuppressive phenotype (54). However, it is unknown whether and to what extent HSV infection of T cells occurs during human HSV disease. Furthermore, the dominant mechanisms by which HSV might gain access to lesion-infiltrating T cells have not been elucidated.Here, we evaluated T-cell infection during human HSV infections, the mechanisms by which HSV enters T cells, the relative involvement of cell-cell spread versus cell-free virus in T-cell infection, and the role of the VS in the infection of T cells by HSV. The demonstration of infection of T cells in human HSV disease and of a dominant role for the VS in entry of HSV into T cells suggests that the VS is important in the pathogenesis of nonlymphotropic as well as lymphotropic viruses. Thus, the VS may be a unique pharmacologic target to allow improved immune control of a wide variety of viral infections.