Herpes simplex virus type 2 infection
Abstract
Epidemiological and clinical data indicate that genital ulcer disease (GUD) pathogens are associated with an increased risk of human immunodeficiency virus type 1 (HIV-1) acquisition and/or transmission. Among them, genital herpes simplex virus type 2 (HSV-2) seems to play a relevant role. Indeed, the ability of HSV-2 to induce massive infiltration at the genital level of cells which are potential targets for HIV-1 infection may represent one of the mechanisms involved in this process. Here we show that infection of human primary macrophages (MDMs) by HSV-2 results in an increase of CCR5 expression levels on cell surface and allows higher efficiency of MDMs to support entry of R5 HIV-1 strains. This finding could strengthen, at the molecular level, the evidence linking HSV-2 infection to an increased susceptibility to HIV-1 acquisition.
Findings
Herpes simplex virus (HSV), and especially HSV type 2, represents one of the most widely spread pathogen causing genital ulcer disease (GUD). Different studies have associated GUD aetiological agents in general, and HSV-2 in particular, with a higher risk to acquire and/or transmit HIV-1 infection. A number of biological and molecular factors may explain this evidence. Both the physical disruption of the epithelial/mucosal barrier and the cellular inflammatory response characterizing GUD could facilitate HIV-1 acquisition, by providing the virus with access to a large number of CD4-positive cells. Moreover, several in vitro studies have underlined molecular mechanisms by which HSV can directly influence the HIV life cycle in HSV-HIV coinfected cells. Finally, randomised controlled trials have been conducted in coinfected individuals to evaluate the effect of HSV-2 suppressive therapy on HIV-1 genital shedding and plasma HIV-1 RNA, showing, in most cases, a negative impact on HIV-1 replication. A recent study conducted by Zhu and co-workers showed a persistence of HIV receptor-positive cells in genital skin after HSV reactivation. In the genital tract, macrophages represent one of the main target of HIV-1, especially during primary infection. In this study we wanted to analyze the ability of HSV-2 to infect human macrophages and to influence HIV-1 super-infection.
Firstly, we selected the human monocyte U937 cell line (ATCC® Number CRL-1593.2) as experimental set and we infected them with HSV-2, strain G (kindly provided by Dr. Peggy Marconi, University of Ferrara, Italy). Briefly, the virus was grown and titrated by plaque assay on African green monkey kidney cells (Vero), as previously described. U937 cells (1 × 106) were infected with HSV-2 at two different multiplicity of infection (MOI of 1 and 10 plaque forming unit, PFU, per cell). Cells were left in contact with the virus for two hours at 37°C and, after three washing with phosphate buffered saline (PBS), cultured in Roswell Park Memorial Institute medium (RPMI 1640), with addition of 10% heat-inactivated foetal bovine serum (complete medium). HSV-2 replication was followed by titration of the virus released in the cellular supernatant. In contrast with fully permissive Vero cells, our data show that U937 cells do not support a significant HSV-2 replication and that, at least in the case of the MOI of 1 PFU/cell, the viral titre declines over time. It has been previously reported that monocytes display an intrinsic resistance to HSV type 1 (HSV-1) infection, depending on the cellular differentiation level along the monocytic pathway into functionally and morphologically mature non-proliferating cells, that can be achieved by 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment.